diff --git a/.clang-format b/.clang-format
index de1c8b5c77f756..41d4cd23fd97f5 100644
--- a/.clang-format
+++ b/.clang-format
@@ -149,7 +149,7 @@ Cpp11BracedListStyle: false
 
 # A list of macros that should be interpreted as foreach loops instead of as
 # function calls.
-ForEachMacros: ['for_each_string_list_item']
+ForEachMacros: ['for_each_string_list_item', 'for_each_wanted_builtin', 'for_each_builtin', 'for_each_ut']
 
 # The maximum number of consecutive empty lines to keep.
 MaxEmptyLinesToKeep: 1
diff --git a/BRANCHES.md b/BRANCHES.md
new file mode 100644
index 00000000000000..cecee7cf7ba6ab
--- /dev/null
+++ b/BRANCHES.md
@@ -0,0 +1,53 @@
+Branches used in this repo
+==========================
+
+The document explains the branching structure that we are using in the VFSForGit repository as well as the forking strategy that we have adopted for contributing.
+
+Repo Branches
+-------------
+
+1. master
+
+    This will track the Git for Windows repository master branch
+
+2. vfs
+
+    Would like to use this branch as an ever-green branch that continually rebases the VFSForGit changes onto a windows ever-green branch that is on the core/master, so that we can detect when the patches for VFSForGit have issues or if we have a new version patches sent upstream git we can regenerate this branch.
+
+3. vs/master
+
+    This tracks with the Git for Windows repository vs/master branch and are the generated files for using a Visual Studio solution.
+
+4. vfs-#
+
+    These branches are used to track the specific version that match Git for Windows with the VFSForGit specific patches on top.  When a new version of Git for Windows is released, the VFSForGit patches will be rebased on that windows version and a new gvfs-# branch created to create pull requests against.
+
+    #### Examples
+
+    ```
+    vfs-2.20.0
+    vfs-2.20.1
+    ```
+
+    The versions of git for VFSForGit are based on the Git for Windows versions.  v2.20.0.vfs.1 will correspond with the v2.20.0.windows.1 with the VFSForGit specific patches applied to the windows version.
+
+Tags
+----
+
+We are using annotated tags to build the version number for git.  The build will look back through the commit history to find the first tag matching `v[0-9]*vfs*` and build the git version number using that tag.
+
+Forking
+-------
+
+A personal fork of this repository and a branch in that repository should be used for development.
+
+These branches should be based on the latest vfs-# branch.  If there are work in progress pull requests that you have based on a previous version branch when a new version branch is created, you will need to move your patches to the new branch to get them in that latest version.
+
+#### Example
+
+```
+git clone <personal fork repo URL>
+git remote add ms https://github.com/Microsoft/git.git
+git checkout -b my-changes ms/vfs-2.20.0 --no-track
+git push -fu origin HEAD
+```
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 7b3cdd1f8d95cc..24b433169b5b7c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -426,6 +426,8 @@ include::config/submodule.txt[]
 
 include::config/tag.txt[]
 
+include::config/trace2.txt[]
+
 include::config/transfer.txt[]
 
 include::config/uploadarchive.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 71dce85e76926c..ef30ccd3648afb 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -68,6 +68,14 @@ core.fsmonitor::
 	avoiding unnecessary processing of files that have not changed.
 	See the "fsmonitor-watchman" section of linkgit:githooks[5].
 
+core.virtualFilesystem::
+	If set, the value of this variable is used as a command which
+	will identify all files and directories that are present in
+	the working directory.  Git will only track and update files
+	listed in the virtual file system.  Using the virtual file system
+	will supersede the sparse-checkout settings which will be ignored.
+	See the "virtual file system" section of linkgit:githooks[5].
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
@@ -603,6 +611,48 @@ core.multiPackIndex::
 	single index. See link:technical/multi-pack-index.html[the
 	multi-pack-index design document].
 
+core.gvfs::
+	Enable the features needed for GVFS.  This value can be set to true
+	to indicate all features should be turned on or the bit values listed
+	below can be used to turn on specific features.
++
+--
+	GVFS_SKIP_SHA_ON_INDEX::
+		Bit value 1
+		Disables the calculation of the sha when writing the index
+	GVFS_MISSING_OK::
+		Bit value 4
+		Normally git write-tree ensures that the objects referenced by the
+		directory exist in the object database. This option disables this check.
+	GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT::
+		Bit value 8
+		When marking entries to remove from the index and the working
+		directory this option will take into account what the
+		skip-worktree bit was set to so that if the entry has the
+		skip-worktree bit set it will not be removed from the working
+		directory.  This will allow virtualized working directories to
+		detect the change to HEAD and use the new commit tree to show
+		the files that are in the working directory.
+	GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK::
+		Bit value 16
+		While performing a fetch with a virtual file system we know
+		that there will be missing objects and we don't want to download
+		them just because of the reachability of the commits.  We also
+		don't want to download a pack file with commits, trees, and blobs
+		since these will be downloaded on demand.  This flag will skip the
+		checks on the reachability of objects during a fetch as well as
+		the upload pack so that extraneous objects don't get downloaded.
+	GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS::
+		Bit value 64
+		With a virtual file system we only know the file size before any
+		CRLF or smudge/clean filters processing is done on the client.
+		To prevent file corruption due to truncation or expansion with
+		garbage at the end, these filters must not run when the file
+		is first accessed and brought down to the client. Git.exe can't
+		currently tell the first access vs subsequent accesses so this
+		flag just blocks them from occurring at all.
+--
+
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See section "Sparse checkout" in
 	linkgit:git-read-tree[1] for more information.
diff --git a/Documentation/config/status.txt b/Documentation/config/status.txt
index ed72fa7daece09..1f20eb5551e4c0 100644
--- a/Documentation/config/status.txt
+++ b/Documentation/config/status.txt
@@ -12,6 +12,11 @@ status.branch::
 	Set to true to enable --branch by default in linkgit:git-status[1].
 	The option --no-branch takes precedence over this variable.
 
+status.aheadBehind::
+	EXPERIMENTAL, Set to true to enable --ahead-behind and false to
+	enable --no-ahead-behind by default in linkgit:git-status[1] for
+	non-porcelain status formats.  Defaults to true.
+
 status.displayCommentPrefix::
 	If set to true, linkgit:git-status[1] will insert a comment
 	prefix before each output line (starting with
@@ -70,3 +75,25 @@ status.submoduleSummary::
 	the --ignore-submodules=dirty command-line option or the 'git
 	submodule summary' command, which shows a similar output but does
 	not honor these settings.
+
+status.deserializePath::
+	EXPERIMENTAL, Pathname to a file containing cached status results
+	generated by `--serialize`.  This will be overridden by
+	`--deserialize=<path>` on the command line.  If the cache file is
+	invalid or stale, git will fall-back and compute status normally.
+
+status.deserializeWait::
+	EXPERIMENTAL, Specifies what `git status --deserialize` should do
+	if the serialization cache file is stale and whether it should
+	fall-back and compute status normally.  This will be overridden by
+	`--deserialize-wait=<value>` on the command line.
++
+--
+* `fail` - cause git to exit with an error when the status cache file
+is stale; this is intended for testing and debugging.
+* `block` - cause git to spin and periodically retry the cache file
+every 100 ms; this is intended to help coordinate with another git
+instance concurrently computing the cache file.
+* `no` - to immediately fall-back if cache file is stale.  This is the default.
+* `<timeout>` - time (in tenths of a second) to spin and retry.
+--
diff --git a/Documentation/config/trace2.txt b/Documentation/config/trace2.txt
new file mode 100644
index 00000000000000..a5f409c1c13c55
--- /dev/null
+++ b/Documentation/config/trace2.txt
@@ -0,0 +1,56 @@
+Trace2 config settings are only read from the system and global
+config files; repository local and worktree config files and `-c`
+command line arguments are not respected.
+
+trace2.normalTarget::
+	This variable controls the normal target destination.
+	It may be overridden by the `GIT_TR2` environment variable.
+	The following table shows possible values.
+
+trace2.perfTarget::
+	This variable controls the performance target destination.
+	It may be overridden by the `GIT_TR2_PERF` environment variable.
+	The following table shows possible values.
+
+trace2.eventTarget::
+	This variable controls the event target destination.
+	It may be overridden by the `GIT_TR2_EVENT` environment variable.
+	The following table shows possible values.
++
+include::../trace2-target-values.txt[]
+
+trace2.normalBrief::
+	Boolean.  When true `time`, `filename`, and `line` fields are
+	omitted from normal output.  May be overridden by the
+	`GIT_TR2_BRIEF` environment variable.  Defaults to false.
+
+trace2.perfBrief::
+	Boolean.  When true `time`, `filename`, and `line` fields are
+	omitted from PERF output.  May be overridden by the
+	`GIT_TR2_PERF_BRIEF` environment variable.  Defaults to false.
+
+trace2.eventBrief::
+	Boolean.  When true `time`, `filename`, and `line` fields are
+	omitted from event output.  May be overridden by the
+	`GIT_TR2_EVENT_BRIEF` environment variable.  Defaults to false.
+
+trace2.eventNesting::
+	Integer.  Specifies desired depth of nested regions in the
+	event output.  Regions deeper than this value will be
+	omitted.  May be overridden by the `GIT_TR2_EVENT_NESTING`
+	environment variable.  Defaults to 2.
+
+trace2.configParams::
+	A comma-separated list of patterns of "important" config
+	settings that should be recorded in the trace2 output.
+	For example, `core.*,remote.*.url` would cause the trace2
+	output to contain events listing each configured remote.
+	May be overridden by the `GIT_TR2_CONFIG_PARAMS` environment
+	variable.  Unset by default.
+
+trace2.destinationDebug::
+	Boolean.  When true Git will print error messages when a
+	trace target destination cannot be opened for writing.
+	By default, these errors are suppressed and tracing is
+	silently disabled.  May be overridden by the
+	`GIT_TR2_DST_DEBUG` environment variable.
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index fa0a3151b3f7e9..3680082ae7ebc6 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -220,6 +220,19 @@ endif::git-pull[]
 	When multiple `--server-option=<option>` are given, they are all
 	sent to the other side in the order listed on the command line.
 
+--show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. This can be disabled through fetch.showForcedUpdates, but
+	the --show-forced-updates option guarantees this check occurs.
+	See linkgit:git-config[1].
+
+--no-show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. Pass --no-show-forced-updates or set fetch.showForcedUpdates
+	to false to skip this check for performance reasons. If used during
+	'git-pull' the --ff-only option will still check for forced updates
+	before attempting a fast-forward update. See linkgit:git-config[1].
+
 -4::
 --ipv4::
 	Use IPv4 addresses only, ignoring IPv6 addresses.
diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index f7778a2c85c1aa..cc63531cc02b77 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -9,7 +9,7 @@ git-multi-pack-index - Write and verify multi-pack-indexes
 SYNOPSIS
 --------
 [verse]
-'git multi-pack-index' [--object-dir=<dir>] <verb>
+'git multi-pack-index' [--object-dir=<dir>] <subcommand>
 
 DESCRIPTION
 -----------
@@ -23,13 +23,29 @@ OPTIONS
 	`<dir>/packs/multi-pack-index` for the current MIDX file, and
 	`<dir>/packs` for the pack-files to index.
 
+The following subcommands are available:
+
 write::
-	When given as the verb, write a new MIDX file to
-	`<dir>/packs/multi-pack-index`.
+	Write a new MIDX file.
 
 verify::
-	When given as the verb, verify the contents of the MIDX file
-	at `<dir>/packs/multi-pack-index`.
+	Verify the contents of the MIDX file.
+
+expire::
+	Delete the pack-files that are tracked 	by the MIDX file, but
+	have no objects referenced by the MIDX. Rewrite the MIDX file
+	afterward to remove all references to these pack-files.
+
+repack::
+	Collect a batch of pack-files whose size are all at most the
+	size given by --batch-size, but whose sizes sum to larger
+	than --batch-size. The batch is selected by greedily adding
+	small pack-files starting with the oldest pack-files that fit
+	the size. Create a new pack-file containing the objects the
+	multi-pack-index indexes into those pack-files, and rewrite
+	the multi-pack-index to contain that pack-file. A later run
+	of 'git multi-pack-index expire' will delete the pack-files
+	that were part of this batch.
 
 
 EXAMPLES
diff --git a/Documentation/git-status.txt b/Documentation/git-status.txt
index e5756a6b668373..b0ffe5a9e8ecda 100644
--- a/Documentation/git-status.txt
+++ b/Documentation/git-status.txt
@@ -152,6 +152,21 @@ ignored, then the directory is not shown, but all contents are shown.
 	update it afterwards if any changes were detected. Defaults to
 	`--lock-index`.
 
+--serialize[=<path>]::
+	(EXPERIMENTAL) Serialize raw status results to a file or stdout
+	in a format suitable for use by `--deserialize`.  If a path is
+	given, serialize data will be written to that path *and* normal
+	status output will be written to stdout.  If path is omitted,
+	only binary serialization data will be written to stdout.
+
+--deserialize[=<path>]::
+	(EXPERIMENTAL) Deserialize raw status results from a file or
+	stdin rather than scanning the worktree.  If `<path>` is omitted
+	and `status.deserializePath` is unset, input is read from stdin.
+--no-deserialize::
+	(EXPERIMENTAL) Disable implicit deserialization of status results
+	from the value of `status.deserializePath`.
+
 <pathspec>...::
 	See the 'pathspec' entry in linkgit:gitglossary[7].
 
@@ -397,6 +412,26 @@ quoted as explained for the configuration variable `core.quotePath`
 (see linkgit:git-config[1]).
 
 
+SERIALIZATION and DESERIALIZATION (EXPERIMENTAL)
+------------------------------------------------
+
+The `--serialize` option allows git to cache the result of a
+possibly time-consuming status scan to a binary file.  A local
+service/daemon watching file system events could use this to
+periodically pre-compute a fresh status result.
+
+Interactive users could then use `--deserialize` to simply
+(and immediately) print the last-known-good result without
+waiting for the status scan.
+
+The binary serialization file format includes some worktree state
+information allowing `--deserialize` to reject the cached data
+and force a normal status scan if, for example, the commit, branch,
+or status modes/options change.  The format cannot, however, indicate
+when the cached data is otherwise stale -- that coordination belongs
+to the task driving the serializations.
+
+
 CONFIGURATION
 -------------
 
diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 959044347e5ee0..1a90bc01d704c9 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -492,6 +492,44 @@ This hook is invoked by `git-p4 submit`. It takes no parameters and nothing
 from standard input. Exiting with non-zero status from this script prevent
 `git-p4 submit` from launching. Run `git-p4 submit --help` for details.
 
+virtualFilesystem
+~~~~~~~~~~~~~~~~~~
+
+"Virtual File System" allows populating the working directory sparsely.
+The projection data is typically automatically generated by an external
+process.  Git will limit what files it checks for changes as well as which
+directories are checked for untracked files based on the path names given.
+Git will also only update those files listed in the projection.
+
+The hook is invoked when the configuration option core.virtualFilesystem
+is set.  It takes one argument, a version (currently 1).
+
+The hook should output to stdout the list of all files in the working
+directory that git should track.  The paths are relative to the root
+of the working directory and are separated by a single NUL.  Full paths
+('dir1/a.txt') as well as directories are supported (ie 'dir1/').
+
+The exit status determines whether git will use the data from the
+hook.  On error, git will abort the command with an error message.
+
+post-indexchanged
+~~~~~~~~~~~~~~~~~
+
+This hook is invoked when the index is written in read-cache.c
+do_write_locked_index.
+
+The first parameter passed to the hook is the indicator for the
+working directory being updated.  "1" meaning working directory
+was updated or "0" when the working directory was not updated.
+
+The second parameter passed to the hook is the indicator for whether
+or not the index was updated and the skip-worktree bit could have
+changed.  "1" meaning skip-worktree bits could have been updated
+and "0" meaning they were not.
+
+Only one parameter should be set to "1" when the hook runs.  The hook
+running passing "1", "1" should not be possible.
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
new file mode 100644
index 00000000000000..8b6a5e6d4b9856
--- /dev/null
+++ b/Documentation/technical/api-trace2.txt
@@ -0,0 +1,1373 @@
+= Trace2 API
+
+The Trace2 API can be used to print debug, performance, and telemetry
+information to stderr or a file.  The Trace2 feature is inactive unless
+explicitly enabled by enabling one or more Trace2 Targets.
+
+The Trace2 API is intended to replace the existing (Trace1)
+printf-style tracing provided by the existing `GIT_TRACE` and
+`GIT_TRACE_PERFORMANCE` facilities.  During initial implementation,
+Trace2 and Trace1 may operate in parallel.
+
+The Trace2 API defines a set of high-level messages with known fields,
+such as (`start`: `argv`) and (`exit`: {`exit-code`, `elapsed-time`}).
+
+Trace2 instrumentation throughout the Git code base sends Trace2
+messages to the enabled Trace2 Targets.  Targets transform these
+messages content into purpose-specific formats and write events to
+their data streams.  In this manner, the Trace2 API can drive
+many different types of analysis.
+
+Targets are defined using a VTable allowing easy extension to other
+formats in the future.  This might be used to define a binary format,
+for example.
+
+Trace2 is controlled using `trace2.*` config values in the system and
+global config files and `GIT_TR2*` environment variables.  Trace2 does
+not read from repo local or worktree config files or respect `-c`
+command line config settings.
+
+== Trace2 Targets
+
+Trace2 defines the following set of Trace2 Targets.
+Format details are given in a later section.
+
+=== The Normal Format Target
+
+The normal format target is a tradition printf format and similar
+to GIT_TRACE format.  This format is enabled with the `GIT_TR`
+environment variable or the `trace2.normalTarget` system or global
+config setting.
+
+For example
+
+------------
+$ export GIT_TR2=~/log.normal
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+or
+
+------------
+$ git config --global trace2.normalTarget ~/log.normal
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+yields
+
+------------
+$ cat ~/log.normal
+12:28:42.620009 common-main.c:38                  version 2.20.1.155.g426c96fcdb
+12:28:42.620989 common-main.c:39                  start git version
+12:28:42.621101 git.c:432                         cmd_name version (version)
+12:28:42.621215 git.c:662                         exit elapsed:0.001227 code:0
+12:28:42.621250 trace2/tr2_tgt_normal.c:124       atexit elapsed:0.001265 code:0
+------------
+
+=== The Performance Format Target
+
+The performance format target (PERF) is a column-based format to
+replace GIT_TRACE_PERFORMANCE and is suitable for development and
+testing, possibly to complement tools like gprof.  This format is
+enabled with the `GIT_TR2_PERF` environment variable or the
+`trace2.perfTarget` system or global config setting.
+
+For example
+
+------------
+$ export GIT_TR2_PERF=~/log.perf
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+or
+
+------------
+$ git config --global trace2.perfTarget ~/log.perf
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+yields
+
+------------
+$ cat ~/log.perf
+12:28:42.620675 common-main.c:38                  | d0 | main                     | version      |     |           |           |            | 2.20.1.155.g426c96fcdb
+12:28:42.621001 common-main.c:39                  | d0 | main                     | start        |     |  0.001173 |           |            | git version
+12:28:42.621111 git.c:432                         | d0 | main                     | cmd_name     |     |           |           |            | version (version)
+12:28:42.621225 git.c:662                         | d0 | main                     | exit         |     |  0.001227 |           |            | code:0
+12:28:42.621259 trace2/tr2_tgt_perf.c:211         | d0 | main                     | atexit       |     |  0.001265 |           |            | code:0
+------------
+
+=== The Event Format Target
+
+The event format target is a JSON-based format of event data suitable
+for telemetry analysis.  This format is enabled with the `GIT_TR2_EVENT`
+environment variable or the `trace2.eventTarget` system or global config
+setting.
+
+For example
+
+------------
+$ export GIT_TR2_EVENT=~/log.event
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+or
+
+------------
+$ git config --global trace2.eventTarget ~/log.event
+$ git version
+git version 2.20.1.155.g426c96fcdb
+------------
+
+yields
+
+------------
+$ cat ~/log.event
+{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"1","exe":"2.20.1.155.g426c96fcdb"}
+{"event":"start","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621027Z","file":"common-main.c","line":39,"t_abs":0.001173,"argv":["git","version"]}
+{"event":"cmd_name","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621122Z","file":"git.c","line":432,"name":"version","hierarchy":"version"}
+{"event":"exit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621236Z","file":"git.c","line":662,"t_abs":0.001227,"code":0}
+{"event":"atexit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621268Z","file":"trace2/tr2_tgt_event.c","line":163,"t_abs":0.001265,"code":0}
+------------
+
+=== Enabling a Target
+
+To enable a target, set the corresponding environment variable or
+system or global config value to one of the following:
+
+include::../trace2-target-values.txt[]
+
+== Trace2 API
+
+All public Trace2 functions and macros are defined in `trace2.h` and
+`trace2.c`.  All public symbols are prefixed with `trace2_`.
+
+There are no public Trace2 data structures.
+
+The Trace2 code also defines a set of private functions and data types
+in the `trace2/` directory.  These symbols are prefixed with `tr2_`
+and should only be used by functions in `trace2.c`.
+
+== Conventions for Public Functions and Macros
+
+The functions defined by the Trace2 API are declared and documented
+in `trace2.h`.  It defines the API functions and wrapper macros for
+Trace2.
+
+Some functions have a `_fl()` suffix to indicate that they take `file`
+and `line-number` arguments.
+
+Some functions have a `_va_fl()` suffix to indicate that they also
+take a `va_list` argument.
+
+Some functions have a `_printf_fl()` suffix to indicate that they also
+take a varargs argument.
+
+There are CPP wrapper macros and ifdefs to hide most of these details.
+See `trace2.h` for more details.  The following discussion will only
+describe the simplified forms.
+
+== Public API
+
+All Trace2 API functions send a messsage to all of the active
+Trace2 Targets.  This section describes the set of available
+messages.
+
+It helps to divide these functions into groups for discussion
+purposes.
+
+=== Basic Command Messages
+
+These are concerned with the lifetime of the overall git process.
+
+`void trace2_initialize_clock()`::
+
+	Initialize the Trace2 start clock and nothing else.  This should
+	be called at the very top of main() to capture the process start
+	time and reduce startup order dependencies.
+
+`void trace2_initialize()`::
+
+	Determines if any Trace2 Targets should be enabled and
+	initializes the Trace2 facility.  This includes setting up the
+	Trace2 thread local storage (TLS).
++
+This function emits a "version" message containing the version of git
+and the Trace2 protocol.
++
+This function should be called from `main()` as early as possible in
+the life of the process after essential process initialization.
+
+`int trace2_is_enabled()`::
+
+	Returns 1 if Trace2 is enabled (at least one target is
+	active).
+
+`void trace2_cmd_start(int argc, const char **argv)`::
+
+	Emits a "start" message containing the process command line
+	arguments.
+
+`int trace2_cmd_exit(int exit_code)`::
+
+	Emits an "exit" message containing the process exit-code and
+	elapsed time.
++
+Returns the exit-code.
+
+`void trace2_cmd_error(const char *fmt, va_list ap)`::
+
+	Emits an "error" message containing a formatted error message.
+
+`void trace2_cmd_path(const char *pathname)`::
+
+	Emits a "cmd_path" message with the full pathname of the
+	current process.
+
+=== Command Detail Messages
+
+These are concerned with describing the specific Git command
+after the command line, config, and environment are inspected.
+
+`void trace2_cmd_name(const char *name)`::
+
+	Emits a "cmd_name" message with the canonical name of the
+	command, for example "status" or "checkout".
+
+`void trace2_cmd_mode(const char *mode)`::
+
+	Emits a "cmd_mode" message with a qualifier name to further
+	describe the current git command.
++
+This message is intended to be used with git commands having multiple
+major modes.  For example, a "checkout" command can checkout a new
+branch or it can checkout a single file, so the checkout code could
+emit a cmd_mode message of "branch" or "file".
+
+`void trace2_cmd_alias(const char *alias, const char **argv_expansion)`::
+
+	Emits an "alias" message containing the alias used and the
+	argument expansion.
+
+`void trace2_def_param(const char *parameter, const char *value)`::
+
+	Emits a "def_param" message containing a key/value pair.
++
+This message is intended to report some global aspect of the current
+command, such as a configuration setting or command line switch that
+significantly affects program performance or behavior, such as
+`core.abbrev`, `status.showUntrackedFiles`, or `--no-ahead-behind`.
+
+`void trace2_cmd_list_config()`::
+
+	Emits a "def_param" messages for "important" configuration
+	settings.
++
+The environment variable `GIT_TR2_CONFIG_PARAMS` or the `trace2.configParams`
+config value can be set to a
+list of patterns of important configuration settings, for example:
+`core.*,remote.*.url`.  This function will iterate over all config
+settings and emit a "def_param" message for each match.
+
+`void trace2_cmd_set_config(const char *key, const char *value)`::
+
+	Emits a "def_param" message for a new or updated key/value
+	pair IF `key` is considered important.
++
+This is used to hook into `git_config_set()` and catch any
+configuration changes and update a value previously reported by
+`trace2_cmd_list_config()`.
+
+`void trace2_def_repo(struct repository *repo)`::
+
+	Registers a repository with the Trace2 layer.  Assigns a
+	unique "repo-id" to `repo->trace2_repo_id`.
++
+Emits a "worktree" messages containing the repo-id and the worktree
+pathname.
++
+Region and data messages (described later) may refer to this repo-id.
++
+The main/top-level repository will have repo-id value 1 (aka "r1").
++
+The repo-id field is in anticipation of future in-proc submodule
+repositories.
+
+=== Child Process Messages
+
+These are concerned with the various spawned child processes,
+including shell scripts, git commands, editors, pagers, and hooks.
+
+`void trace2_child_start(struct child_process *cmd)`::
+
+	Emits a "child_start" message containing the "child-id",
+	"child-argv", and "child-classification".
++
+Before calling this, set `cmd->trace2_child_class` to a name
+describing the type of child process, for example "editor".
++
+This function assigns a unique "child-id" to `cmd->trace2_child_id`.
+This field is used later during the "child_exit" message to associate
+it with the "child_start" message.
++
+This function should be called before spawning the child process.
+
+`void trace2_child_exit(struct child_proess *cmd, int child_exit_code)`::
+
+	Emits a "child_exit" message containing the "child-id",
+	the child's elapsed time and exit-code.
++
+The reported elapsed time includes the process creation overhead and
+time spend waiting for it to exit, so it may be slightly longer than
+the time reported by the child itself.
++
+This function should be called after reaping the child process.
+
+`int trace2_exec(const char *exe, const char **argv)`::
+
+	Emits a "exec" message containing the "exec-id" and the
+	argv of the new process.
++
+This function should be called before calling one of the `exec()`
+variants, such as `execvp()`.
++
+This function returns a unique "exec-id".  This value is used later
+if the exec() fails and a "exec-result" message is necessary.
+
+`void trace2_exec_result(int exec_id, int error_code)`::
+
+	Emits a "exec_result" message containing the "exec-id"
+	and the error code.
++
+On Unix-based systems, `exec()` does not return if successful.
+This message is used to indicate that the `exec()` failed and
+that the current program is continuing.
+
+=== Git Thread Messages
+
+These messages are concerned with Git thread usage.
+
+`void trace2_thread_start(const char *thread_name)`::
+
+	Emits a "thread_start" message.
++
+The `thread_name` field should be a descriptive name, such as the
+unique name of the thread-proc.  A unique "thread-id" will be added
+to the name to uniquely identify thread instances.
++
+Region and data messages (described later) may refer to this thread
+name.
++
+This function must be called by the thread-proc of the new thread
+(so that TLS data is properly initialized) and not by the caller
+of `pthread_create()`.
+
+`void trace2_thread_exit()`::
+
+	Emits a "thread_exit" message containing the thread name
+	and the thread elapsed time.
++
+This function must be called by the thread-proc before it returns
+(so that the coorect TLS data is used and cleaned up.  It should
+not be called by the caller of `pthread_join()`.
+
+=== Region and Data Messages
+
+These are concerned with recording performance data
+over regions or spans of code.
+
+`void trace2_region_enter(const char *category, const char *label, const struct repository *repo)`::
+
+`void trace2_region_enter_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`::
+
+`void trace2_region_enter_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`::
+
+	Emits a thread-relative "region_enter" message with optional
+	printf string.
++
+This function pushes a new region nesting stack level on the current
+thread and starts a clock for the new stack frame.
++
+The `category` field is an arbitrary category name used to classify
+regions by feature area, such as "status" or "index".  At this time
+it is only just printed along with the rest of the message.  It may
+be used in the future to filter messages.
++
+The `label` field is an arbitrary label used to describe the activity
+being started, such as "read_recursive" or "do_read_index".
++
+The `repo` field, if set, will be used to get the "repo-id", so that
+recursive oerations can be attributed to the correct repository.
+
+`void trace2_region_leave(const char *category, const char *label, const struct repository *repo)`::
+
+`void trace2_region_leave_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`::
+
+`void trace2_region_leave_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`::
+
+	Emits a thread-relative "region_leave" message with optional
+	printf string.
++
+This function pops the region nesting stack on the current thread
+and reports the elapsed time of the stack frame.
++
+The `category`, `label`, and `repo` fields are the same as above.
+The `category` and `label` do not need to match the correpsonding
+"region_enter" message, but it makes the data stream easier to
+understand.
+
+`void trace2_data_string(const char *category, const struct repository *repo, const char *key, const char * value)`::
+
+`void trace2_data_intmax(const char *category, const struct repository *repo, const char *key, intmax value)`::
+
+`void trace2_data_json(const char *category, const struct repository *repo, const char *key, const struct json_writer *jw)`::
+
+	Emits a region- and thread-relative "data" or "data_json" message.
++
+This is a key/value pair message containing information about the
+current thread, region stack, and repository.  This could be used
+to print the number of files in a directory during a multi-threaded
+recursive tree walk.
+
+`void trace2_printf(const char *fmt, ...)`::
+
+`void trace2_printf_va(const char *fmt, va_list ap)`::
+
+	Emits a region- and thread-relative "printf" message.
+
+== Trace2 Target Formats
+
+=== NORMAL Format
+
+Events are written as lines of the form:
+
+------------
+[<time> SP <filename>:<line> SP+] <event-name> [[SP] <event-message>] LF
+------------
+
+`<event-name>`::
+
+	is the event name.
+
+`<event-message>`::
+	is a free-form printf message intended for human consumption.
++
+Note that this may contain embedded LF or CRLF characters that are
+not escaped, so the event may spill across multiple lines.
+
+If `GIT_TR2_BRIEF` or `trace2.normalBrief` is true, the `time`, `filename`,
+and `line` fields are omitted.
+
+This target is intended to be more of a summary (like GIT_TRACE) and
+less detailed than the other targets.  It ignores thread, region, and
+data messages, for example.
+
+=== PERF Format
+
+Events are written as lines of the form:
+
+------------
+[<time> SP <filename>:<line> SP+
+    BAR SP] d<depth> SP
+    BAR SP <thread-name> SP+
+    BAR SP <event-name> SP+
+    BAR SP [r<repo-id>] SP+
+    BAR SP [<t_abs>] SP+
+    BAR SP [<t_rel>] SP+
+    BAR SP [<category>] SP+
+    BAR SP DOTS* <perf-event-message>
+    LF
+------------
+
+`<depth>`::
+	is the git process depth.  This is the number of parent
+	git processes.  A top-level git command has depth value "d0".
+	A child of it has depth value "d1".  A second level child
+	has depth value "d2" and so on.
+
+`<thread-name>`::
+	is a unique name for the thread.  The primary thread
+	is called "main".  Other thread names are of the form "th%d:%s"
+	and include a unique number and the name of the thread-proc.
+
+`<event-name>`::
+	is the event name.
+
+`<repo-id>`::
+	when present, is a number indicating the repository
+	in use.  A `def_repo` event is emitted when a repository is
+	opened.  This defines the repo-id and associated worktree.
+	Subsequent repo-specific events will reference this repo-id.
++
+Currently, this is always "r1" for the main repository.
+This field is in anticipation of in-proc submodules in the future.
+
+`<t_abs>`::
+	when present, is the absolute time in seconds since the
+	program started.
+
+`<t_rel>`::
+	when present, is time in seconds relative to the start of
+	the current region.  For a thread-exit event, it is the elapsed
+	time of the thread.
+
+`<category>`::
+	is present on region and data events and is used to
+	indicate a broad category, such as "index" or "status".
+
+`<perf-event-message>`::
+	is a free-form printf message intended for human consumption.
+
+------------
+15:33:33.532712 wt-status.c:2310                  | d0 | main                     | region_enter | r1  |  0.126064 |           | status     | label:print
+15:33:33.532712 wt-status.c:2331                  | d0 | main                     | region_leave | r1  |  0.127568 |  0.001504 | status     | label:print
+------------
+
+If `GIT_TR2_PERF_BRIEF` or `trace2.perfBrief` is true, the `time`, `file`,
+and `line` fields are omitted.
+
+------------
+d0 | main                     | region_leave | r1  |  0.011717 |  0.009122 | index      | label:preload
+------------
+
+The PERF target is intended for interactive performance analysis
+during development and is quite noisy.
+
+=== EVENT Format
+
+Each event is a JSON-object containing multiple key/value pairs
+written as a single line and followed by a LF.
+
+------------
+'{' <key> ':' <value> [',' <key> ':' <value>]* '}' LF
+------------
+
+Some key/value pairs are common to all events and some are
+event-specific.
+
+==== Common Key/Value Pairs
+
+The following key/value pairs are common to all events:
+
+------------
+{
+	"event":"version",
+	"sid":"20190408T191827.272759Z-H9b68c35f-P00003510",
+	"thread":"main",
+	"time":"2019-04-08T19:18:27.282761Z",
+	"file":"common-main.c",
+	"line":42,
+	...
+}
+------------
+
+`"event":<event>`::
+	is the event name.
+
+`"sid":<sid>`::
+	is the session-id.  This is a unique string to identify the
+	process instance to allow all events emitted by a process to
+	be identified.  A session-id is used instead of a PID because
+	PIDs are recycled by the OS.  For child git processes, the
+	session-id is prepended with the session-id of the parent git
+	process to allow parent-child relationships to be identified
+	during post-processing.
+
+`"thread":<thread>`::
+	is the thread name.
+
+`"time":<time>`::
+	is the UTC time of the event.
+
+`"file":<filename>`::
+	is source file generating the event.
+
+`"line":<line-number>`::
+	is the integer source line number generating the event.
+
+`"repo":<repo-id>`::
+	when present, is the integer repo-id as described previously.
+
+If `GIT_TR2_EVENT_BRIEF` or `trace2.eventBrief` is true, the `file`
+and `line` fields are omitted from all events and the `time` field is
+only present on the "start" and "atexit" events.
+
+==== Event-Specific Key/Value Pairs
+
+`"version"`::
+	This event gives the version of the executable and the EVENT format.
++
+------------
+{
+	"event":"version",
+	...
+	"evt":"1",		       # EVENT format version
+	"exe":"2.20.1.155.g426c96fcdb" # git version
+}
+------------
+
+`"start"`::
+	This event contains the complete argv received by main().
++
+------------
+{
+	"event":"start",
+	...
+	"t_abs":0.001227, # elapsed time in seconds
+	"argv":["git","version"]
+}
+------------
+
+`"exit"`::
+	This event is emitted when git calls `exit()`.
++
+------------
+{
+	"event":"exit",
+	...
+	"t_abs":0.001227, # elapsed time in seconds
+	"code":0	  # exit code
+}
+------------
+
+`"atexit"`::
+	This event is emitted by the Trace2 `atexit` routine during
+	final shutdown.  It should be the last event emitted by the
+	process.
++
+(The elapsed time reported here is greater than the time reported in
+the "exit" event because it runs after all other atexit tasks have
+completed.)
++
+------------
+{
+	"event":"atexit",
+	...
+	"t_abs":0.001227, # elapsed time in seconds
+	"code":0          # exit code
+}
+------------
+
+`"signal"`::
+	This event is emitted when the program is terminated by a user
+	signal.  Depending on the platform, the signal event may
+	prevent the "atexit" event from being generated.
++
+------------
+{
+	"event":"signal",
+	...
+	"t_abs":0.001227,  # elapsed time in seconds
+	"signal":13        # SIGTERM, SIGINT, etc.
+}
+------------
+
+`"error"`::
+	This event is emitted when one of the `error()`, `die()`,
+	or `usage()` functions are called.
++
+------------
+{
+	"event":"error",
+	...
+	"msg":"invalid option: --cahced", # formatted error message
+	"fmt":"invalid option: %s"	  # error format string
+}
+------------
++
+The error event may be emitted more than once.  The format string
+allows post-processors to group errors by type without worrying
+about specific error arguments.
+
+`"cmd_path"`::
+	This event contains the discovered full path of the git
+	executable (on platforms that are configured to resolve it).
++
+------------
+{
+	"event":"cmd_path",
+	...
+	"path":"C:/work/gfw/git.exe"
+}
+------------
+
+`"cmd_name"`::
+	This event contains the command name for this git process
+	and the hierarchy of commands from parent git processes.
++
+------------
+{
+	"event":"cmd_name",
+	...
+	"name":"pack-objects",
+	"hierarchy":"push/pack-objects"
+}
+------------
++
+Normally, the "name" field contains the canonical name of the
+command.  When a canonical name is not available, one of
+these special values are used:
++
+------------
+"_query_"            # "git --html-path"
+"_run_dashed_"       # when "git foo" tries to run "git-foo"
+"_run_shell_alias_"  # alias expansion to a shell command
+"_run_git_alias_"    # alias expansion to a git command
+"_usage_"            # usage error
+------------
+
+`"cmd_mode"`::
+	This event, when present, describes the command variant This
+	event may be emitted more than once.
++
+------------
+{
+	"event":"cmd_mode",
+	...
+	"name":"branch"
+}
+------------
++
+The "name" field is an arbitrary string to describe the command mode.
+For example, checkout can checkout a branch or an individual file.
+And these variations typically have different performance
+characteristics that are not comparable.
+
+`"alias"`::
+	This event is present when an alias is expanded.
++
+------------
+{
+	"event":"alias",
+	...
+	"alias":"l",		 # registered alias
+	"argv":["log","--graph"] # alias expansion
+}
+------------
+
+`"child_start"`::
+	This event describes a child process that is about to be
+	spawned.
++
+------------
+{
+	"event":"child_start",
+	...
+	"child_id":2,
+	"child_class":"?",
+	"use_shell":false,
+	"argv":["git","rev-list","--objects","--stdin","--not","--all","--quiet"]
+
+	"hook_name":"<hook_name>"  # present when child_class is "hook"
+	"cd":"<path>"		   # present when cd is required
+}
+------------
++
+The "child_id" field can be used to match this child_start with the
+corresponding child_exit event.
++
+The "child_class" field is a rough classification, such as "editor",
+"pager", "transport/*", and "hook".  Unclassified children are classified
+with "?".
+
+`"child_exit"`::
+	This event is generated after the current process has returned
+	from the waitpid() and collected the exit information from the
+	child.
++
+------------
+{
+	"event":"child_exit",
+	...
+	"child_id":2,
+	"pid":14708,	 # child PID
+	"code":0,	 # child exit-code
+	"t_rel":0.110605 # observed run-time of child process
+}
+------------
++
+Note that the session-id of the child process is not available to
+the current/spawning process, so the child's PID is reported here as
+a hint for post-processing.  (But it is only a hint because the child
+proces may be a shell script which doesn't have a session-id.)
++
+Note that the `t_rel` field contains the observed run time in seconds
+for the child process (starting before the fork/exec/spawn and
+stopping after the waitpid() and includes OS process creation overhead).
+So this time will be slightly larger than the atexit time reported by
+the child process itself.
+
+`"exec"`::
+	This event is generated before git attempts to `exec()`
+	another command rather than starting a child process.
++
+------------
+{
+	"event":"exec",
+	...
+	"exec_id":0,
+	"exe":"git",
+	"argv":["foo", "bar"]
+}
+------------
++
+The "exec_id" field is a command-unique id and is only useful if the
+`exec()` fails and a corresponding exec_result event is generated.
+
+`"exec_result"`::
+	This event is generated if the `exec()` fails and control
+	returns to the current git command.
++
+------------
+{
+	"event":"exec_result",
+	...
+	"exec_id":0,
+	"code":1      # error code (errno) from exec()
+}
+------------
+
+`"thread_start"`::
+	This event is generated when a thread is started.  It is
+	generated from *within* the new thread's thread-proc (for TLS
+	reasons).
++
+------------
+{
+	"event":"thread_start",
+	...
+	"thread":"th02:preload_thread" # thread name
+}
+------------
+
+`"thread_exit"`::
+	This event is generated when a thread exits.  It is generated
+	from *within* the thread's thread-proc (for TLS reasons).
++
+------------
+{
+	"event":"thread_exit",
+	...
+	"thread":"th02:preload_thread", # thread name
+	"t_rel":0.007328                # thread elapsed time
+}
+------------
+
+`"def_param"`::
+	This event is generated to log a global parameter.
++
+------------
+{
+	"event":"def_param",
+	...
+	"param":"core.abbrev",
+	"value":"7"
+}
+------------
+
+`"def_repo"`::
+	This event defines a repo-id and associates it with the root
+	of the worktree.
++
+------------
+{
+	"event":"def_repo",
+	...
+	"repo":1,
+	"worktree":"/Users/jeffhost/work/gfw"
+}
+------------
++
+As stated earlier, the repo-id is currently always 1, so there will
+only be one def_repo event.  Later, if in-proc submodules are
+supported, a def_repo event should be emitted for each submodule
+visited.
+
+`"region_enter"`::
+	This event is generated when entering a region.
++
+------------
+{
+	"event":"region_enter",
+	...
+	"repo":1,                # optional
+	"nesting":1,             # current region stack depth
+	"category":"index",      # optional
+	"label":"do_read_index", # optional
+	"msg":".git/index"       # optional
+}
+------------
++
+The `category` field may be used in a future enhancement to
+do category-based filtering.
++
+`GIT_TR2_EVENT_NESTING` or `trace2.eventNesting` can be used to
+filter deeply nested regions and data events.  It defaults to "2".
+
+`"region_leave"`::
+	This event is generated when leaving a region.
++
+------------
+{
+	"event":"region_leave",
+	...
+	"repo":1,                # optional
+	"t_rel":0.002876,        # time spent in region in seconds
+	"nesting":1,             # region stack depth
+	"category":"index",      # optional
+	"label":"do_read_index", # optional
+	"msg":".git/index"       # optional
+}
+------------
+
+`"data"`::
+	This event is generated to log a thread- and region-local
+	key/value pair.
++
+------------
+{
+	"event":"data",
+	...
+	"repo":1,              # optional
+	"t_abs":0.024107,      # absolute elapsed time
+	"t_rel":0.001031,      # elapsed time in region/thread
+	"nesting":2,           # region stack depth
+	"category":"index",
+	"key":"read/cache_nr",
+	"value":"3552"
+}
+------------
++
+The "value" field may be an integer or a string.
+
+`"data-json"`::
+	This event is generated to log a pre-formatted JSON string
+	containing structured data.
++
+------------
+{
+	"event":"data_json",
+	...
+	"repo":1,              # optional
+	"t_abs":0.015905,
+	"t_rel":0.015905,
+	"nesting":1,
+	"category":"process",
+	"key":"windows/ancestry",
+	"value":["bash.exe","bash.exe"]
+}
+------------
+
+== Example Trace2 API Usage
+
+Here is a hypothetical usage of the Trace2 API showing the intended
+usage (without worrying about the actual Git details).
+
+Initialization::
+
+	Initialization happens in `main()`.  Behind the scenes, an
+	`atexit` and `signal` handler are registered.
++
+----------------
+int main(int argc, const char **argv)
+{
+	int exit_code;
+
+	trace2_initialize();
+	trace2_cmd_start(argv);
+
+	exit_code = cmd_main(argc, argv);
+
+	trace2_cmd_exit(exit_code);
+
+	return exit_code;
+}
+----------------
+
+Command Details::
+
+	After the basics are established, additional command
+	information can be sent to Trace2 as it is discovered.
++
+----------------
+int cmd_checkout(int argc, const char **argv)
+{
+	trace2_cmd_name("checkout");
+	trace2_cmd_mode("branch");
+	trace2_def_repo(the_repository);
+
+	// emit "def_param" messages for "interesting" config settings.
+	trace2_cmd_list_config();
+
+	if (do_something())
+	    trace2_cmd_error("Path '%s': cannot do something", path);
+
+	return 0;
+}
+----------------
+
+Child Processes::
+
+	Wrap code spawning child processes.
++
+----------------
+void run_child(...)
+{
+	int child_exit_code;
+	struct child_process cmd = CHILD_PROCESS_INIT;
+	...
+	cmd.trace2_child_class = "editor";
+
+	trace2_child_start(&cmd);
+	child_exit_code = spawn_child_and_wait_for_it();
+	trace2_child_exit(&cmd, child_exit_code);
+}
+----------------
++
+For example, the following fetch command spawned ssh, index-pack,
+rev-list, and gc.  This example also shows that fetch took
+5.199 seconds and of that 4.932 was in ssh.
++
+----------------
+$ export GIT_TR2_BRIEF=1
+$ export GIT_TR2=~/log.normal
+$ git fetch origin
+...
+----------------
++
+----------------
+$ cat ~/log.normal
+version 2.20.1.vfs.1.1.47.g534dbe1ad1
+start git fetch origin
+worktree /Users/jeffhost/work/gfw
+cmd_name fetch (fetch)
+child_start[0] ssh git@github.com ...
+child_start[1] git index-pack ...
+... (Trace2 events from child processes omitted)
+child_exit[1] pid:14707 code:0 elapsed:0.076353
+child_exit[0] pid:14706 code:0 elapsed:4.931869
+child_start[2] git rev-list ...
+... (Trace2 events from child process omitted)
+child_exit[2] pid:14708 code:0 elapsed:0.110605
+child_start[3] git gc --auto
+... (Trace2 events from child process omitted)
+child_exit[3] pid:14709 code:0 elapsed:0.006240
+exit elapsed:5.198503 code:0
+atexit elapsed:5.198541 code:0
+----------------
++
+When a git process is a (direct or indirect) child of another
+git process, it inherits Trace2 context information.  This
+allows the child to print the command hierarchy.  This example
+shows gc as child[3] of fetch.  When the gc process reports
+its name as "gc", it also reports the hierarchy as "fetch/gc".
+(In this example, trace2 messages from the child process is
+indented for clarity.)
++
+----------------
+$ export GIT_TR2_BRIEF=1
+$ export GIT_TR2=~/log.normal
+$ git fetch origin
+...
+----------------
++
+----------------
+$ cat ~/log.normal
+version 2.20.1.160.g5676107ecd.dirty
+start git fetch official
+worktree /Users/jeffhost/work/gfw
+cmd_name fetch (fetch)
+...
+child_start[3] git gc --auto
+    version 2.20.1.160.g5676107ecd.dirty
+    start /Users/jeffhost/work/gfw/git gc --auto
+    worktree /Users/jeffhost/work/gfw
+    cmd_name gc (fetch/gc)
+    exit elapsed:0.001959 code:0
+    atexit elapsed:0.001997 code:0
+child_exit[3] pid:20303 code:0 elapsed:0.007564
+exit elapsed:3.868938 code:0
+atexit elapsed:3.868970 code:0
+----------------
+
+Regions::
+
+	Regions can be use to time an interesting section of code.
++
+----------------
+void wt_status_collect(struct wt_status *s)
+{
+	trace2_region_enter("status", "worktrees", s->repo);
+	wt_status_collect_changes_worktree(s);
+	trace2_region_leave("status", "worktrees", s->repo);
+
+	trace2_region_enter("status", "index", s->repo);
+	wt_status_collect_changes_index(s);
+	trace2_region_leave("status", "index", s->repo);
+
+	trace2_region_enter("status", "untracked", s->repo);
+	wt_status_collect_untracked(s);
+	trace2_region_leave("status", "untracked", s->repo);
+}
+
+void wt_status_print(struct wt_status *s)
+{
+	trace2_region_enter("status", "print", s->repo);
+	switch (s->status_format) {
+	    ...
+	}
+	trace2_region_leave("status", "print", s->repo);
+}
+----------------
++
+In this example, scanning for untracked files ran from +0.012568 to
++0.027149 (since the process started) and took 0.014581 seconds.
++
+----------------
+$ export GIT_TR2_PERF_BRIEF=1
+$ export GIT_TR2_PERF=~/log.perf
+$ git status
+...
+
+$ cat ~/log.perf
+d0 | main                     | version      |     |           |           |            | 2.20.1.160.g5676107ecd.dirty
+d0 | main                     | start        |     |  0.001173 |           |            | git status
+d0 | main                     | def_repo     | r1  |           |           |            | worktree:/Users/jeffhost/work/gfw
+d0 | main                     | cmd_name     |     |           |           |            | status (status)
+...
+d0 | main                     | region_enter | r1  |  0.010988 |           | status     | label:worktrees
+d0 | main                     | region_leave | r1  |  0.011236 |  0.000248 | status     | label:worktrees
+d0 | main                     | region_enter | r1  |  0.011260 |           | status     | label:index
+d0 | main                     | region_leave | r1  |  0.012542 |  0.001282 | status     | label:index
+d0 | main                     | region_enter | r1  |  0.012568 |           | status     | label:untracked
+d0 | main                     | region_leave | r1  |  0.027149 |  0.014581 | status     | label:untracked
+d0 | main                     | region_enter | r1  |  0.027411 |           | status     | label:print
+d0 | main                     | region_leave | r1  |  0.028741 |  0.001330 | status     | label:print
+d0 | main                     | exit         |     |  0.028778 |           |            | code:0
+d0 | main                     | atexit       |     |  0.028809 |           |            | code:0
+----------------
++
+Regions may be nested.  This causes messages to be indented in the
+PERF target, for example.
+Elapsed times are relative to the start of the correpsonding nesting
+level as expected.  For example, if we add region message to:
++
+----------------
+static enum path_treatment read_directory_recursive(struct dir_struct *dir,
+	struct index_state *istate, const char *base, int baselen,
+	struct untracked_cache_dir *untracked, int check_only,
+	int stop_at_first_file, const struct pathspec *pathspec)
+{
+	enum path_treatment state, subdir_state, dir_state = path_none;
+
+	trace2_region_enter_printf("dir", "read_recursive", NULL, "%.*s", baselen, base);
+	...
+	trace2_region_leave_printf("dir", "read_recursive", NULL, "%.*s", baselen, base);
+	return dir_state;
+}
+----------------
++
+We can further investigate the time spent scanning for untracked files.
++
+----------------
+$ export GIT_TR2_PERF_BRIEF=1
+$ export GIT_TR2_PERF=~/log.perf
+$ git status
+...
+$ cat ~/log.perf
+d0 | main                     | version      |     |           |           |            | 2.20.1.162.gb4ccea44db.dirty
+d0 | main                     | start        |     |  0.001173 |           |            | git status
+d0 | main                     | def_repo     | r1  |           |           |            | worktree:/Users/jeffhost/work/gfw
+d0 | main                     | cmd_name     |     |           |           |            | status (status)
+...
+d0 | main                     | region_enter | r1  |  0.015047 |           | status     | label:untracked
+d0 | main                     | region_enter |     |  0.015132 |           | dir        | ..label:read_recursive
+d0 | main                     | region_enter |     |  0.016341 |           | dir        | ....label:read_recursive vcs-svn/
+d0 | main                     | region_leave |     |  0.016422 |  0.000081 | dir        | ....label:read_recursive vcs-svn/
+d0 | main                     | region_enter |     |  0.016446 |           | dir        | ....label:read_recursive xdiff/
+d0 | main                     | region_leave |     |  0.016522 |  0.000076 | dir        | ....label:read_recursive xdiff/
+d0 | main                     | region_enter |     |  0.016612 |           | dir        | ....label:read_recursive git-gui/
+d0 | main                     | region_enter |     |  0.016698 |           | dir        | ......label:read_recursive git-gui/po/
+d0 | main                     | region_enter |     |  0.016810 |           | dir        | ........label:read_recursive git-gui/po/glossary/
+d0 | main                     | region_leave |     |  0.016863 |  0.000053 | dir        | ........label:read_recursive git-gui/po/glossary/
+...
+d0 | main                     | region_enter |     |  0.031876 |           | dir        | ....label:read_recursive builtin/
+d0 | main                     | region_leave |     |  0.032270 |  0.000394 | dir        | ....label:read_recursive builtin/
+d0 | main                     | region_leave |     |  0.032414 |  0.017282 | dir        | ..label:read_recursive
+d0 | main                     | region_leave | r1  |  0.032454 |  0.017407 | status     | label:untracked
+...
+d0 | main                     | exit         |     |  0.034279 |           |            | code:0
+d0 | main                     | atexit       |     |  0.034322 |           |            | code:0
+----------------
++
+Trace2 regions are similar to the existing trace_performance_enter()
+and trace_performance_leave() routines, but are thread safe and
+maintain per-thread stacks of timers.
+
+Data Messages::
+
+	Data messages added to a region.
++
+----------------
+int read_index_from(struct index_state *istate, const char *path,
+	const char *gitdir)
+{
+	trace2_region_enter_printf("index", "do_read_index", the_repository, "%s", path);
+
+	...
+
+	trace2_data_intmax("index", the_repository, "read/version", istate->version);
+	trace2_data_intmax("index", the_repository, "read/cache_nr", istate->cache_nr);
+
+	trace2_region_leave_printf("index", "do_read_index", the_repository, "%s", path);
+}
+----------------
++
+This example shows that the index contained 3552 entries.
++
+----------------
+$ export GIT_TR2_PERF_BRIEF=1
+$ export GIT_TR2_PERF=~/log.perf
+$ git status
+...
+$ cat ~/log.perf
+d0 | main                     | version      |     |           |           |            | 2.20.1.156.gf9916ae094.dirty
+d0 | main                     | start        |     |  0.001173 |           |            | git status
+d0 | main                     | def_repo     | r1  |           |           |            | worktree:/Users/jeffhost/work/gfw
+d0 | main                     | cmd_name     |     |           |           |            | status (status)
+d0 | main                     | region_enter | r1  |  0.001791 |           | index      | label:do_read_index .git/index
+d0 | main                     | data         | r1  |  0.002494 |  0.000703 | index      | ..read/version:2
+d0 | main                     | data         | r1  |  0.002520 |  0.000729 | index      | ..read/cache_nr:3552
+d0 | main                     | region_leave | r1  |  0.002539 |  0.000748 | index      | label:do_read_index .git/index
+...
+----------------
+
+Thread Events::
+
+	Thread messages added to a thread-proc.
++
+For example, the multithreaded preload-index code can be
+instrumented with a region around the thread pool and then
+per-thread start and exit events within the threadproc.
++
+----------------
+static void *preload_thread(void *_data)
+{
+	// start the per-thread clock and emit a message.
+	trace2_thread_start("preload_thread");
+
+	// report which chunk of the array this thread was assigned.
+	trace2_data_intmax("index", the_repository, "offset", p->offset);
+	trace2_data_intmax("index", the_repository, "count", nr);
+
+	do {
+	    ...
+	} while (--nr > 0);
+	...
+
+	// report elapsed time taken by this thread.
+	trace2_thread_exit();
+	return NULL;
+}
+
+void preload_index(struct index_state *index,
+	const struct pathspec *pathspec,
+	unsigned int refresh_flags)
+{
+	trace2_region_enter("index", "preload", the_repository);
+
+	for (i = 0; i < threads; i++) {
+	    ... /* create thread */
+	}
+
+	for (i = 0; i < threads; i++) {
+	    ... /* join thread */
+	}
+
+	trace2_region_leave("index", "preload", the_repository);
+}
+----------------
++
+In this example preload_index() was executed by the `main` thread
+and started the `preload` region.  Seven threads, named
+`th01:preload_thread` through `th07:preload_thread`, were started.
+Events from each thread are atomically appended to the shared target
+stream as they occur so they may appear in random order with respect
+other threads. Finally, the main thread waits for the threads to
+finish and leaves the region.
++
+Data events are tagged with the active thread name.  They are used
+to report the per-thread parameters.
++
+----------------
+$ export GIT_TR2_PERF_BRIEF=1
+$ export GIT_TR2_PERF=~/log.perf
+$ git status
+...
+$ cat ~/log.perf
+...
+d0 | main                     | region_enter | r1  |  0.002595 |           | index      | label:preload
+d0 | th01:preload_thread      | thread_start |     |  0.002699 |           |            |
+d0 | th02:preload_thread      | thread_start |     |  0.002721 |           |            |
+d0 | th01:preload_thread      | data         | r1  |  0.002736 |  0.000037 | index      | offset:0
+d0 | th02:preload_thread      | data         | r1  |  0.002751 |  0.000030 | index      | offset:2032
+d0 | th03:preload_thread      | thread_start |     |  0.002711 |           |            |
+d0 | th06:preload_thread      | thread_start |     |  0.002739 |           |            |
+d0 | th01:preload_thread      | data         | r1  |  0.002766 |  0.000067 | index      | count:508
+d0 | th06:preload_thread      | data         | r1  |  0.002856 |  0.000117 | index      | offset:2540
+d0 | th03:preload_thread      | data         | r1  |  0.002824 |  0.000113 | index      | offset:1016
+d0 | th04:preload_thread      | thread_start |     |  0.002710 |           |            |
+d0 | th02:preload_thread      | data         | r1  |  0.002779 |  0.000058 | index      | count:508
+d0 | th06:preload_thread      | data         | r1  |  0.002966 |  0.000227 | index      | count:508
+d0 | th07:preload_thread      | thread_start |     |  0.002741 |           |            |
+d0 | th07:preload_thread      | data         | r1  |  0.003017 |  0.000276 | index      | offset:3048
+d0 | th05:preload_thread      | thread_start |     |  0.002712 |           |            |
+d0 | th05:preload_thread      | data         | r1  |  0.003067 |  0.000355 | index      | offset:1524
+d0 | th05:preload_thread      | data         | r1  |  0.003090 |  0.000378 | index      | count:508
+d0 | th07:preload_thread      | data         | r1  |  0.003037 |  0.000296 | index      | count:504
+d0 | th03:preload_thread      | data         | r1  |  0.002971 |  0.000260 | index      | count:508
+d0 | th04:preload_thread      | data         | r1  |  0.002983 |  0.000273 | index      | offset:508
+d0 | th04:preload_thread      | data         | r1  |  0.007311 |  0.004601 | index      | count:508
+d0 | th05:preload_thread      | thread_exit  |     |  0.008781 |  0.006069 |            |
+d0 | th01:preload_thread      | thread_exit  |     |  0.009561 |  0.006862 |            |
+d0 | th03:preload_thread      | thread_exit  |     |  0.009742 |  0.007031 |            |
+d0 | th06:preload_thread      | thread_exit  |     |  0.009820 |  0.007081 |            |
+d0 | th02:preload_thread      | thread_exit  |     |  0.010274 |  0.007553 |            |
+d0 | th07:preload_thread      | thread_exit  |     |  0.010477 |  0.007736 |            |
+d0 | th04:preload_thread      | thread_exit  |     |  0.011657 |  0.008947 |            |
+d0 | main                     | region_leave | r1  |  0.011717 |  0.009122 | index      | label:preload
+...
+d0 | main                     | exit         |     |  0.029996 |           |            | code:0
+d0 | main                     | atexit       |     |  0.030027 |           |            | code:0
+----------------
++
+In this example, the preload region took 0.009122 seconds.  The 7 threads
+took between 0.006069 and 0.008947 seconds to work on their portion of
+the index.  Thread "th01" worked on 508 items at offset 0.  Thread "th02"
+worked on 508 items at offset 2032.  Thread "th04" worked on 508 itemts
+at offset 508.
++
+This example also shows that thread names are assigned in a racy manner
+as each thread starts and allocates TLS storage.
+
+== Future Work
+
+=== Relationship to the Existing Trace Api (api-trace.txt)
+
+There are a few issues to resolve before we can completely
+switch to Trace2.
+
+* Updating existing tests that assume GIT_TRACE format messages.
+
+* How to best handle custom GIT_TRACE_<key> messages?
+
+** The GIT_TRACE_<key> mechanism allows each <key> to write to a
+different file (in addition to just stderr).
+
+** Do we want to maintain that ability or simply write to the existing
+Trace2 targets (and convert <key> to a "category").
diff --git a/Documentation/technical/read-object-protocol.txt b/Documentation/technical/read-object-protocol.txt
new file mode 100644
index 00000000000000..a893b46e7c28a9
--- /dev/null
+++ b/Documentation/technical/read-object-protocol.txt
@@ -0,0 +1,102 @@
+Read Object Process
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The read-object process enables Git to read all missing blobs with a
+single process invocation for the entire life of a single Git command.
+This is achieved by using a packet format (pkt-line, see technical/
+protocol-common.txt) based protocol over standard input and standard
+output as follows. All packets, except for the "*CONTENT" packets and
+the "0000" flush packet, are considered text and therefore are
+terminated by a LF.
+
+Git starts the process when it encounters the first missing object that
+needs to be retrieved. After the process is started, Git sends a welcome
+message ("git-read-object-client"), a list of supported protocol version
+numbers, and a flush packet. Git expects to read a welcome response
+message ("git-read-object-server"), exactly one protocol version number
+from the previously sent list, and a flush packet. All further
+communication will be based on the selected version.
+
+The remaining protocol description below documents "version=1". Please
+note that "version=42" in the example below does not exist and is only
+there to illustrate how the protocol would look with more than one
+version.
+
+After the version negotiation Git sends a list of all capabilities that
+it supports and a flush packet. Git expects to read a list of desired
+capabilities, which must be a subset of the supported capabilities list,
+and a flush packet as response:
+------------------------
+packet: git> git-read-object-client
+packet: git> version=1
+packet: git> version=42
+packet: git> 0000
+packet: git< git-read-object-server
+packet: git< version=1
+packet: git< 0000
+packet: git> capability=get
+packet: git> capability=have
+packet: git> capability=put
+packet: git> capability=not-yet-invented
+packet: git> 0000
+packet: git< capability=get
+packet: git< 0000
+------------------------
+The only supported capability in version 1 is "get".
+
+Afterwards Git sends a list of "key=value" pairs terminated with a flush
+packet. The list will contain at least the command (based on the
+supported capabilities) and the sha1 of the object to retrieve. Please
+note, that the process must not send any response before it received the
+final flush packet.
+
+When the process receives the "get" command, it should make the requested
+object available in the git object store and then return success. Git will
+then check the object store again and this time find it and proceed.
+------------------------
+packet: git> command=get
+packet: git> sha1=0a214a649e1b3d5011e14a3dc227753f2bd2be05
+packet: git> 0000
+------------------------
+
+The process is expected to respond with a list of "key=value" pairs
+terminated with a flush packet. If the process does not experience
+problems then the list must contain a "success" status.
+------------------------
+packet: git< status=success
+packet: git< 0000
+------------------------
+
+In case the process cannot or does not want to process the content, it
+is expected to respond with an "error" status.
+------------------------
+packet: git< status=error
+packet: git< 0000
+------------------------
+
+In case the process cannot or does not want to process the content as
+well as any future content for the lifetime of the Git process, then it
+is expected to respond with an "abort" status at any point in the
+protocol.
+------------------------
+packet: git< status=abort
+packet: git< 0000
+------------------------
+
+Git neither stops nor restarts the process in case the "error"/"abort"
+status is set.
+
+If the process dies during the communication or does not adhere to the
+protocol then Git will stop the process and restart it with the next
+object that needs to be processed.
+
+After the read-object process has processed an object it is expected to
+wait for the next "key=value" list containing a command. Git will close
+the command pipe on exit. The process is expected to detect EOF and exit
+gracefully on its own. Git will wait until the process has stopped.
+
+A long running read-object process demo implementation can be found in
+`contrib/long-running-read-object/example.pl` located in the Git core
+repository. If you develop your own long running process then the
+`GIT_TRACE_PACKET` environment variables can be very helpful for
+debugging (see linkgit:git[1]).
diff --git a/Documentation/technical/status-serialization-format.txt b/Documentation/technical/status-serialization-format.txt
new file mode 100644
index 00000000000000..475ae814495581
--- /dev/null
+++ b/Documentation/technical/status-serialization-format.txt
@@ -0,0 +1,107 @@
+Git status serialization format
+===============================
+
+Git status serialization enables git to dump the results of a status scan
+to a binary file.  This file can then be loaded by later status invocations
+to print the cached status results.
+
+The file contains the essential fields from:
+() the index
+() the "struct wt_status" for the overall results
+() the contents of "struct wt_status_change_data" for tracked changed files
+() the list of untracked and ignored files
+
+Version 1 Format:
+=================
+
+The V1 file begins with a required header section followed by optional
+sections for each type of item (changed, untracked, ignored).  Individual
+item sections are only present if necessary.  Each item section begins
+with an item-type header with the number of items in the section.
+
+Each "line" in the format is encoded using pkt-line with a final LF.
+Flush packets are used to terminate sections.
+
+-----------------
+PKT-LINE("version" SP "1")
+<v1-header-section>
+[<v1-changed-item-section>]
+[<v1-untracked-item-section>]
+[<v1-ignored-item-section>]
+-----------------
+
+
+V1 Header
+---------
+
+The v1-header-section fields are taken directly from "struct wt_status".
+Each field is printed on a separate pkt-line.  Lines for NULL string
+values are omitted.  All integers are printed with "%d".  OIDs are
+printed in hex.
+
+v1-header-section    = <v1-index-headers>
+		       <v1-wt-status-headers>
+		       PKT-LINE(<flush>)
+
+v1-index-headers     = PKT-LINE("index_mtime" SP <sec> SP <nsec> LF)
+
+v1-wt-status-headers = PKT-LINE("is_initial" SP <integer> LF)
+		       [ PKT-LINE("branch" SP <branch-name> LF) ]
+		       [ PKT-LINE("reference" SP <reference-name> LF) ]
+		       PKT-LINE("show_ignored_files" SP <integer> LF)
+		       PKT-LINE("show_untracked_files" SP <integer> LF)
+		       PKT-LINE("show_ignored_directory" SP <integer> LF)
+		       [ PKT-LINE("ignore_submodule_arg" SP <string> LF) ]
+		       PKT-LINE("detect_rename" SP <integer> LF)
+		       PKT-LINE("rename_score" SP <integer> LF)
+		       PKT-LINE("rename_limit" SP <integer> LF)
+		       PKT-LINE("detect_break" SP <integer> LF)
+		       PKT-LINE("sha1_commit" SP <oid> LF)
+		       PKT-LINE("committable" SP <integer> LF)
+		       PKT-LINE("workdir_dirty" SP <integer> LF)
+
+
+V1 Changed Items
+----------------
+
+The v1-changed-item-section lists all of the changed items with one
+item per pkt-line.  Each pkt-line contains:  a binary block of data
+from "struct wt_status_serialize_data_fixed" in a fixed header where
+integers are in network byte order and OIDs are in raw (non-hex) form.
+This is followed by one or two raw pathnames (not c-quoted) with NUL
+terminators (both NULs are always present even if there is no rename).
+
+v1-changed-item-section = PKT-LINE("changed" SP <count> LF)
+			  [ PKT-LINE(<changed_item> LF) ]+
+			  PKT-LINE(<flush>)
+
+changed_item = <byte[4] worktree_status>
+	       <byte[4] index_status>
+	       <byte[4] stagemask>
+	       <byte[4] score>
+	       <byte[4] mode_head>
+	       <byte[4] mode_index>
+	       <byte[4] mode_worktree>
+	       <byte[4] dirty_submodule>
+	       <byte[4] new_submodule_commits>
+	       <byte[20] oid_head>
+	       <byte[20] oid_index>
+	       <byte[*] path>
+	       NUL
+	       [ <byte[*] src_path> ]
+	       NUL
+
+
+V1 Untracked and Ignored Items
+------------------------------
+
+These sections are simple lists of pathnames.  They ARE NOT
+c-quoted.
+
+v1-untracked-item-section = PKT-LINE("untracked" SP <count> LF)
+			    [ PKT-LINE(<pathname> LF) ]+
+			    PKT-LINE(<flush>)
+
+v1-ignored-item-section = PKT-LINE("ignored" SP <count> LF)
+			  [ PKT-LINE(<pathname> LF) ]+
+			  PKT-LINE(<flush>)
diff --git a/Documentation/trace2-target-values.txt b/Documentation/trace2-target-values.txt
new file mode 100644
index 00000000000000..27d3c64e6655de
--- /dev/null
+++ b/Documentation/trace2-target-values.txt
@@ -0,0 +1,10 @@
+--
+* `0` or `false` - Disables the target.
+* `1` or `true` - Writes to `STDERR`.
+* `[2-9]` - Writes to the already opened file descriptor.
+* `<absolute-pathname>` - Writes to the file in append mode.
+* `af_unix:[<socket_type>:]<absolute-pathname>` - Write to a
+Unix DomainSocket (on platforms that support them).  Socket
+type can be either `stream` or `dgram`; if omitted Git will
+try both.
+--
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 13f835f9cde4fd..d8e71cb60c9c39 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 GVF=GIT-VERSION-FILE
-DEF_VER=v2.21.0
+DEF_VER=v2.21.0.vfs.1.1
 
 LF='
 '
@@ -12,7 +12,7 @@ if test -f version
 then
 	VN=$(cat version) || VN="$DEF_VER"
 elif test -d ${GIT_DIR:-.git} -o -f .git &&
-	VN=$(git describe --match "v[0-9]*" HEAD 2>/dev/null) &&
+	VN=$(git describe --match "v[0-9]*vfs*" HEAD 2>/dev/null) &&
 	case "$VN" in
 	*$LF*) (exit 1) ;;
 	v[0-9]*)
diff --git a/Makefile b/Makefile
index 7b9668c1a747a8..a0b1f0d5293358 100644
--- a/Makefile
+++ b/Makefile
@@ -776,6 +776,7 @@ TEST_BUILTINS_OBJS += test-string-list.o
 TEST_BUILTINS_OBJS += test-submodule-config.o
 TEST_BUILTINS_OBJS += test-submodule-nested-repo-config.o
 TEST_BUILTINS_OBJS += test-subprocess.o
+TEST_BUILTINS_OBJS += test-trace2.o
 TEST_BUILTINS_OBJS += test-urlmatch-normalization.o
 TEST_BUILTINS_OBJS += test-xml-encode.o
 TEST_BUILTINS_OBJS += test-wildmatch.o
@@ -917,6 +918,7 @@ LIB_OBJS += gettext.o
 LIB_OBJS += gpg-interface.o
 LIB_OBJS += graph.o
 LIB_OBJS += grep.o
+LIB_OBJS += gvfs.o
 LIB_OBJS += hashmap.o
 LIB_OBJS += linear-assignment.o
 LIB_OBJS += help.o
@@ -1020,6 +1022,17 @@ LIB_OBJS += tempfile.o
 LIB_OBJS += thread-utils.o
 LIB_OBJS += tmp-objdir.o
 LIB_OBJS += trace.o
+LIB_OBJS += trace2.o
+LIB_OBJS += trace2/tr2_cfg.o
+LIB_OBJS += trace2/tr2_cmd_name.o
+LIB_OBJS += trace2/tr2_dst.o
+LIB_OBJS += trace2/tr2_sid.o
+LIB_OBJS += trace2/tr2_sysenv.o
+LIB_OBJS += trace2/tr2_tbuf.o
+LIB_OBJS += trace2/tr2_tgt_event.o
+LIB_OBJS += trace2/tr2_tgt_normal.o
+LIB_OBJS += trace2/tr2_tgt_perf.o
+LIB_OBJS += trace2/tr2_tls.o
 LIB_OBJS += trailer.o
 LIB_OBJS += transport.o
 LIB_OBJS += transport-helper.o
@@ -1036,6 +1049,7 @@ LIB_OBJS += utf8.o
 LIB_OBJS += varint.o
 LIB_OBJS += version.o
 LIB_OBJS += versioncmp.o
+LIB_OBJS += virtualfilesystem.o
 LIB_OBJS += walker.o
 LIB_OBJS += wildmatch.o
 LIB_OBJS += worktree.o
@@ -1043,6 +1057,8 @@ LIB_OBJS += wrapper.o
 LIB_OBJS += write-or-die.o
 LIB_OBJS += ws.o
 LIB_OBJS += wt-status.o
+LIB_OBJS += wt-status-deserialize.o
+LIB_OBJS += wt-status-serialize.o
 LIB_OBJS += xdiff-interface.o
 LIB_OBJS += zlib.o
 
@@ -1600,7 +1616,9 @@ ifdef NO_INET_PTON
 	LIB_OBJS += compat/inet_pton.o
 	BASIC_CFLAGS += -DNO_INET_PTON
 endif
-ifndef NO_UNIX_SOCKETS
+ifdef NO_UNIX_SOCKETS
+	BASIC_CFLAGS += -DNO_UNIX_SOCKETS
+else
 	LIB_OBJS += unix-socket.o
 	PROGRAM_OBJS += credential-cache.o
 	PROGRAM_OBJS += credential-cache--daemon.o
diff --git a/advice.c b/advice.c
index 567209aa79afee..b6f09947d2b7ac 100644
--- a/advice.c
+++ b/advice.c
@@ -12,6 +12,7 @@ int advice_push_needs_force = 1;
 int advice_push_unqualified_ref_name = 1;
 int advice_status_hints = 1;
 int advice_status_u_option = 1;
+int advice_status_ahead_behind_warning = 1;
 int advice_commit_before_merge = 1;
 int advice_reset_quiet_warning = 1;
 int advice_resolve_conflict = 1;
@@ -67,6 +68,7 @@ static struct {
 	{ "pushUnqualifiedRefName", &advice_push_unqualified_ref_name },
 	{ "statusHints", &advice_status_hints },
 	{ "statusUoption", &advice_status_u_option },
+	{ "statusAheadBehindWarning", &advice_status_ahead_behind_warning },
 	{ "commitBeforeMerge", &advice_commit_before_merge },
 	{ "resetQuiet", &advice_reset_quiet_warning },
 	{ "resolveConflict", &advice_resolve_conflict },
diff --git a/advice.h b/advice.h
index f875f8cd8da5fd..9dc9e491094de8 100644
--- a/advice.h
+++ b/advice.h
@@ -12,6 +12,7 @@ extern int advice_push_needs_force;
 extern int advice_push_unqualified_ref_name;
 extern int advice_status_hints;
 extern int advice_status_u_option;
+extern int advice_status_ahead_behind_warning;
 extern int advice_commit_before_merge;
 extern int advice_reset_quiet_warning;
 extern int advice_resolve_conflict;
diff --git a/apply.c b/apply.c
index 38283788b1772a..9add67802916cf 100644
--- a/apply.c
+++ b/apply.c
@@ -3349,6 +3349,24 @@ static int checkout_target(struct index_state *istate,
 {
 	struct checkout costate = CHECKOUT_INIT;
 
+	/*
+	 * Do not checkout the entry if the skipworktree bit is set
+	 *
+	 * Both callers of this method (check_preimage and load_current)
+	 * check for the existance of the file before calling this
+	 * method so we know that the file doesn't exist at this point
+	 * and we don't need to perform that check again here.
+	 * We just need to check the skip-worktree and return.
+	 *
+	 * This is to prevent git from creating a file in the
+	 * working directory that has the skip-worktree bit on,
+	 * then updating the index from the patch and not keeping
+	 * the working directory version up to date with what it
+	 * changed the index version to be.
+	 */
+	if (ce_skip_worktree(ce))
+		return 0;
+
 	costate.refresh_cache = 1;
 	costate.istate = istate;
 	if (checkout_entry(ce, &costate, NULL, NULL) ||
diff --git a/builtin/am.c b/builtin/am.c
index 58a2aef28bbcd7..cca494d9c3bac6 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -453,6 +453,7 @@ static int run_post_rewrite_hook(const struct am_state *state)
 
 	cp.in = xopen(am_path(state, "rewritten"), O_RDONLY);
 	cp.stdout_to_stderr = 1;
+	cp.trace2_hook_name = "post-rewrite";
 
 	ret = run_command(&cp);
 
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 702bc535d2b8ae..040690d3c25aed 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -263,6 +263,8 @@ static int checkout_paths(const struct checkout_opts *opts,
 	struct lock_file lock_file = LOCK_INIT;
 	int nr_checkouts = 0, nr_unmerged = 0;
 
+	trace2_cmd_mode(opts->patch_mode ? "patch" : "path");
+
 	if (opts->track != BRANCH_TRACK_UNSPECIFIED)
 		die(_("'%s' cannot be used with updating paths"), "--track");
 
@@ -854,8 +856,11 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 	remove_branch_state(the_repository);
 	strbuf_release(&msg);
 	if (!opts->quiet &&
-	    (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD"))))
+	    (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD")))) {
+		trace2_region_enter("exp", "report_tracking", the_repository);
 		report_tracking(new_branch_info);
+		trace2_region_leave("exp", "report_tracking", the_repository);
+	}
 }
 
 static int add_pending_uninteresting_ref(const char *refname,
@@ -968,6 +973,9 @@ static int switch_branches(const struct checkout_opts *opts,
 	void *path_to_free;
 	struct object_id rev;
 	int flag, writeout_error = 0;
+
+	trace2_cmd_mode("branch");
+
 	memset(&old_branch_info, 0, sizeof(old_branch_info));
 	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
 	if (old_branch_info.path)
@@ -1205,6 +1213,8 @@ static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
 	int status;
 	struct strbuf branch_ref = STRBUF_INIT;
 
+	trace2_cmd_mode("unborn");
+
 	if (!opts->new_branch)
 		die(_("You are on a branch yet to be born"));
 	strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
diff --git a/builtin/commit.c b/builtin/commit.c
index 8348694141cdd0..9152fd8edb236c 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -143,6 +143,116 @@ static int opt_parse_porcelain(const struct option *opt, const char *arg, int un
 	return 0;
 }
 
+static int do_serialize = 0;
+static char *serialize_path = NULL;
+
+static int reject_implicit = 0;
+static int do_implicit_deserialize = 0;
+static int do_explicit_deserialize = 0;
+static char *deserialize_path = NULL;
+
+static enum wt_status_deserialize_wait implicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+static enum wt_status_deserialize_wait explicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+
+/*
+ * --serialize | --serialize=<path>
+ *
+ * Request that we serialize status output rather than or in addition to
+ * printing in any of the established formats.
+ *
+ * Without a path, we write binary serialization data to stdout (and omit
+ * the normal status output).
+ *
+ * With a path, we write binary serialization data to the <path> and then
+ * write normal status output.
+ */
+static int opt_parse_serialize(const struct option *opt, const char *arg, int unset)
+{
+	enum wt_status_format *value = (enum wt_status_format *)opt->value;
+	if (unset || !arg)
+		*value = STATUS_FORMAT_SERIALIZE_V1;
+
+	if (arg) {
+		free(serialize_path);
+		serialize_path = xstrdup(arg);
+	}
+
+	if (do_explicit_deserialize)
+		die("cannot mix --serialize and --deserialize");
+	do_implicit_deserialize = 0;
+
+	do_serialize = 1;
+	return 0;
+}
+
+/*
+ * --deserialize | --deserialize=<path> |
+ * --no-deserialize
+ *
+ * Request that we deserialize status data from some existing resource
+ * rather than performing a status scan.
+ *
+ * The input source can come from stdin or a path given here -- or be
+ * inherited from the config settings.
+ */
+static int opt_parse_deserialize(const struct option *opt, const char *arg, int unset)
+{
+	if (unset) {
+		do_implicit_deserialize = 0;
+		do_explicit_deserialize = 0;
+	} else {
+		if (do_serialize)
+			die("cannot mix --serialize and --deserialize");
+		if (arg) {
+			/* override config or stdin */
+			free(deserialize_path);
+			deserialize_path = xstrdup(arg);
+		}
+		if (deserialize_path && *deserialize_path
+		    && (wt_status_deserialize_access(deserialize_path, R_OK) != 0))
+			die("cannot find serialization file '%s'",
+			    deserialize_path);
+
+		do_explicit_deserialize = 1;
+	}
+
+	return 0;
+}
+
+static enum wt_status_deserialize_wait parse_dw(const char *arg)
+{
+	int tenths;
+
+	if (!strcmp(arg, "fail"))
+		return DESERIALIZE_WAIT__FAIL;
+	else if (!strcmp(arg, "block"))
+		return DESERIALIZE_WAIT__BLOCK;
+	else if (!strcmp(arg, "no"))
+		return DESERIALIZE_WAIT__NO;
+
+	/*
+	 * Otherwise, assume it is a timeout in tenths of a second.
+	 * If it contains a bogus value, atol() will return zero
+	 * which is OK.
+	 */
+	tenths = atol(arg);
+	if (tenths < 0)
+		tenths = DESERIALIZE_WAIT__NO;
+	return tenths;
+}
+
+static int opt_parse_deserialize_wait(const struct option *opt,
+				      const char *arg,
+				      int unset)
+{
+	if (unset)
+		explicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+	else
+		explicit_deserialize_wait = parse_dw(arg);
+
+	return 0;
+}
+
 static int opt_parse_m(const struct option *opt, const char *arg, int unset)
 {
 	struct strbuf *buf = opt->value;
@@ -1038,6 +1148,8 @@ static void handle_untracked_files_arg(struct wt_status *s)
 		s->show_untracked_files = SHOW_NORMAL_UNTRACKED_FILES;
 	else if (!strcmp(untracked_files_arg, "all"))
 		s->show_untracked_files = SHOW_ALL_UNTRACKED_FILES;
+	else if (!strcmp(untracked_files_arg,"complete"))
+		s->show_untracked_files = SHOW_COMPLETE_UNTRACKED_FILES;
 	else
 		die(_("Invalid untracked files mode '%s'"), untracked_files_arg);
 }
@@ -1061,9 +1173,11 @@ static const char *read_commit_message(const char *name)
 static struct status_deferred_config {
 	enum wt_status_format status_format;
 	int show_branch;
+	enum ahead_behind_flags ahead_behind;
 } status_deferred_config = {
 	STATUS_FORMAT_UNSPECIFIED,
-	-1 /* unspecified */
+	-1, /* unspecified */
+	AHEAD_BEHIND_UNSPECIFIED,
 };
 
 static void finalize_deferred_config(struct wt_status *s)
@@ -1090,6 +1204,17 @@ static void finalize_deferred_config(struct wt_status *s)
 	if (s->show_branch < 0)
 		s->show_branch = 0;
 
+	/*
+	 * If the user did not give a "--[no]-ahead-behind" command
+	 * line argument *AND* we will print in a human-readable format
+	 * (short, long etc.) then we inherit from the status.aheadbehind
+	 * config setting.  In all other cases (and porcelain V[12] formats
+	 * in particular), we inherit _FULL for backwards compatibility.
+	 */
+	if (use_deferred_config &&
+	    s->ahead_behind_flags == AHEAD_BEHIND_UNSPECIFIED)
+		s->ahead_behind_flags = status_deferred_config.ahead_behind;
+
 	if (s->ahead_behind_flags == AHEAD_BEHIND_UNSPECIFIED)
 		s->ahead_behind_flags = AHEAD_BEHIND_FULL;
 }
@@ -1241,6 +1366,10 @@ static int git_status_config(const char *k, const char *v, void *cb)
 		status_deferred_config.show_branch = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "status.aheadbehind")) {
+		status_deferred_config.ahead_behind = git_config_bool(k, v);
+		return 0;
+	}
 	if (!strcmp(k, "status.showstash")) {
 		s->show_stash = git_config_bool(k, v);
 		return 0;
@@ -1266,6 +1395,28 @@ static int git_status_config(const char *k, const char *v, void *cb)
 		s->relative_paths = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "status.deserializepath")) {
+		/*
+		 * Automatically assume deserialization if this is
+		 * set in the config and the file exists.  Do not
+		 * complain if the file does not exist, because we
+		 * silently fall back to normal mode.
+		 */
+		if (v && *v && access(v, R_OK) == 0) {
+			do_implicit_deserialize = 1;
+			deserialize_path = xstrdup(v);
+		} else {
+			reject_implicit = 1;
+		}
+		return 0;
+	}
+	if (!strcmp(k, "status.deserializewait")) {
+		if (!v || !*v)
+			implicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+		else
+			implicit_deserialize_wait = parse_dw(v);
+		return 0;
+	}
 	if (!strcmp(k, "status.showuntrackedfiles")) {
 		if (!v)
 			return config_error_nonbool(k);
@@ -1308,7 +1459,8 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	static int show_ignored_directory = 0;
 	static struct wt_status s;
 	unsigned int progress_flag = 0;
-	int fd;
+	int try_deserialize;
+	int fd = -1;
 	struct object_id oid;
 	static struct option builtin_status_options[] = {
 		OPT__VERBOSE(&verbose, N_("be verbose")),
@@ -1323,6 +1475,15 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 		{ OPTION_CALLBACK, 0, "porcelain", &status_format,
 		  N_("version"), N_("machine-readable output"),
 		  PARSE_OPT_OPTARG, opt_parse_porcelain },
+		{ OPTION_CALLBACK, 0, "serialize", &status_format,
+		  N_("path"), N_("serialize raw status data to path or stdout"),
+		  PARSE_OPT_OPTARG | PARSE_OPT_NONEG, opt_parse_serialize },
+		{ OPTION_CALLBACK, 0, "deserialize", NULL,
+		  N_("path"), N_("deserialize raw status data from file"),
+		  PARSE_OPT_OPTARG, opt_parse_deserialize },
+		{ OPTION_CALLBACK, 0, "deserialize-wait", NULL,
+		  N_("fail|block|no"), N_("how to wait if status cache file is invalid"),
+		  PARSE_OPT_OPTARG, opt_parse_deserialize_wait },
 		OPT_SET_INT(0, "long", &status_format,
 			    N_("show status in long format (default)"),
 			    STATUS_FORMAT_LONG),
@@ -1383,10 +1544,37 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	    s.show_untracked_files == SHOW_NO_UNTRACKED_FILES)
 		die(_("Unsupported combination of ignored and untracked-files arguments"));
 
+	if (s.show_untracked_files == SHOW_COMPLETE_UNTRACKED_FILES &&
+	    s.show_ignored_mode == SHOW_NO_IGNORED)
+		die(_("Complete Untracked only supported with ignored files"));
+
 	parse_pathspec(&s.pathspec, 0,
 		       PATHSPEC_PREFER_FULL,
 		       prefix, argv);
 
+	/*
+	 * If we want to try to deserialize status data from a cache file,
+	 * we need to re-order the initialization code.  The problem is that
+	 * this makes for a very nasty diff and causes merge conflicts as we
+	 * carry it forward.  And it easy to mess up the merge, so we
+	 * duplicate some code here to hopefully reduce conflicts.
+	 */
+	try_deserialize = (!do_serialize &&
+			   (do_implicit_deserialize || do_explicit_deserialize));
+	if (try_deserialize)
+		goto skip_init;
+	/*
+	 * If we implicitly received a status cache pathname from the config
+	 * and the file does not exist, we silently reject it and do the normal
+	 * status "collect".  Fake up some trace2 messages to reflect this and
+	 * assist post-processors know this case is different.
+	 */
+	if (!do_serialize && reject_implicit) {
+		trace2_cmd_mode("implicit-deserialize");
+		trace2_data_string("status", the_repository, "deserialize/reject",
+				   "status-cache/access");
+	}
+
 	enable_fscache(0);
 	if (status_format != STATUS_FORMAT_PORCELAIN &&
 	    status_format != STATUS_FORMAT_PORCELAIN_V2)
@@ -1401,6 +1589,7 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	else
 		fd = -1;
 
+skip_init:
 	s.is_initial = get_oid(s.reference, &oid) ? 1 : 0;
 	if (!s.is_initial)
 		hashcpy(s.sha1_commit, oid.hash);
@@ -1417,6 +1606,36 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 			s.rename_score = parse_rename_score(&rename_score_arg);
 	}
 
+	if (try_deserialize) {
+		int result;
+		enum wt_status_deserialize_wait dw = implicit_deserialize_wait;
+		if (explicit_deserialize_wait != DESERIALIZE_WAIT__UNSET)
+			dw = explicit_deserialize_wait;
+		if (dw == DESERIALIZE_WAIT__UNSET)
+			dw = DESERIALIZE_WAIT__NO;
+
+		if (s.relative_paths)
+			s.prefix = prefix;
+
+		trace2_cmd_mode("deserialize");
+		result = wt_status_deserialize(&s, deserialize_path, dw);
+		if (result == DESERIALIZE_OK)
+			return 0;
+		if (dw == DESERIALIZE_WAIT__FAIL)
+			die(_("Rejected status serialization cache"));
+
+		/* deserialize failed, so force the initialization we skipped above. */
+		enable_fscache(1);
+		read_cache_preload(&s.pathspec);
+		refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, &s.pathspec, NULL, NULL);
+
+		if (use_optional_locks())
+			fd = hold_locked_index(&index_lock, 0);
+		else
+			fd = -1;
+	}
+
+	trace2_cmd_mode("collect");
 	wt_status_collect(&s);
 
 	if (0 <= fd)
@@ -1425,6 +1644,17 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	if (s.relative_paths)
 		s.prefix = prefix;
 
+	if (serialize_path) {
+		int fd_serialize = xopen(serialize_path,
+					 O_WRONLY | O_CREAT | O_TRUNC, 0666);
+		if (fd_serialize < 0)
+			die_errno(_("could not serialize to '%s'"),
+				  serialize_path);
+		trace2_cmd_mode("serialize");
+		wt_status_serialize_v1(fd_serialize, &s);
+		close(fd_serialize);
+	}
+
 	wt_status_print(&s);
 	wt_status_collect_free_buffers(&s);
 
diff --git a/builtin/fetch.c b/builtin/fetch.c
index b620fd54b4e95c..ba7187dd7a5d58 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -24,6 +24,8 @@
 #include "list-objects-filter-options.h"
 #include "commit-reach.h"
 
+#define FORCED_UPDATES_DELAY_WARNING_IN_MS (10 * 1000)
+
 static const char * const builtin_fetch_usage[] = {
 	N_("git fetch [<options>] [<repository> [<refspec>...]]"),
 	N_("git fetch [<options>] <group>"),
@@ -39,6 +41,9 @@ enum {
 };
 
 static int fetch_prune_config = -1; /* unspecified */
+static int fetch_show_forced_updates = 1;
+static int fetch_show_forced_updates_warning = 0;
+static uint64_t forced_updates_ms = 0;
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
@@ -79,6 +84,11 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.showforcedupdates")) {
+		fetch_show_forced_updates = git_config_bool(k, v);
+		return 0;
+	}
+
 	if (!strcmp(k, "submodule.recurse")) {
 		int r = git_config_bool(k, v) ?
 			RECURSE_SUBMODULES_ON : RECURSE_SUBMODULES_OFF;
@@ -169,6 +179,8 @@ static struct option builtin_fetch_options[] = {
 	OPT_STRING_LIST(0, "negotiation-tip", &negotiation_tip, N_("revision"),
 			N_("report that we have only objects reachable from this object")),
 	OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
+	OPT_BOOL(0, "show-forced-updates", &fetch_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 	OPT_END()
 };
 
@@ -699,6 +711,7 @@ static int update_local_ref(struct ref *ref,
 	enum object_type type;
 	struct branch *current_branch = branch_get(NULL);
 	const char *pretty_ref = prettify_refname(ref->name);
+	int fast_forward = 0;
 
 	type = oid_object_info(the_repository, &ref->new_oid, NULL);
 	if (type < 0)
@@ -773,9 +786,19 @@ static int update_local_ref(struct ref *ref,
 		return r;
 	}
 
-	if (in_merge_bases(current, updated)) {
+	if (fetch_show_forced_updates) {
+		uint64_t t_before = getnanotime();
+		fast_forward = in_merge_bases(current, updated);
+		forced_updates_ms += (getnanotime() - t_before) / 1000000;
+	} else {
+		fetch_show_forced_updates_warning = 1;
+		fast_forward = 1;
+	}
+
+	if (fast_forward) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
+
 		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
 		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
@@ -971,6 +994,17 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 		      " 'git remote prune %s' to remove any old, conflicting "
 		      "branches"), remote_name);
 
+	if (!fetch_show_forced_updates && fetch_show_forced_updates_warning) {
+		warning(_("Fetch normally indicates which branches had a forced update, but that check has been disabled."));
+		warning(_("To re-enable, use '--show-forced-updates' flag or run 'git config fetch.showForcedUpdates true'."));
+	}
+	if (fetch_show_forced_updates &&
+	    forced_updates_ms > FORCED_UPDATES_DELAY_WARNING_IN_MS) {
+		warning(_("It took %.2f seconds to check forced updates. You can use '--no-show-forced-updates'\n"),
+			forced_updates_ms / 1000.0);
+		warning(_("or run 'git config fetch.showForcedUpdates false' to avoid this check.\n"));
+	}
+
  abort:
 	strbuf_release(&note);
 	free(url);
@@ -1556,7 +1590,9 @@ static int fetch_one(struct remote *remote, int argc, const char **argv, int pru
 
 	sigchain_push_common(unlock_pack_on_signal);
 	atexit(unlock_pack);
+	sigchain_push(SIGPIPE, SIG_IGN);
 	exit_code = do_fetch(gtransport, &rs);
+	sigchain_pop(SIGPIPE);
 	refspec_clear(&rs);
 	transport_disconnect(gtransport);
 	gtransport = NULL;
diff --git a/builtin/fsck.c b/builtin/fsck.c
index bb4227bebc606d..59a96e8c0dd1be 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -49,6 +49,7 @@ static int name_objects;
 #define ERROR_PACK 04
 #define ERROR_REFS 010
 #define ERROR_COMMIT_GRAPH 020
+#define ERROR_MULTI_PACK_INDEX 040
 
 static const char *describe_object(struct object *obj)
 {
@@ -906,7 +907,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 			midx_argv[2] = "--object-dir";
 			midx_argv[3] = odb->path;
 			if (run_command(&midx_verify))
-				errors_found |= ERROR_COMMIT_GRAPH;
+				errors_found |= ERROR_MULTI_PACK_INDEX;
 		}
 	}
 
diff --git a/builtin/gc.c b/builtin/gc.c
index 020f725acc40f4..b170e148bb7e8f 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -27,6 +27,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "gvfs.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -565,6 +566,9 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	if (quiet)
 		argv_array_push(&repack, "-q");
 
+	if ((!auto_gc || (auto_gc && gc_auto_threshold > 0)) && gvfs_config_is_set(GVFS_BLOCK_COMMANDS))
+		die(_("'git gc' is not supported on a GVFS repo"));
+
 	if (auto_gc) {
 		/*
 		 * Auto-gc should be least intrusive as possible.
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index fca70f8e4fcca8..a342e32cf30848 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -3,14 +3,16 @@
 #include "config.h"
 #include "parse-options.h"
 #include "midx.h"
+#include "trace2.h"
 
 static char const * const builtin_multi_pack_index_usage[] = {
-	N_("git multi-pack-index [--object-dir=<dir>] (write|verify)"),
+	N_("git multi-pack-index [--object-dir=<dir>] (write|verify|expire|repack --batch-size=<size>)"),
 	NULL
 };
 
 static struct opts_multi_pack_index {
 	const char *object_dir;
+	unsigned long batch_size;
 } opts;
 
 int cmd_multi_pack_index(int argc, const char **argv,
@@ -19,6 +21,8 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	static struct option builtin_multi_pack_index_options[] = {
 		OPT_FILENAME(0, "object-dir", &opts.object_dir,
 		  N_("object directory containing set of packfile and pack-index pairs")),
+		OPT_MAGNITUDE(0, "batch-size", &opts.batch_size,
+		  N_("during repack, collect pack-files of smaller size into a batch that is larger than this size")),
 		OPT_END(),
 	};
 
@@ -40,10 +44,19 @@ int cmd_multi_pack_index(int argc, const char **argv,
 		return 1;
 	}
 
+	trace2_cmd_mode(argv[0]);
+
+	if (!strcmp(argv[0], "repack"))
+		return midx_repack(opts.object_dir, (size_t)opts.batch_size);
+	if (opts.batch_size)
+		die(_("--batch-size option is only for 'repack' verb"));
+
 	if (!strcmp(argv[0], "write"))
 		return write_midx_file(opts.object_dir);
 	if (!strcmp(argv[0], "verify"))
 		return verify_midx_file(opts.object_dir);
+	if (!strcmp(argv[0], "expire"))
+		return expire_midx_packs(opts.object_dir);
 
 	die(_("unrecognized verb: %s"), argv[0]);
 }
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index a9fac7c128c1eb..a154fc29f6b784 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -33,6 +33,7 @@
 #include "object-store.h"
 #include "dir.h"
 #include "midx.h"
+#include "trace2.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -3473,6 +3474,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	trace2_region_enter("pack-objects", "enumerate-objects",
+			    the_repository);
 	prepare_packing_data(the_repository, &to_pack);
 
 	if (progress)
@@ -3487,12 +3490,23 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (include_tag && nr_result)
 		for_each_ref(add_ref_tag, NULL);
 	stop_progress(&progress_state);
+	trace2_region_leave("pack-objects", "enumerate-objects",
+			    the_repository);
 
 	if (non_empty && !nr_result)
 		return 0;
-	if (nr_result)
+	if (nr_result) {
+		trace2_region_enter("pack-objects", "prepare-pack",
+				    the_repository);
 		prepare_pack(window, depth);
+		trace2_region_leave("pack-objects", "prepare-pack",
+				    the_repository);
+	}
+
+	trace2_region_enter("pack-objects", "write-pack-file", the_repository);
 	write_pack_file();
+	trace2_region_leave("pack-objects", "write-pack-file", the_repository);
+
 	if (progress)
 		fprintf_ln(stderr,
 			   _("Total %"PRIu32" (delta %"PRIu32"),"
diff --git a/builtin/pull.c b/builtin/pull.c
index 701d1473dc59e0..f096d428b94c06 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -122,6 +122,7 @@ static char *opt_update_shallow;
 static char *opt_refmap;
 static char *opt_ipv4;
 static char *opt_ipv6;
+static int opt_show_forced_updates = -1;
 
 static struct option pull_options[] = {
 	/* Shared options */
@@ -233,6 +234,8 @@ static struct option pull_options[] = {
 	OPT_PASSTHRU('6',  "ipv6", &opt_ipv6, NULL,
 		N_("use IPv6 addresses only"),
 		PARSE_OPT_NOARG),
+	OPT_BOOL(0, "show-forced-updates", &opt_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 
 	OPT_END()
 };
@@ -541,6 +544,10 @@ static int run_fetch(const char *repo, const char **refspecs)
 		argv_array_push(&args, opt_ipv4);
 	if (opt_ipv6)
 		argv_array_push(&args, opt_ipv6);
+	if (opt_show_forced_updates > 0)
+		argv_array_push(&args, "--show-forced-updates");
+	else if (opt_show_forced_updates == 0)
+		argv_array_push(&args, "--no-show-forced-updates");
 
 	if (repo) {
 		argv_array_push(&args, repo);
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 7c7bc13e912aa8..40969144b70bca 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1027,6 +1027,14 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		ACTION_EDIT_TODO,
 		ACTION_SHOW_CURRENT_PATCH,
 	} action = NO_ACTION;
+	static const char *action_names[] = { N_("undefined"),
+					      N_("continue"),
+					      N_("skip"),
+					      N_("abort"),
+					      N_("quit"),
+					      N_("edit_todo"),
+					      N_("show_current_patch"),
+					      NULL };
 	const char *gpg_sign = NULL;
 	struct string_list exec = STRING_LIST_INIT_NODUP;
 	const char *rebase_merges = NULL;
@@ -1142,13 +1150,17 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 */
 
 	if (!use_builtin_rebase()) {
-		const char *path = mkpath("%s/git-legacy-rebase",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno(_("could not exec %s"), path);
-		else
-			BUG("sane_execvp() returned???");
+		struct argv_array args = ARGV_ARRAY_INIT;
+		int code;
+
+		argv_array_push(&args, mkpath("%s/git-legacy-rebase",
+					      git_exec_path()));
+		argv_array_pushv(&args, argv + 1);
+		code = run_command_v_opt(args.argv, 0);
+		if (code < 0)
+			die_errno(_("could not exec %s"), args.argv[0]);
+		argv_array_clear(&args);
+		exit(code);
 	}
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
@@ -1212,6 +1224,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		die(_("The --edit-todo action can only be used during "
 		      "interactive rebase."));
 
+	if (trace2_is_enabled()) {
+		if (is_interactive(&options))
+			trace2_cmd_mode("interactive");
+		else if (exec.nr)
+			trace2_cmd_mode("interactive-exec");
+		else
+			trace2_cmd_mode(action_names[action]);
+	}
+
 	switch (action) {
 	case ACTION_CONTINUE: {
 		struct object_id head;
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index d58b7750b6b465..8bc714a5fc30e1 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -694,6 +694,8 @@ static int run_and_feed_hook(const char *hook_name, feed_fn feed,
 	proc.argv = argv;
 	proc.in = -1;
 	proc.stdout_to_stderr = 1;
+	proc.trace2_hook_name = hook_name;
+
 	if (feed_state->push_options) {
 		int i;
 		for (i = 0; i < feed_state->push_options->nr; i++)
@@ -807,6 +809,7 @@ static int run_update_hook(struct command *cmd)
 	proc.stdout_to_stderr = 1;
 	proc.err = use_sideband ? -1 : 0;
 	proc.argv = argv;
+	proc.trace2_hook_name = "update";
 
 	code = start_command(&proc);
 	if (code)
@@ -1190,6 +1193,7 @@ static void run_update_post_hook(struct command *commands)
 	proc.no_stdin = 1;
 	proc.stdout_to_stderr = 1;
 	proc.err = use_sideband ? -1 : 0;
+	proc.trace2_hook_name = "post-update";
 
 	if (!start_command(&proc)) {
 		if (use_sideband)
diff --git a/builtin/repack.c b/builtin/repack.c
index 67f8978043a439..1f9e6fad1bc035 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -129,19 +129,9 @@ static void get_non_kept_pack_filenames(struct string_list *fname_list,
 
 static void remove_redundant_pack(const char *dir_name, const char *base_name)
 {
-	const char *exts[] = {".pack", ".idx", ".keep", ".bitmap", ".promisor"};
-	int i;
 	struct strbuf buf = STRBUF_INIT;
-	size_t plen;
-
-	strbuf_addf(&buf, "%s/%s", dir_name, base_name);
-	plen = buf.len;
-
-	for (i = 0; i < ARRAY_SIZE(exts); i++) {
-		strbuf_setlen(&buf, plen);
-		strbuf_addstr(&buf, exts[i]);
-		unlink(buf.buf);
-	}
+	strbuf_addf(&buf, "%s/%s.pack", dir_name, base_name);
+	unlink_pack_path(buf.buf, 1);
 	strbuf_release(&buf);
 }
 
diff --git a/builtin/reset.c b/builtin/reset.c
index 023fe12be048b2..cc3c9b31367629 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -27,6 +27,7 @@
 #include "submodule-config.h"
 #include "strbuf.h"
 #include "quote.h"
+#include "dir.h"
 
 #define REFRESH_INDEX_DELAY_WARNING_IN_MS (2 * 1000)
 
@@ -99,7 +100,9 @@ static int reset_index(const struct object_id *oid, int reset_type, int quiet)
 
 	if (reset_type == MIXED || reset_type == HARD) {
 		tree = parse_tree_indirect(oid);
+		trace2_region_enter("exp", "prime_cache_tree", the_repository);
 		prime_cache_tree(the_repository, the_repository->index, tree);
+		trace2_region_leave("exp", "prime_cache_tree", the_repository);
 	}
 
 	ret = 0;
@@ -128,12 +131,45 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 		struct diff_options *opt, void *data)
 {
 	int i;
+	int pos;
 	int intent_to_add = *(int *)data;
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filespec *one = q->queue[i]->one;
+		struct diff_filespec *two = q->queue[i]->two;
 		int is_missing = !(one->mode && !is_null_oid(&one->oid));
+		int was_missing = !two->mode && is_null_oid(&two->oid);
 		struct cache_entry *ce;
+		struct cache_entry *ceBefore;
+		struct checkout state = CHECKOUT_INIT;
+
+		/*
+		 * When using the sparse-checkout feature the cache entries that are
+		 * added here will not have the skip-worktree bit set.
+		 * Without this code there is data that is lost because the files that
+		 * would normally be in the working directory are not there and show as
+		 * deleted for the next status or in the case of added files just disappear.
+		 * We need to create the previous version of the files in the working
+		 * directory so that they will have the right content and the next
+		 * status call will show modified or untracked files correctly.
+		 */
+		if (core_apply_sparse_checkout && !file_exists(two->path))
+		{
+			pos = cache_name_pos(two->path, strlen(two->path));
+			if ((pos >= 0 && ce_skip_worktree(active_cache[pos])) && (is_missing || !was_missing))
+			{
+				state.force = 1;
+				state.refresh_cache = 1;
+				state.istate = &the_index;
+				ceBefore = make_cache_entry(&the_index, two->mode, &two->oid, two->path,
+					0, 0);
+				if (!ceBefore)
+					die(_("make_cache_entry failed for path '%s'"),
+						two->path);
+
+				checkout_entry(ceBefore, &state, NULL, NULL);
+			}
+		}
 
 		if (is_missing && !intent_to_add) {
 			remove_file_from_cache(one->path);
@@ -327,7 +363,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 
 	if (read_from_stdin) {
 		strbuf_getline_fn getline_fn = nul_term_line ?
-			strbuf_getline_nul : strbuf_getline_lf;
+			strbuf_getline_nul : strbuf_getline;
 		int flags = PATHSPEC_PREFER_FULL;
 		struct strbuf buf = STRBUF_INIT;
 		struct strbuf unquoted = STRBUF_INIT;
@@ -386,6 +422,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	if (patch_mode) {
 		if (reset_type != NONE)
 			die(_("--patch is incompatible with --{hard,mixed,soft}"));
+		trace2_cmd_mode("patch-interactive");
 		return run_add_interactive(rev, "--patch=reset", &pathspec);
 	}
 
@@ -402,6 +439,11 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	if (reset_type == NONE)
 		reset_type = MIXED; /* by default */
 
+	if (pathspec.nr)
+		trace2_cmd_mode("path");
+	else
+		trace2_cmd_mode(reset_type_names[reset_type]);
+
 	if (reset_type != SOFT && (reset_type != MIXED || get_git_work_tree()))
 		setup_work_tree();
 
@@ -425,6 +467,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			int flags = quiet ? REFRESH_QUIET : REFRESH_IN_PORCELAIN;
 			if (read_from_tree(&pathspec, &oid, intent_to_add))
 				return 1;
+			the_index.updated_skipworktree = 1;
 			if (!quiet && get_git_work_tree()) {
 				uint64_t t_begin, t_delta_in_ms;
 
diff --git a/builtin/stash.c b/builtin/stash.c
index 794fba6e2d5c88..a5ffb10ce6ae25 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -1555,13 +1555,17 @@ int cmd_stash(int argc, const char **argv, const char *prefix)
 	};
 
 	if (!use_builtin_stash()) {
-		const char *path = mkpath("%s/git-legacy-stash",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno(_("could not exec %s"), path);
-		else
-			BUG("sane_execvp() returned???");
+		struct argv_array args = ARGV_ARRAY_INIT;
+		int code;
+
+		argv_array_push(&args, mkpath("%s/git-legacy-stash",
+					      git_exec_path()));
+		argv_array_pushv(&args, argv + 1);
+		code = run_command_v_opt(args.argv, 0);
+		if (code < 0)
+			die_errno(_("could not exec %s"), args.argv[0]);
+		argv_array_clear(&args);
+		exit(code);
 	}
 
 	prefix = setup_git_directory();
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 8937e5cfe41ee8..59448b01602216 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1816,11 +1816,10 @@ static int update_submodules(struct submodule_update_clone *suc)
 {
 	int i;
 
-	run_processes_parallel(suc->max_jobs,
-			       update_clone_get_next_task,
-			       update_clone_start_failure,
-			       update_clone_task_finished,
-			       suc);
+	run_processes_parallel_tr2(suc->max_jobs, update_clone_get_next_task,
+				   update_clone_start_failure,
+				   update_clone_task_finished, suc, "submodule",
+				   "parallel/update");
 
 	/*
 	 * We saved the output and put it out all at once now.
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 02ace602b9ae23..28ea5a4efe5dcc 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -18,6 +18,7 @@
 #include "dir.h"
 #include "split-index.h"
 #include "fsmonitor.h"
+#include "gvfs.h"
 
 /*
  * Default to not allowing changes to the list of files. The
@@ -1070,6 +1071,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	entries = read_cache();
 	if (entries < 0)
 		die("cache corrupted");
+	
+	the_index.updated_skipworktree = 1;
 
 	/*
 	 * Custom copy of parse_options() because we want to handle
@@ -1116,7 +1119,13 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	argc = parse_options_end(&ctx);
 
 	getline_fn = nul_term_line ? strbuf_getline_nul : strbuf_getline_lf;
+	if (mark_skip_worktree_only && gvfs_config_is_set(GVFS_BLOCK_COMMANDS))
+		die(_("modifying the skip worktree bit is not supported on a GVFS repo"));
+	
 	if (preferred_index_format) {
+		if (preferred_index_format != 4 && gvfs_config_is_set(GVFS_BLOCK_COMMANDS))
+			die(_("changing the index version is not supported on a GVFS repo"));
+
 		if (preferred_index_format < INDEX_FORMAT_LB ||
 		    INDEX_FORMAT_UB < preferred_index_format)
 			die("index-version %d not in range: %d..%d",
@@ -1152,6 +1161,9 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	}
 
 	if (split_index > 0) {
+		if (gvfs_config_is_set(GVFS_BLOCK_COMMANDS))
+			die(_("split index is not supported on a GVFS repo"));
+
 		if (git_config_get_split_index() == 0)
 			warning(_("core.splitIndex is set to false; "
 				  "remove or change it, if you really want to "
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 3f9907fcc994d2..6cc094a4538063 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -402,6 +402,7 @@ static int add_worktree(const char *path, const char *refname,
 			cp.dir = path;
 			cp.env = env;
 			cp.argv = NULL;
+			cp.trace2_hook_name = "post-checkout";
 			argv_array_pushl(&cp.args, absolute_path(hook),
 					 oid_to_hex(&null_oid),
 					 oid_to_hex(&commit->object.oid),
diff --git a/cache-tree.c b/cache-tree.c
index 706ffcf1883a01..67c0a1c7f8f519 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -5,6 +5,7 @@
 #include "cache-tree.h"
 #include "object-store.h"
 #include "replace-object.h"
+#include "gvfs.h"
 
 #ifndef DEBUG_CACHE_TREE
 #define DEBUG_CACHE_TREE 0
@@ -243,7 +244,8 @@ static int update_one(struct cache_tree *it,
 		      int flags)
 {
 	struct strbuf buffer;
-	int missing_ok = flags & WRITE_TREE_MISSING_OK;
+	int missing_ok = gvfs_config_is_set(GVFS_MISSING_OK) ?
+		WRITE_TREE_MISSING_OK : (flags & WRITE_TREE_MISSING_OK);
 	int dryrun = flags & WRITE_TREE_DRY_RUN;
 	int repair = flags & WRITE_TREE_REPAIR;
 	int to_invalidate = 0;
@@ -395,7 +397,29 @@ static int update_one(struct cache_tree *it,
 			continue;
 
 		strbuf_grow(&buffer, entlen + 100);
-		strbuf_addf(&buffer, "%o %.*s%c", mode, entlen, path + baselen, '\0');
+
+		switch (mode) {
+		case 0100644:
+			strbuf_add(&buffer, "100644 ", 7);
+			break;
+		case 0100664:
+			strbuf_add(&buffer, "100664 ", 7);
+			break;
+		case 0100755:
+			strbuf_add(&buffer, "100755 ", 7);
+			break;
+		case 0120000:
+			strbuf_add(&buffer, "120000 ", 7);
+			break;
+		case 0160000:
+			strbuf_add(&buffer, "160000 ", 7);
+			break;
+		default:
+			strbuf_addf(&buffer, "%o ", mode);
+			break;
+		}
+		strbuf_add(&buffer, path + baselen, entlen);
+		strbuf_addch(&buffer, '\0');
 		strbuf_add(&buffer, oid->hash, the_hash_algo->rawsz);
 
 #if DEBUG_CACHE_TREE
diff --git a/cache.h b/cache.h
index 877697571c8585..14c2394824608c 100644
--- a/cache.h
+++ b/cache.h
@@ -9,6 +9,7 @@
 #include "gettext.h"
 #include "convert.h"
 #include "trace.h"
+#include "trace2.h"
 #include "string-list.h"
 #include "pack-revindex.h"
 #include "hash.h"
@@ -338,7 +339,9 @@ struct index_state {
 	struct cache_time timestamp;
 	unsigned name_hash_initialized : 1,
 		 initialized : 1,
-		 drop_cache_tree : 1;
+		 drop_cache_tree : 1,
+		 updated_workdir : 1,
+		 updated_skipworktree : 1;
 	struct hashmap name_hash;
 	struct hashmap dir_hash;
 	struct object_id oid;
@@ -886,6 +889,8 @@ extern char *git_replace_ref_base;
 extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
+extern const char *core_virtualfilesystem;
+extern int core_gvfs;
 extern int precomposed_unicode;
 extern int protect_hfs;
 extern int protect_ntfs;
@@ -911,6 +916,8 @@ int use_optional_locks(void);
 extern char comment_line_char;
 extern int auto_comment_line_char;
 
+extern int core_virtualize_objects;
+
 enum log_refs_config {
 	LOG_REFS_UNSET = -1,
 	LOG_REFS_NONE = 0,
diff --git a/commit.c b/commit.c
index a5333c7ac6c373..74b7260e2d85a3 100644
--- a/commit.c
+++ b/commit.c
@@ -590,7 +590,8 @@ void commit_list_sort_by_date(struct commit_list **list)
 }
 
 struct commit *pop_most_recent_commit(struct commit_list **list,
-				      unsigned int mark)
+				      unsigned int mark,
+				      uint32_t min_generation)
 {
 	struct commit *ret = pop_commit(list);
 	struct commit_list *parents = ret->parents;
@@ -599,7 +600,9 @@ struct commit *pop_most_recent_commit(struct commit_list **list,
 		struct commit *commit = parents->item;
 		if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 			commit->object.flags |= mark;
-			commit_list_insert_by_date(commit, list);
+
+			if (commit->generation >= min_generation)
+				commit_list_insert_by_date(commit, list);
 		}
 		parents = parents->next;
 	}
diff --git a/commit.h b/commit.h
index 42728c2906608a..e582020059e051 100644
--- a/commit.h
+++ b/commit.h
@@ -193,9 +193,13 @@ extern const char *skip_blank_lines(const char *msg);
 
 /** Removes the first commit from a list sorted by date, and adds all
  * of its parents.
+ *
+ * The parents are not added if their generation number is strictly
+ * lower than min_generation.
  **/
 struct commit *pop_most_recent_commit(struct commit_list **list,
-				      unsigned int mark);
+				      unsigned int mark,
+				      uint32_t min_generation);
 
 struct commit *pop_commit(struct commit_list **stack);
 
diff --git a/common-main.c b/common-main.c
index 3728f66b4cce80..582a7b18869fb8 100644
--- a/common-main.c
+++ b/common-main.c
@@ -25,22 +25,33 @@ static void restore_sigpipe_to_default(void)
 
 int main(int argc, const char **argv)
 {
+	int result;
+
+	trace2_initialize_clock();
+
 	/*
 	 * Always open file descriptors 0/1/2 to avoid clobbering files
 	 * in die().  It also avoids messing up when the pipes are dup'ed
 	 * onto stdin/stdout/stderr in the child processes we spawn.
 	 */
 	sanitize_stdfds();
+	restore_sigpipe_to_default();
 
 	git_resolve_executable_dir(argv[0]);
 
+	trace2_initialize();
+	trace2_cmd_start(argv);
+	trace2_collect_process_info(TRACE2_PROCESS_INFO_STARTUP);
+
 	git_setup_gettext();
 
 	initialize_the_repository();
 
 	attr_start();
 
-	restore_sigpipe_to_default();
+	result = cmd_main(argc, argv);
+
+	trace2_cmd_exit(result);
 
-	return cmd_main(argc, argv);
+	return result;
 }
diff --git a/compat/mingw.c b/compat/mingw.c
index 3164814fc49d7f..cfa5b17e6a6976 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1959,6 +1959,7 @@ static int try_shell_exec(const char *cmd, char *const *argv)
 		return 0;
 	prog = path_lookup(interpr, 1);
 	if (prog) {
+		int exec_id;
 		int argc = 0;
 #ifndef _MSC_VER
 		const
@@ -1968,13 +1969,16 @@ static int try_shell_exec(const char *cmd, char *const *argv)
 		ALLOC_ARRAY(argv2, argc + 1);
 		argv2[0] = (char *)cmd;	/* full path to the script file */
 		memcpy(&argv2[1], &argv[1], sizeof(*argv) * argc);
+		exec_id = trace2_exec(prog, argv2);
 		pid = mingw_spawnv(prog, argv2, interpr);
 		if (pid >= 0) {
 			int status;
 			if (waitpid(pid, &status, 0) < 0)
 				status = 255;
+			trace2_exec_result(exec_id, status);
 			exit(status);
 		}
+		trace2_exec_result(exec_id, -1);
 		pid = 1;	/* indicate that we tried but failed */
 		free(prog);
 		free(argv2);
@@ -1987,12 +1991,17 @@ int mingw_execv(const char *cmd, char *const *argv)
 	/* check if git_command is a shell script */
 	if (!try_shell_exec(cmd, argv)) {
 		int pid, status;
+		int exec_id;
 
+		exec_id = trace2_exec(cmd, (const char **)argv);
 		pid = mingw_spawnv(cmd, (const char **)argv, NULL);
-		if (pid < 0)
+		if (pid < 0) {
+			trace2_exec_result(exec_id, -1);
 			return -1;
+		}
 		if (waitpid(pid, &status, 0) < 0)
 			status = 255;
+		trace2_exec_result(exec_id, status);
 		exit(status);
 	}
 	return -1;
@@ -3148,6 +3157,8 @@ int wmain(int argc, const wchar_t **wargv)
 
 	SetConsoleCtrlHandler(handle_ctrl_c, TRUE);
 
+	trace2_initialize_clock();
+
 	maybe_redirect_std_handles();
 	adjust_symlink_flags();
 	fsync_object_files = 1;
diff --git a/compat/mingw.h b/compat/mingw.h
index 731bda28363352..46ebd50245aa49 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -146,8 +146,7 @@ static inline int fcntl(int fd, int cmd, ...)
 	errno = EINVAL;
 	return -1;
 }
-/* bash cannot reliably detect negative return codes as failure */
-#define exit(code) exit((code) & 0xff)
+
 #define sigemptyset(x) (void)0
 static inline int sigaddset(sigset_t *set, int signum)
 { return 0; }
diff --git a/compat/poll/poll.c b/compat/poll/poll.c
index b622982b534eea..8050d491b0c5d4 100644
--- a/compat/poll/poll.c
+++ b/compat/poll/poll.c
@@ -149,7 +149,7 @@ win32_compute_revents (HANDLE h, int *p_sought)
     case FILE_TYPE_PIPE:
       if (!once_only)
 	{
-	  NtQueryInformationFile = (PNtQueryInformationFile)
+	  NtQueryInformationFile = (PNtQueryInformationFile)(void (*)(void))
 	    GetProcAddress (GetModuleHandleA ("ntdll.dll"),
 			    "NtQueryInformationFile");
 	  once_only = TRUE;
diff --git a/compat/win32/exit-process.h b/compat/win32/exit-process.h
index 88e3bbc83c499e..d53989884cfb0c 100644
--- a/compat/win32/exit-process.h
+++ b/compat/win32/exit-process.h
@@ -130,7 +130,8 @@ static int exit_process(HANDLE process, int exit_code)
 			HINSTANCE kernel32 = GetModuleHandleA("kernel32");
 			if (!kernel32)
 				die("BUG: cannot find kernel32");
-			exit_process_address = (LPTHREAD_START_ROUTINE)
+			exit_process_address =
+				(LPTHREAD_START_ROUTINE)(void (*)(void))
 				GetProcAddress(kernel32, "ExitProcess");
 			initialized = 1;
 		}
diff --git a/compat/win32/trace2_win32_process_info.c b/compat/win32/trace2_win32_process_info.c
new file mode 100644
index 00000000000000..8ccbd1c2c6f82d
--- /dev/null
+++ b/compat/win32/trace2_win32_process_info.c
@@ -0,0 +1,191 @@
+#include "../../cache.h"
+#include "../../json-writer.h"
+#include "lazyload.h"
+#include <Psapi.h>
+#include <tlHelp32.h>
+
+/*
+ * An arbitrarily chosen value to limit the size of the ancestor
+ * array built in git_processes().
+ */
+#define NR_PIDS_LIMIT 10
+
+/*
+ * Find the process data for the given PID in the given snapshot
+ * and update the PROCESSENTRY32 data.
+ */
+static int find_pid(DWORD pid, HANDLE hSnapshot, PROCESSENTRY32 *pe32)
+{
+	pe32->dwSize = sizeof(PROCESSENTRY32);
+
+	if (Process32First(hSnapshot, pe32)) {
+		do {
+			if (pe32->th32ProcessID == pid)
+				return 1;
+		} while (Process32Next(hSnapshot, pe32));
+	}
+	return 0;
+}
+
+/*
+ * Accumulate JSON array of our parent processes:
+ *     [
+ *         exe-name-parent,
+ *         exe-name-grand-parent,
+ *         ...
+ *     ]
+ *
+ * Note: we only report the filename of the process executable; the
+ *       only way to get its full pathname is to use OpenProcess()
+ *       and GetModuleFileNameEx() or QueryfullProcessImageName()
+ *       and that seems rather expensive (on top of the cost of
+ *       getting the snapshot).
+ *
+ * Note: we compute the set of parent processes by walking the PPID
+ *       link in each visited PROCESSENTRY32 record.  This search
+ *       stops when an ancestor process is not found in the snapshot
+ *       (because it exited before the current or intermediate parent
+ *       process exited).
+ *
+ *       This search may compute an incorrect result if the PPID link
+ *       refers to the PID of an exited parent and that PID has been
+ *       recycled and given to a new unrelated process.
+ *
+ *       Worse, it is possible for a child or descendant of the
+ *       current process to be given the recycled PID and cause a
+ *       PPID-cycle.  This would cause an infinite loop building our
+ *       parent process array.
+ *
+ * Note: for completeness, the "System Idle" process has PID=0 and
+ *       PPID=0 and could cause another PPID-cycle.  We don't expect
+ *       Git to be a descendant of the idle process, but because of
+ *       PID recycling, it might be possible to get a PPID link value
+ *       of 0.  This too would cause an infinite loop.
+ *
+ * Therefore, we keep an array of the visited PPIDs to guard against
+ * cycles.
+ *
+ * We use a fixed-size array rather than ALLOC_GROW to keep things
+ * simple and avoid the alloc/realloc overhead.  It is OK if we
+ * truncate the search and return a partial answer.
+ */
+static void get_processes(struct json_writer *jw, HANDLE hSnapshot)
+{
+	PROCESSENTRY32 pe32;
+	DWORD pid;
+	DWORD pid_list[NR_PIDS_LIMIT];
+	int k, nr_pids = 0;
+
+	pid = GetCurrentProcessId();
+	while (find_pid(pid, hSnapshot, &pe32)) {
+		/* Only report parents. Omit self from the JSON output. */
+		if (nr_pids)
+			jw_array_string(jw, pe32.szExeFile);
+
+		/* Check for cycle in snapshot. (Yes, it happened.) */
+		for (k = 0; k < nr_pids; k++)
+			if (pid == pid_list[k]) {
+				jw_array_string(jw, "(cycle)");
+				return;
+			}
+
+		if (nr_pids == NR_PIDS_LIMIT) {
+			jw_array_string(jw, "(truncated)");
+			return;
+		}
+
+		pid_list[nr_pids++] = pid;
+
+		pid = pe32.th32ParentProcessID;
+	}
+}
+
+/*
+ * Emit JSON data for the current and parent processes.  Individual
+ * trace2 targets can decide how to actually print it.
+ */
+static void get_ancestry(void)
+{
+	HANDLE hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+
+	if (hSnapshot != INVALID_HANDLE_VALUE) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_array_begin(&jw, 0);
+		get_processes(&jw, hSnapshot);
+		jw_end(&jw);
+
+		trace2_data_json("process", the_repository, "windows/ancestry",
+				 &jw);
+
+		jw_release(&jw);
+		CloseHandle(hSnapshot);
+	}
+}
+
+/*
+ * Is a debugger attached to the current process?
+ *
+ * This will catch debug runs (where the debugger started the process).
+ * This is the normal case.  Since this code is called during our startup,
+ * it will not report instances where a debugger is attached dynamically
+ * to a running git process, but that is relatively rare.
+ */
+static void get_is_being_debugged(void)
+{
+	if (IsDebuggerPresent())
+		trace2_data_intmax("process", the_repository,
+				   "windows/debugger_present", 1);
+}
+
+/*
+ * Emit JSON data with the peak memory usage of the current process.
+ */
+static void get_peak_memory_info(void)
+{
+	DECLARE_PROC_ADDR(psapi.dll, BOOL, GetProcessMemoryInfo, HANDLE,
+			  PPROCESS_MEMORY_COUNTERS, DWORD);
+
+	if (INIT_PROC_ADDR(GetProcessMemoryInfo)) {
+		PROCESS_MEMORY_COUNTERS pmc;
+
+		if (GetProcessMemoryInfo(GetCurrentProcess(), &pmc,
+					 sizeof(pmc))) {
+			struct json_writer jw = JSON_WRITER_INIT;
+
+			jw_object_begin(&jw, 0);
+
+#define KV(kv) #kv, (intmax_t)pmc.kv
+
+			jw_object_intmax(&jw, KV(PageFaultCount));
+			jw_object_intmax(&jw, KV(PeakWorkingSetSize));
+			jw_object_intmax(&jw, KV(PeakPagefileUsage));
+
+			jw_end(&jw);
+
+			trace2_data_json("process", the_repository,
+					 "windows/memory", &jw);
+			jw_release(&jw);
+		}
+	}
+}
+
+void trace2_collect_process_info(enum trace2_process_info_reason reason)
+{
+	if (!trace2_is_enabled())
+		return;
+
+	switch (reason) {
+	case TRACE2_PROCESS_INFO_STARTUP:
+		get_is_being_debugged();
+		get_ancestry();
+		return;
+
+	case TRACE2_PROCESS_INFO_EXIT:
+		get_peak_memory_info();
+		return;
+
+	default:
+		BUG("trace2_collect_process_info: unknown reason '%d'", reason);
+	}
+}
diff --git a/config.c b/config.c
index 279b9e8b187d9f..29f3b547acfc91 100644
--- a/config.c
+++ b/config.c
@@ -19,6 +19,7 @@
 #include "utf8.h"
 #include "dir.h"
 #include "color.h"
+#include "gvfs.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -1324,8 +1325,17 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.gvfs")) {
+		gvfs_load_config_value(value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.sparsecheckout")) {
-		core_apply_sparse_checkout = git_config_bool(var, value);
+		/* virtual file system relies on the sparse checkout logic so force it on */
+		if (core_virtualfilesystem)
+			core_apply_sparse_checkout = 1;
+		else
+			core_apply_sparse_checkout = git_config_bool(var, value);
 		return 0;
 	}
 
@@ -1354,6 +1364,11 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.virtualizeobjects")) {
+		core_virtualize_objects = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return platform_core_config(var, value, cb);
 }
@@ -1693,14 +1708,15 @@ static int do_git_config_sequence(const struct config_options *opts,
 		ret += git_config_from_file(fn, user_config, data);
 
 	current_parsing_scope = CONFIG_SCOPE_REPO;
-	if (repo_config && !access_or_die(repo_config, R_OK, 0))
+	if (!opts->ignore_repo && repo_config &&
+	    !access_or_die(repo_config, R_OK, 0))
 		ret += git_config_from_file(fn, repo_config, data);
 
 	/*
 	 * Note: this should have a new scope, CONFIG_SCOPE_WORKTREE.
 	 * But let's not complicate things before it's actually needed.
 	 */
-	if (repository_format_worktree_config) {
+	if (!opts->ignore_worktree && repository_format_worktree_config) {
 		char *path = git_pathdup("config.worktree");
 		if (!access_or_die(path, R_OK, 0))
 			ret += git_config_from_file(fn, path, data);
@@ -1708,7 +1724,7 @@ static int do_git_config_sequence(const struct config_options *opts,
 	}
 
 	current_parsing_scope = CONFIG_SCOPE_CMDLINE;
-	if (git_config_from_parameters(fn, data) < 0)
+	if (!opts->ignore_cmdline && git_config_from_parameters(fn, data) < 0)
 		die(_("unable to parse command-line config"));
 
 	current_parsing_scope = CONFIG_SCOPE_UNKNOWN;
@@ -1799,6 +1815,22 @@ void read_early_config(config_fn_t cb, void *data)
 	strbuf_release(&gitdir);
 }
 
+/*
+ * Read config but only enumerate system and global settings.
+ * Omit any repo-local, worktree-local, or command-line settings.
+ */
+void read_very_early_config(config_fn_t cb, void *data)
+{
+	struct config_options opts = { 0 };
+
+	opts.respect_includes = 1;
+	opts.ignore_repo = 1;
+	opts.ignore_worktree = 1;
+	opts.ignore_cmdline = 1;
+
+	config_with_options(cb, data, NULL, &opts);
+}
+
 static struct config_set_element *configset_find_element(struct config_set *cs, const char *key)
 {
 	struct config_set_element k;
@@ -2016,7 +2048,7 @@ int git_configset_get_pathname(struct config_set *cs, const char *key, const cha
 /* Functions use to read configuration from a repository */
 static void repo_read_config(struct repository *repo)
 {
-	struct config_options opts;
+	struct config_options opts = { 0 };
 
 	opts.respect_includes = 1;
 	opts.commondir = repo->commondir;
@@ -2301,6 +2333,37 @@ int git_config_get_fsmonitor(void)
 	return 0;
 }
 
+int git_config_get_virtualfilesystem(void)
+{
+	if (git_config_get_pathname("core.virtualfilesystem", &core_virtualfilesystem))
+		core_virtualfilesystem = getenv("GIT_VIRTUALFILESYSTEM_TEST");
+
+	if (core_virtualfilesystem && !*core_virtualfilesystem)
+		core_virtualfilesystem = NULL;
+
+	if (core_virtualfilesystem) {
+		/*
+		 * Some git commands spawn helpers and redirect the index to a different
+		 * location.  These include "difftool -d" and the sequencer
+		 * (i.e. `git rebase -i`, `git cherry-pick` and `git revert`) and others.
+		 * In those instances we don't want to update their temporary index with
+		 * our virtualization data.
+		 */
+		char *default_index_file = xstrfmt("%s/%s", the_repository->gitdir, "index");
+		int should_run_hook = !strcmp(default_index_file, the_repository->index_file);
+
+		free(default_index_file);
+		if (should_run_hook) {
+			/* virtual file system relies on the sparse checkout logic so force it on */
+			core_apply_sparse_checkout = 1;
+			return 1;
+		} 
+		core_virtualfilesystem = NULL;
+	}
+
+	return 0;
+}
+
 int git_config_get_index_threads(int *dest)
 {
 	int is_bool, val;
@@ -2662,6 +2725,8 @@ int git_config_set_gently(const char *key, const char *value)
 void git_config_set(const char *key, const char *value)
 {
 	git_config_set_multivar(key, value, NULL, 0);
+
+	trace2_cmd_set_config(key, value);
 }
 
 /*
diff --git a/config.h b/config.h
index ee5d3fa7b4264f..d706db8067e2b7 100644
--- a/config.h
+++ b/config.h
@@ -55,6 +55,9 @@ typedef int (*config_parser_event_fn_t)(enum config_event_t type,
 
 struct config_options {
 	unsigned int respect_includes : 1;
+	unsigned int ignore_repo : 1;
+	unsigned int ignore_worktree : 1;
+	unsigned int ignore_cmdline : 1;
 	const char *commondir;
 	const char *git_dir;
 	config_parser_event_fn_t event_fn;
@@ -83,6 +86,7 @@ extern int git_config_from_blob_oid(config_fn_t fn, const char *name,
 extern void git_config_push_parameter(const char *text);
 extern int git_config_from_parameters(config_fn_t fn, void *data);
 extern void read_early_config(config_fn_t cb, void *data);
+extern void read_very_early_config(config_fn_t cb, void *data);
 extern void git_config(config_fn_t fn, void *);
 extern int config_with_options(config_fn_t fn, void *,
 			       struct git_config_source *config_source,
@@ -251,6 +255,7 @@ extern int git_config_get_untracked_cache(void);
 extern int git_config_get_split_index(void);
 extern int git_config_get_max_percent_split_change(void);
 extern int git_config_get_fsmonitor(void);
+extern int git_config_get_virtualfilesystem(void);
 
 /* This dies if the configured or default date is in the future */
 extern int git_config_get_expiry(const char *key, const char **output);
diff --git a/config.mak.uname b/config.mak.uname
index 32381f5fd102fb..77834c2f9bf37c 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -133,6 +133,8 @@ ifeq ($(uname_S),Darwin)
 	HAVE_BSD_SYSCTL = YesPlease
 	FREAD_READS_DIRECTORIES = UnfortunatelyYes
 	HAVE_NS_GET_EXECUTABLE_PATH = YesPlease
+	BASIC_CFLAGS += -I/usr/local/include
+	BASIC_LDFLAGS += -L/usr/local/lib
 endif
 ifeq ($(uname_S),SunOS)
 	NEEDS_SOCKET = YesPlease
@@ -426,7 +428,9 @@ ifeq ($(uname_S),Windows)
 	CFLAGS =
 	BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
 	COMPAT_OBJS = compat/msvc.o compat/winansi.o \
+		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
+		compat/win32/trace2_win32_process_info.o \
 		compat/win32/dirent.o compat/win32/fscache.o
 	COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DDETECT_MSYS_TTY -DNOGDI -DHAVE_STRING_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
 	BASIC_LDFLAGS = -IGNORE:4217 -IGNORE:4049 -NOLOGO -ENTRY:wmainCRTStartup -SUBSYSTEM:CONSOLE
@@ -604,6 +608,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	COMPAT_CFLAGS += -DNOGDI -Icompat -Icompat/win32
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
 	COMPAT_OBJS += compat/mingw.o compat/winansi.o \
+		compat/win32/trace2_win32_process_info.o \
 		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
 		compat/win32/dirent.o compat/win32/fscache.o
@@ -625,7 +630,7 @@ ifneq (,$(wildcard ../THIS_IS_MSYSGIT))
 	NO_GETTEXT = YesPlease
 	COMPAT_CLFAGS += -D__USE_MINGW_ACCESS
 else
-	ifeq ($(shell expr "$(uname_R)" : '2\.'),2)
+	ifneq ($(shell expr "$(uname_R)" : '1\.'),2)
 		# MSys2
 		prefix = /usr/
 		# Enable DEP
diff --git a/connect.c b/connect.c
index e937b8ca0490be..da7daa2b683f9a 100644
--- a/connect.c
+++ b/connect.c
@@ -1252,6 +1252,7 @@ struct child_process *git_connect(int fd[2], const char *url,
 		conn = NULL;
 	} else if (protocol == PROTO_GIT) {
 		conn = git_connect_git(fd, hostandport, path, prog, version, flags);
+		conn->trace2_child_class = "transport/git";
 	} else {
 		struct strbuf cmd = STRBUF_INIT;
 		const char *const *var;
@@ -1294,9 +1295,11 @@ struct child_process *git_connect(int fd[2], const char *url,
 				strbuf_release(&cmd);
 				return NULL;
 			}
+			conn->trace2_child_class = "transport/ssh";
 			fill_ssh_args(conn, ssh_host, port, version, flags);
 		} else {
 			transport_check_allowed("file");
+			conn->trace2_child_class = "transport/file";
 			if (version > 0) {
 				argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
 						 version);
diff --git a/connected.c b/connected.c
index 1bba888eff90a2..078ec309572b4e 100644
--- a/connected.c
+++ b/connected.c
@@ -4,6 +4,7 @@
 #include "connected.h"
 #include "transport.h"
 #include "packfile.h"
+#include "gvfs.h"
 
 /*
  * If we feed all the commits we want to verify to this command
@@ -28,6 +29,26 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 	struct transport *transport;
 	size_t base_len;
 
+	/*
+	 * Running a virtual file system there will be objects that are
+	 * missing locally and we don't want to download a bunch of
+	 * commits, trees, and blobs just to make sure everything is
+	 * reachable locally so this option will skip reachablility
+	 * checks below that use rev-list.  This will stop the check
+	 * before uploadpack runs to determine if there is anything to
+	 * fetch.  Returning zero for the first check will also prevent the
+	 * uploadpack from happening.  It will also skip the check after
+	 * the fetch is finished to make sure all the objects where
+	 * downloaded in the pack file.  This will allow the fetch to
+	 * run and get all the latest tip commit ids for all the branches
+	 * in the fetch but not pull down commits, trees, or blobs via
+	 * upload pack.
+	 */
+	if (gvfs_config_is_set(GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK))
+		return 0;
+	if (core_virtualize_objects)
+		return 0;
+
 	if (!opt)
 		opt = &defaults;
 	transport = opt->transport;
diff --git a/contrib/long-running-read-object/example.pl b/contrib/long-running-read-object/example.pl
new file mode 100644
index 00000000000000..b8f37f836a813c
--- /dev/null
+++ b/contrib/long-running-read-object/example.pl
@@ -0,0 +1,114 @@
+#!/usr/bin/perl
+#
+# Example implementation for the Git read-object protocol version 1
+# See Documentation/technical/read-object-protocol.txt
+#
+# Allows you to test the ability for blobs to be pulled from a host git repo
+# "on demand."  Called when git needs a blob it couldn't find locally due to
+# a lazy clone that only cloned the commits and trees.
+#
+# A lazy clone can be simulated via the following commands from the host repo
+# you wish to create a lazy clone of:
+#
+# cd /host_repo
+# git rev-parse HEAD
+# git init /guest_repo
+# git cat-file --batch-check --batch-all-objects | grep -v 'blob' |
+#	cut -d' ' -f1 | git pack-objects /guest_repo/.git/objects/pack/noblobs
+# cd /guest_repo
+# git config core.virtualizeobjects true
+# git reset --hard <sha from rev-parse call above>
+#
+# Please note, this sample is a minimal skeleton. No proper error handling
+# was implemented.
+#
+
+use strict;
+use warnings;
+
+#
+# Point $DIR to the folder where your host git repo is located so we can pull
+# missing objects from it
+#
+my $DIR = "/host_repo/.git/";
+
+sub packet_bin_read {
+	my $buffer;
+	my $bytes_read = read STDIN, $buffer, 4;
+	if ( $bytes_read == 0 ) {
+
+		# EOF - Git stopped talking to us!
+		exit();
+	}
+	elsif ( $bytes_read != 4 ) {
+		die "invalid packet: '$buffer'";
+	}
+	my $pkt_size = hex($buffer);
+	if ( $pkt_size == 0 ) {
+		return ( 1, "" );
+	}
+	elsif ( $pkt_size > 4 ) {
+		my $content_size = $pkt_size - 4;
+		$bytes_read = read STDIN, $buffer, $content_size;
+		if ( $bytes_read != $content_size ) {
+			die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
+		}
+		return ( 0, $buffer );
+	}
+	else {
+		die "invalid packet size: $pkt_size";
+	}
+}
+
+sub packet_txt_read {
+	my ( $res, $buf ) = packet_bin_read();
+	unless ( $buf =~ s/\n$// ) {
+		die "A non-binary line MUST be terminated by an LF.";
+	}
+	return ( $res, $buf );
+}
+
+sub packet_bin_write {
+	my $buf = shift;
+	print STDOUT sprintf( "%04x", length($buf) + 4 );
+	print STDOUT $buf;
+	STDOUT->flush();
+}
+
+sub packet_txt_write {
+	packet_bin_write( $_[0] . "\n" );
+}
+
+sub packet_flush {
+	print STDOUT sprintf( "%04x", 0 );
+	STDOUT->flush();
+}
+
+( packet_txt_read() eq ( 0, "git-read-object-client" ) ) || die "bad initialize";
+( packet_txt_read() eq ( 0, "version=1" ) )				 || die "bad version";
+( packet_bin_read() eq ( 1, "" ) )                       || die "bad version end";
+
+packet_txt_write("git-read-object-server");
+packet_txt_write("version=1");
+packet_flush();
+
+( packet_txt_read() eq ( 0, "capability=get" ) )    || die "bad capability";
+( packet_bin_read() eq ( 1, "" ) )                  || die "bad capability end";
+
+packet_txt_write("capability=get");
+packet_flush();
+
+while (1) {
+	my ($command) = packet_txt_read() =~ /^command=([^=]+)$/;
+
+	if ( $command eq "get" ) {
+		my ($sha1) = packet_txt_read() =~ /^sha1=([0-9a-f]{40})$/;
+		packet_bin_read();
+
+		system ('git --git-dir="' . $DIR . '" cat-file blob ' . $sha1 . ' | git -c core.virtualizeobjects=false hash-object -w --stdin >/dev/null 2>&1');
+		packet_txt_write(($?) ? "status=error" : "status=success");
+		packet_flush();
+	} else {
+		die "bad command '$command'";
+	}
+}
diff --git a/convert.c b/convert.c
index 5d0307fc1004f2..f799d8e167d52e 100644
--- a/convert.c
+++ b/convert.c
@@ -8,6 +8,7 @@
 #include "pkt-line.h"
 #include "sub-process.h"
 #include "utf8.h"
+#include "gvfs.h"
 
 /*
  * convert.c - convert a file when checking it out and checking it in.
@@ -564,6 +565,9 @@ static int crlf_to_git(const struct index_state *istate,
 	if (!buf)
 		return 1;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("CRLF conversions not supported when running under GVFS");
+
 	/* only grow if not in place */
 	if (strbuf_avail(buf) + buf->len < len)
 		strbuf_grow(buf, len - buf->len);
@@ -603,6 +607,9 @@ static int crlf_to_worktree(const char *src, size_t len,
 	if (!will_convert_lf_to_crlf(&stats, crlf_action))
 		return 0;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("CRLF conversions not supported when running under GVFS");
+
 	/* are we "faking" in place editing ? */
 	if (src == buf->buf)
 		to_free = strbuf_detach(buf, NULL);
@@ -717,6 +724,9 @@ static int apply_single_file_filter(const char *path, const char *src, size_t le
 	struct async async;
 	struct filter_params params;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("Filter \"%s\" not supported when running under GVFS", cmd);
+
 	memset(&async, 0, sizeof(async));
 	async.proc = filter_buffer_or_fd;
 	async.data = &params;
@@ -1101,6 +1111,9 @@ static int ident_to_git(const char *src, size_t len,
 	if (!buf)
 		return 1;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("ident conversions not supported when running under GVFS");
+
 	/* only grow if not in place */
 	if (strbuf_avail(buf) + buf->len < len)
 		strbuf_grow(buf, len - buf->len);
@@ -1148,6 +1161,9 @@ static int ident_to_worktree(const char *src, size_t len,
 	if (!cnt)
 		return 0;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("ident conversions not supported when running under GVFS");
+
 	/* are we "faking" in place editing ? */
 	if (src == buf->buf)
 		to_free = strbuf_detach(buf, NULL);
@@ -1580,6 +1596,9 @@ static int lf_to_crlf_filter_fn(struct stream_filter *filter,
 	size_t count, o = 0;
 	struct lf_to_crlf_filter *lf_to_crlf = (struct lf_to_crlf_filter *)filter;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("CRLF conversions not supported when running under GVFS");
+
 	/*
 	 * We may be holding onto the CR to see if it is followed by a
 	 * LF, in which case we would need to go to the main loop.
@@ -1824,6 +1843,9 @@ static int ident_filter_fn(struct stream_filter *filter,
 	struct ident_filter *ident = (struct ident_filter *)filter;
 	static const char head[] = "$Id";
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("ident conversions not supported when running under GVFS");
+
 	if (!input) {
 		/* drain upon eof */
 		switch (ident->state) {
diff --git a/dir.c b/dir.c
index a0169511344883..7f8ef267664cec 100644
--- a/dir.c
+++ b/dir.c
@@ -20,6 +20,7 @@
 #include "ewah/ewok.h"
 #include "fsmonitor.h"
 #include "submodule-config.h"
+#include "virtualfilesystem.h"
 
 /*
  * Tells read_directory_recursive how a file or directory should be treated.
@@ -1121,6 +1122,18 @@ int is_excluded_from_list(const char *pathname,
 			  struct exclude_list *el, struct index_state *istate)
 {
 	struct exclude *exclude;
+
+	/*
+	 * The virtual file system data is used to prevent git from traversing
+	 * any part of the tree that is not in the virtual file system.  Return
+	 * 1 to exclude the entry if it is not found in the virtual file system,
+	 * else fall through to the regular excludes logic as it may further exclude.
+	 */
+	if (*dtype == DT_UNKNOWN)
+		*dtype = get_dtype(NULL, istate, pathname, pathlen);
+	if (is_excluded_from_virtualfilesystem(pathname, pathlen, *dtype) > 0)
+		return 1;
+
 	exclude = last_exclude_matching_from_list(pathname, pathlen, basename,
 						  dtype, el, istate);
 	if (exclude)
@@ -1336,8 +1349,20 @@ struct exclude *last_exclude_matching(struct dir_struct *dir,
 int is_excluded(struct dir_struct *dir, struct index_state *istate,
 		const char *pathname, int *dtype_p)
 {
-	struct exclude *exclude =
-		last_exclude_matching(dir, istate, pathname, dtype_p);
+	struct exclude *exclude;
+
+	/*
+	 * The virtual file system data is used to prevent git from traversing
+	 * any part of the tree that is not in the virtual file system.  Return
+	 * 1 to exclude the entry if it is not found in the virtual file system,
+	 * else fall through to the regular excludes logic as it may further exclude.
+	 */
+	if (*dtype_p == DT_UNKNOWN)
+		*dtype_p = get_dtype(NULL, istate, pathname, strlen(pathname));
+	if (is_excluded_from_virtualfilesystem(pathname, strlen(pathname), *dtype_p) > 0)
+		return 1;
+
+	exclude = last_exclude_matching(dir, istate, pathname, dtype_p);
 	if (exclude)
 		return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
 	return 0;
@@ -1690,6 +1715,9 @@ static enum path_treatment treat_one_path(struct dir_struct *dir,
 	if (dtype != DT_DIR && has_path_in_index)
 		return path_none;
 
+	if (is_excluded_from_virtualfilesystem(path->buf, path->len, dtype) > 0)
+		return path_excluded;
+
 	/*
 	 * When we are looking at a directory P in the working tree,
 	 * there are three cases:
@@ -2030,6 +2058,8 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 		/* add the path to the appropriate result list */
 		switch (state) {
 		case path_excluded:
+			if (is_excluded_from_virtualfilesystem(path.buf, path.len, DT_DIR) > 0)
+				break;
 			if (dir->flags & DIR_SHOW_IGNORED)
 				dir_add_name(dir, istate, path.buf, path.len);
 			else if ((dir->flags & DIR_SHOW_IGNORED_TOO) ||
diff --git a/editor.c b/editor.c
index c985eee1f9d1c7..71547674ab4e88 100644
--- a/editor.c
+++ b/editor.c
@@ -78,6 +78,7 @@ static int launch_specified_editor(const char *editor, const char *path,
 		p.argv = args;
 		p.env = env;
 		p.use_shell = 1;
+		p.trace2_child_class = "editor";
 		if (start_command(&p) < 0)
 			return error("unable to start editor '%s'", editor);
 
diff --git a/environment.c b/environment.c
index 89af47cb850490..23ca0ffdcf5e8c 100644
--- a/environment.c
+++ b/environment.c
@@ -69,9 +69,12 @@ enum object_creation_mode object_creation_mode = OBJECT_CREATION_MODE;
 char *notes_ref_name;
 int grafts_replace_parents = 1;
 int core_apply_sparse_checkout;
+int core_gvfs;
+const char *core_virtualfilesystem;
 int merge_log_config = -1;
 int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 unsigned long pack_size_limit_cfg;
+int core_virtualize_objects;
 enum log_refs_config log_all_ref_updates = LOG_REFS_UNSET;
 
 #ifndef PROTECT_HFS_DEFAULT
diff --git a/exec-cmd.c b/exec-cmd.c
index 4f81f443105f07..7deeab30397cf2 100644
--- a/exec-cmd.c
+++ b/exec-cmd.c
@@ -209,6 +209,8 @@ static int git_get_exec_path(struct strbuf *buf, const char *argv0)
 		return -1;
 	}
 
+	trace2_cmd_path(buf->buf);
+
 	return 0;
 }
 
diff --git a/fetch-pack.c b/fetch-pack.c
index 9e65a240ac3e5d..fc4a2b26c52527 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -191,8 +191,10 @@ static void send_request(struct fetch_pack_args *args,
 	if (args->stateless_rpc) {
 		send_sideband(fd, -1, buf->buf, buf->len, LARGE_PACKET_MAX);
 		packet_flush(fd);
-	} else
-		write_or_die(fd, buf->buf, buf->len);
+	} else {
+		if (write_in_full(fd, buf->buf, buf->len) < 0)
+			die_errno(_("unable to write to remote"));
+	}
 }
 
 static void insert_one_alternate_object(struct fetch_negotiator *negotiator,
@@ -532,7 +534,8 @@ static void mark_recent_complete_commits(struct fetch_pack_args *args,
 	while (complete && cutoff <= complete->item->date) {
 		print_verbose(args, _("Marking %s as complete"),
 			      oid_to_hex(&complete->item->object.oid));
-		pop_most_recent_commit(&complete, COMPLETE);
+		pop_most_recent_commit(&complete, COMPLETE,
+				       GENERATION_NUMBER_ZERO);
 	}
 }
 
@@ -1165,7 +1168,8 @@ static int send_fetch_request(struct fetch_negotiator *negotiator, int fd_out,
 
 	/* Send request */
 	packet_buf_flush(&req_buf);
-	write_or_die(fd_out, req_buf.buf, req_buf.len);
+	if (write_in_full(fd_out, req_buf.buf, req_buf.len) < 0)
+		die_errno(_("unable to write request to remote"));
 
 	strbuf_release(&req_buf);
 	return ret;
diff --git a/git-compat-util.h b/git-compat-util.h
index e0275da7e0a794..4ad9137d6a8013 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -210,6 +210,7 @@
 #include "compat/mingw.h"
 #include "compat/win32/fscache.h"
 #elif defined(_MSC_VER)
+#include "compat/win32/path-utils.h"
 #include "compat/msvc.h"
 #include "compat/win32/fscache.h"
 #else
@@ -1322,6 +1323,13 @@ struct fscache;
 
 extern int cmd_main(int, const char **);
 
+/*
+ * Intercept all calls to exit() and route them to trace2 to
+ * optionally emit a message before calling the real exit().
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+#define exit(code) exit(trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
 /*
  * You can mark a stack variable with UNLEAK(var) to avoid it being
  * reported as a leak by tools like LSAN or valgrind. The argument
diff --git a/git.c b/git.c
index c2330275b38cc4..71e6a334c265c2 100644
--- a/git.c
+++ b/git.c
@@ -4,6 +4,8 @@
 #include "help.h"
 #include "run-command.h"
 #include "alias.h"
+#include "dir.h"
+#include "gvfs.h"
 
 #define RUN_SETUP		(1<<0)
 #define RUN_SETUP_GENTLY	(1<<1)
@@ -16,6 +18,7 @@
 #define SUPPORT_SUPER_PREFIX	(1<<4)
 #define DELAY_PAGER_CONFIG	(1<<5)
 #define NO_PARSEOPT		(1<<6) /* parse-options is not used */
+#define BLOCK_ON_GVFS_REPO	(1<<7) /* command not allowed in GVFS repos */
 
 struct cmd_struct {
 	const char *cmd;
@@ -147,16 +150,20 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				git_set_exec_path(cmd + 1);
 			else {
 				puts(git_exec_path());
+				trace2_cmd_name("_query_");
 				exit(0);
 			}
 		} else if (!strcmp(cmd, "--html-path")) {
 			puts(system_path(GIT_HTML_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--man-path")) {
 			puts(system_path(GIT_MAN_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--info-path")) {
 			puts(system_path(GIT_INFO_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "-p") || !strcmp(cmd, "--paginate")) {
 			use_pager = 1;
@@ -285,6 +292,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			(*argv)++;
 			(*argc)--;
 		} else if (skip_prefix(cmd, "--list-cmds=", &cmd)) {
+			trace2_cmd_name("_query_");
 			if (!strcmp(cmd, "parseopt")) {
 				struct string_list list = STRING_LIST_INIT_DUP;
 				int i;
@@ -332,9 +340,14 @@ static int handle_alias(int *argcp, const char ***argv)
 			commit_pager_choice();
 
 			child.use_shell = 1;
+			child.trace2_child_class = "shell_alias";
 			argv_array_push(&child.args, alias_string + 1);
 			argv_array_pushv(&child.args, (*argv) + 1);
 
+			trace2_cmd_alias(alias_command, child.args.argv);
+			trace2_cmd_list_config();
+			trace2_cmd_name("_run_shell_alias_");
+
 			ret = run_command(&child);
 			if (ret >= 0)   /* normal exit */
 				exit(ret);
@@ -369,6 +382,9 @@ static int handle_alias(int *argcp, const char ***argv)
 		/* insert after command name */
 		memcpy(new_argv + count, *argv + 1, sizeof(char *) * *argcp);
 
+		trace2_cmd_alias(alias_command, new_argv);
+		trace2_cmd_list_config();
+
 		*argv = new_argv;
 		*argcp += count - 1;
 
@@ -380,6 +396,64 @@ static int handle_alias(int *argcp, const char ***argv)
 	return ret;
 }
 
+/* Runs pre/post-command hook */
+static struct argv_array sargv = ARGV_ARRAY_INIT;
+static int run_post_hook = 0;
+static int exit_code = -1;
+
+static int run_pre_command_hook(const char **argv)
+{
+	char *lock;
+	int ret = 0;
+
+	/*
+	 * Ensure the global pre/post command hook is only called for
+	 * the outer command and not when git is called recursively
+	 * or spawns multiple commands (like with the alias command)
+	 */
+	lock = getenv("COMMAND_HOOK_LOCK");
+	if (lock && !strcmp(lock, "true"))
+		return 0;
+	setenv("COMMAND_HOOK_LOCK", "true", 1);
+
+	/* call the hook proc */
+	argv_array_pushv(&sargv, argv);
+	argv_array_pushf(&sargv, "--git-pid=%"PRIuMAX, (uintmax_t)getpid());
+	ret = run_hook_argv(NULL, "pre-command", sargv.argv);
+
+	if (!ret)
+		run_post_hook = 1;
+	return ret;
+}
+
+static int run_post_command_hook(void)
+{
+	char *lock;
+	int ret = 0;
+
+	/*
+	 * Only run post_command if pre_command succeeded in this process
+	 */
+	if (!run_post_hook)
+		return 0;
+	lock = getenv("COMMAND_HOOK_LOCK");
+	if (!lock || strcmp(lock, "true"))
+		return 0;
+
+	argv_array_pushf(&sargv, "--exit_code=%u", exit_code);
+	ret = run_hook_argv(NULL, "post-command", sargv.argv);
+
+	run_post_hook = 0;
+	argv_array_clear(&sargv);
+	setenv("COMMAND_HOOK_LOCK", "false", 1);
+	return ret;
+}
+
+static void post_command_hook_atexit(void)
+{
+	run_post_command_hook();
+}
+
 static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 {
 	int status, help;
@@ -416,15 +490,25 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 	if (!help && p->option & NEED_WORK_TREE)
 		setup_work_tree();
 
+	if (!help && p->option & BLOCK_ON_GVFS_REPO && gvfs_config_is_set(GVFS_BLOCK_COMMANDS))
+		die("'git %s' is not supported on a GVFS repo", p->cmd);
+
+	if (run_pre_command_hook(argv))
+		die("pre-command hook aborted command");
+
 	trace_argv_printf(argv, "trace: built-in: git");
+	trace2_cmd_name(p->cmd);
+	trace2_cmd_list_config();
 
 	validate_cache_entries(the_repository->index);
-	status = p->fn(argc, argv, prefix);
+	exit_code = status = p->fn(argc, argv, prefix);
 	validate_cache_entries(the_repository->index);
 
 	if (status)
 		return status;
 
+	run_post_command_hook();
+
 	/* Somebody closed stdout? */
 	if (fstat(fileno(stdout), &st))
 		return 0;
@@ -483,7 +567,7 @@ static struct cmd_struct commands[] = {
 	{ "fmt-merge-msg", cmd_fmt_merge_msg, RUN_SETUP },
 	{ "for-each-ref", cmd_for_each_ref, RUN_SETUP },
 	{ "format-patch", cmd_format_patch, RUN_SETUP },
-	{ "fsck", cmd_fsck, RUN_SETUP },
+	{ "fsck", cmd_fsck, RUN_SETUP | BLOCK_ON_GVFS_REPO},
 	{ "fsck-objects", cmd_fsck, RUN_SETUP },
 	{ "gc", cmd_gc, RUN_SETUP },
 	{ "get-tar-commit-id", cmd_get_tar_commit_id, NO_PARSEOPT },
@@ -521,7 +605,7 @@ static struct cmd_struct commands[] = {
 	{ "pack-refs", cmd_pack_refs, RUN_SETUP },
 	{ "patch-id", cmd_patch_id, RUN_SETUP_GENTLY | NO_PARSEOPT },
 	{ "pickaxe", cmd_blame, RUN_SETUP },
-	{ "prune", cmd_prune, RUN_SETUP },
+	{ "prune", cmd_prune, RUN_SETUP | BLOCK_ON_GVFS_REPO},
 	{ "prune-packed", cmd_prune_packed, RUN_SETUP },
 	{ "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
 	{ "push", cmd_push, RUN_SETUP },
@@ -539,7 +623,7 @@ static struct cmd_struct commands[] = {
 	{ "remote", cmd_remote, RUN_SETUP },
 	{ "remote-ext", cmd_remote_ext, NO_PARSEOPT },
 	{ "remote-fd", cmd_remote_fd, NO_PARSEOPT },
-	{ "repack", cmd_repack, RUN_SETUP },
+	{ "repack", cmd_repack, RUN_SETUP | BLOCK_ON_GVFS_REPO },
 	{ "replace", cmd_replace, RUN_SETUP },
 	{ "rerere", cmd_rerere, RUN_SETUP },
 	{ "reset", cmd_reset, RUN_SETUP },
@@ -563,7 +647,7 @@ static struct cmd_struct commands[] = {
 	{ "stash", cmd_stash },
 	{ "status", cmd_status, RUN_SETUP | NEED_WORK_TREE },
 	{ "stripspace", cmd_stripspace },
-	{ "submodule--helper", cmd_submodule__helper, RUN_SETUP | SUPPORT_SUPER_PREFIX | NO_PARSEOPT },
+	{ "submodule--helper", cmd_submodule__helper, RUN_SETUP | SUPPORT_SUPER_PREFIX | NO_PARSEOPT | BLOCK_ON_GVFS_REPO },
 	{ "symbolic-ref", cmd_symbolic_ref, RUN_SETUP },
 	{ "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },
 	{ "unpack-file", cmd_unpack_file, RUN_SETUP | NO_PARSEOPT },
@@ -580,7 +664,7 @@ static struct cmd_struct commands[] = {
 	{ "verify-tag", cmd_verify_tag, RUN_SETUP },
 	{ "version", cmd_version },
 	{ "whatchanged", cmd_whatchanged, RUN_SETUP },
-	{ "worktree", cmd_worktree, RUN_SETUP | NO_PARSEOPT },
+	{ "worktree", cmd_worktree, RUN_SETUP | NO_PARSEOPT | BLOCK_ON_GVFS_REPO },
 	{ "write-tree", cmd_write_tree, RUN_SETUP },
 };
 
@@ -672,7 +756,17 @@ static void execv_dashed_external(const char **argv)
 	cmd.clean_on_exit = 1;
 	cmd.wait_after_clean = 1;
 	cmd.silent_exec_failure = 1;
+	cmd.trace2_child_class = "dashed";
+
+	if (run_pre_command_hook(cmd.args.argv))
+		die("pre-command hook aborted command");
 
+	trace2_cmd_name("_run_dashed_");
+
+	/*
+	 * The code in run_command() logs trace2 child_start/child_exit
+	 * events, so we do not need to report exec/exec_result events here.
+	 */
 	trace_argv_printf(cmd.args.argv, "trace: exec:");
 
 	/*
@@ -681,11 +775,19 @@ static void execv_dashed_external(const char **argv)
 	 * or our usual generic code if we were not even able to exec
 	 * the program.
 	 */
-	status = run_command(&cmd);
+	exit_code = status = run_command(&cmd);
+
+	/*
+	 * If the child process ran and we are now going to exit, emit a
+	 * generic string as our trace2 command verb to indicate that we
+	 * launched a dashed command.
+	 */
 	if (status >= 0)
 		exit(status);
 	else if (errno != ENOENT)
 		exit(128);
+
+	run_post_command_hook();
 }
 
 static int run_argv(int *argcp, const char ***argv)
@@ -710,6 +812,15 @@ static int run_argv(int *argcp, const char ***argv)
 			struct argv_array args = ARGV_ARRAY_INIT;
 			int i;
 
+			/*
+			 * The current process is committed to launching a
+			 * child process to run the command named in (**argv)
+			 * and exiting.  Log a generic string as the trace2
+			 * command verb to indicate this.  Note that the child
+			 * process will log the actual verb when it runs.
+			 */
+			trace2_cmd_name("_run_git_alias_");
+
 			if (get_super_prefix())
 				die("%s doesn't support --super-prefix", **argv);
 
@@ -725,8 +836,8 @@ static int run_argv(int *argcp, const char ***argv)
 			 * if we fail because the command is not found, it is
 			 * OK to return. Otherwise, we just pass along the status code.
 			 */
-			i = run_command_v_opt(args.argv, RUN_SILENT_EXEC_FAILURE |
-					      RUN_CLEAN_ON_EXIT);
+			i = run_command_v_opt_tr2(args.argv, RUN_SILENT_EXEC_FAILURE |
+						  RUN_CLEAN_ON_EXIT, "git_alias");
 			if (i >= 0 || errno != ENOENT)
 				exit(i);
 			die("could not execute builtin %s", **argv);
@@ -784,6 +895,7 @@ int cmd_main(int argc, const char **argv)
 	}
 
 	trace_command_performance(argv);
+	atexit(post_command_hook_atexit);
 
 	/*
 	 * "git-xxxx" is the same as "git xxxx", but we obviously:
@@ -811,10 +923,14 @@ int cmd_main(int argc, const char **argv)
 	} else {
 		/* The user didn't specify a command; give them help */
 		commit_pager_choice();
+		if (run_pre_command_hook(argv))
+			die("pre-command hook aborted command");
 		printf(_("usage: %s\n\n"), git_usage_string);
 		list_common_cmds_help();
 		printf("\n%s\n", _(git_more_info_string));
-		exit(1);
+		exit_code = 1;
+		run_post_command_hook();
+		exit(exit_code);
 	}
 	cmd = argv[0];
 
diff --git a/gvfs.c b/gvfs.c
new file mode 100644
index 00000000000000..7235199c04ac39
--- /dev/null
+++ b/gvfs.c
@@ -0,0 +1,38 @@
+#include "cache.h"
+#include "gvfs.h"
+#include "config.h"
+
+static int gvfs_config_loaded;
+static int core_gvfs_is_bool;
+
+static int early_core_gvfs_config(const char *var, const char *value, void *data)
+{
+	if (!strcmp(var, "core.gvfs"))
+		core_gvfs = git_config_bool_or_int("core.gvfs", value, &core_gvfs_is_bool);
+	return 0;
+}
+
+void gvfs_load_config_value(const char *value)
+{
+	if (gvfs_config_loaded)
+		return;
+
+	if (value)
+		core_gvfs = git_config_bool_or_int("core.gvfs", value, &core_gvfs_is_bool);
+	else if (startup_info->have_repository == 0)
+		read_early_config(early_core_gvfs_config, NULL);
+	else
+		git_config_get_bool_or_int("core.gvfs", &core_gvfs_is_bool, &core_gvfs);
+
+	/* Turn on all bits if a bool was set in the settings */
+	if (core_gvfs_is_bool && core_gvfs)
+		core_gvfs = -1;
+
+	gvfs_config_loaded = 1;
+}
+
+int gvfs_config_is_set(int mask)
+{
+	gvfs_load_config_value(0);
+	return (core_gvfs & mask) == mask;
+}
diff --git a/gvfs.h b/gvfs.h
new file mode 100644
index 00000000000000..e193502151467a
--- /dev/null
+++ b/gvfs.h
@@ -0,0 +1,24 @@
+#ifndef GVFS_H
+#define GVFS_H
+
+
+/*
+ * This file is for the specific settings and methods
+ * used for GVFS functionality
+ */
+
+
+/*
+ * The list of bits in the core_gvfs setting
+ */
+#define GVFS_SKIP_SHA_ON_INDEX                      (1 << 0)
+#define GVFS_BLOCK_COMMANDS                         (1 << 1)
+#define GVFS_MISSING_OK                             (1 << 2)
+#define GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT       (1 << 3)
+#define GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK (1 << 4)
+#define GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS      (1 << 6)
+
+void gvfs_load_config_value(const char *value);
+int gvfs_config_is_set(int mask);
+
+#endif /* GVFS_H */
diff --git a/kwset.c b/kwset.c
index 4fb6455acaf129..efc2ff41bc361a 100644
--- a/kwset.c
+++ b/kwset.c
@@ -38,7 +38,13 @@
 #include "compat/obstack.h"
 
 #define NCHAR (UCHAR_MAX + 1)
-#define obstack_chunk_alloc xmalloc
+/* adapter for `xmalloc()`, which takes `size_t`, not `long` */
+static void *obstack_chunk_alloc(long size)
+{
+	if (size < 0)
+		BUG("Cannot allocate a negative amount: %ld", size);
+	return xmalloc(size);
+}
 #define obstack_chunk_free free
 
 #define U(c) ((unsigned char) (c))
diff --git a/merge-recursive.c b/merge-recursive.c
index 255347d23ed261..5f5dba78cfea34 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -28,6 +28,7 @@
 #include "submodule.h"
 #include "revision.h"
 #include "commit-reach.h"
+#include "virtualfilesystem.h"
 
 struct path_hashmap_entry {
 	struct hashmap_entry e;
@@ -885,15 +886,14 @@ static int would_lose_untracked(struct merge_options *o, const char *path)
 static int was_dirty(struct merge_options *o, const char *path)
 {
 	struct cache_entry *ce;
-	int dirty = 1;
 
-	if (o->call_depth || !was_tracked(o, path))
-		return !dirty;
+	if (o->call_depth || !was_tracked(o, path) ||
+	    is_excluded_from_virtualfilesystem(path, strlen(path), DT_REG) == 1)
+		return 0;
 
 	ce = index_file_exists(o->unpack_opts.src_index,
 			       path, strlen(path), ignore_case);
-	dirty = verify_uptodate(ce, &o->unpack_opts) != 0;
-	return dirty;
+	return !ce || verify_uptodate(ce, &o->unpack_opts) != 0;
 }
 
 static int make_room_for_path(struct merge_options *o, const char *path)
@@ -1512,7 +1512,7 @@ static int handle_change_delete(struct merge_options *o,
 		 * path.  We could call update_file_flags() with update_cache=0
 		 * and update_wd=0, but that's a no-op.
 		 */
-		if (change_branch != o->branch1 || alt_path)
+		if (change_branch != o->branch1 || alt_path || !file_exists(update_path))
 			ret = update_file(o, 0, changed_oid, changed_mode, update_path);
 	}
 	free(alt_path);
diff --git a/midx.c b/midx.c
index 8a505fd423efcc..ffc1a16f0095f1 100644
--- a/midx.c
+++ b/midx.c
@@ -8,6 +8,8 @@
 #include "sha1-lookup.h"
 #include "midx.h"
 #include "progress.h"
+#include "run-command.h"
+#include "trace2.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -164,6 +166,9 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 			      m->pack_names[i]);
 	}
 
+	trace2_data_intmax("midx", the_repository, "load/num_packs", m->num_packs);
+	trace2_data_intmax("midx", the_repository, "load/num_objects", m->num_objects);
+
 	return m;
 
 cleanup_fail:
@@ -377,12 +382,26 @@ static size_t write_midx_header(struct hashfile *f,
 	return MIDX_HEADER_SIZE;
 }
 
+struct midx_info {
+	uint32_t orig_pack_int_id;
+	uint32_t new_pack_int_id;
+	char *pack_name;
+	struct packed_git *p;
+	unsigned expired : 1;
+};
+
+static int midx_info_compare(const void *_a, const void *_b)
+{
+	struct midx_info *a = (struct midx_info *)_a;
+	struct midx_info *b = (struct midx_info *)_b;
+	return strcmp(a->pack_name, b->pack_name);
+}
+
 struct pack_list {
-	struct packed_git **list;
-	char **names;
+	struct midx_info *info;
+	uint32_t *perm;
 	uint32_t nr;
-	uint32_t alloc_list;
-	uint32_t alloc_names;
+	uint32_t alloc;
 	size_t pack_name_concat_len;
 	struct multi_pack_index *m;
 };
@@ -396,67 +415,33 @@ static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 		if (packs->m && midx_contains_pack(packs->m, file_name))
 			return;
 
-		ALLOC_GROW(packs->list, packs->nr + 1, packs->alloc_list);
-		ALLOC_GROW(packs->names, packs->nr + 1, packs->alloc_names);
+		ALLOC_GROW(packs->info, packs->nr + 1, packs->alloc);
 
-		packs->list[packs->nr] = add_packed_git(full_path,
-							full_path_len,
-							0);
+		packs->info[packs->nr].p = add_packed_git(full_path,
+							   full_path_len,
+							   0);
+		packs->info[packs->nr].expired = 0;
 
-		if (!packs->list[packs->nr]) {
+		if (!packs->info[packs->nr].p) {
 			warning(_("failed to add packfile '%s'"),
 				full_path);
 			return;
 		}
 
-		if (open_pack_index(packs->list[packs->nr])) {
+		if (open_pack_index(packs->info[packs->nr].p)) {
 			warning(_("failed to open pack-index '%s'"),
 				full_path);
-			close_pack(packs->list[packs->nr]);
-			FREE_AND_NULL(packs->list[packs->nr]);
+			close_pack(packs->info[packs->nr].p);
+			FREE_AND_NULL(packs->info[packs->nr].p);
 			return;
 		}
 
-		packs->names[packs->nr] = xstrdup(file_name);
-		packs->pack_name_concat_len += strlen(file_name) + 1;
+		packs->info[packs->nr].pack_name = xstrdup(file_name);
+		packs->info[packs->nr].orig_pack_int_id = packs->nr;
 		packs->nr++;
 	}
 }
 
-struct pack_pair {
-	uint32_t pack_int_id;
-	char *pack_name;
-};
-
-static int pack_pair_compare(const void *_a, const void *_b)
-{
-	struct pack_pair *a = (struct pack_pair *)_a;
-	struct pack_pair *b = (struct pack_pair *)_b;
-	return strcmp(a->pack_name, b->pack_name);
-}
-
-static void sort_packs_by_name(char **pack_names, uint32_t nr_packs, uint32_t *perm)
-{
-	uint32_t i;
-	struct pack_pair *pairs;
-
-	ALLOC_ARRAY(pairs, nr_packs);
-
-	for (i = 0; i < nr_packs; i++) {
-		pairs[i].pack_int_id = i;
-		pairs[i].pack_name = pack_names[i];
-	}
-
-	QSORT(pairs, nr_packs, pack_pair_compare);
-
-	for (i = 0; i < nr_packs; i++) {
-		pack_names[i] = pairs[i].pack_name;
-		perm[pairs[i].pack_int_id] = i;
-	}
-
-	free(pairs);
-}
-
 struct pack_midx_entry {
 	struct object_id oid;
 	uint32_t pack_int_id;
@@ -482,7 +467,6 @@ static int midx_oid_compare(const void *_a, const void *_b)
 }
 
 static int nth_midxed_pack_midx_entry(struct multi_pack_index *m,
-				      uint32_t *pack_perm,
 				      struct pack_midx_entry *e,
 				      uint32_t pos)
 {
@@ -490,7 +474,7 @@ static int nth_midxed_pack_midx_entry(struct multi_pack_index *m,
 		return 1;
 
 	nth_midxed_object_oid(&e->oid, m, pos);
-	e->pack_int_id = pack_perm[nth_midxed_pack_int_id(m, pos)];
+	e->pack_int_id = nth_midxed_pack_int_id(m, pos);
 	e->offset = nth_midxed_offset(m, pos);
 
 	/* consider objects in midx to be from "old" packs */
@@ -524,8 +508,7 @@ static void fill_pack_entry(uint32_t pack_int_id,
  * of a packfile containing the object).
  */
 static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
-						  struct packed_git **p,
-						  uint32_t *perm,
+						  struct midx_info *info,
 						  uint32_t nr_packs,
 						  uint32_t *nr_objects)
 {
@@ -536,7 +519,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 	uint32_t start_pack = m ? m->num_packs : 0;
 
 	for (cur_pack = start_pack; cur_pack < nr_packs; cur_pack++)
-		total_objects += p[cur_pack]->num_objects;
+		total_objects += info[cur_pack].p->num_objects;
 
 	/*
 	 * As we de-duplicate by fanout value, we expect the fanout
@@ -561,7 +544,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 
 			for (cur_object = start; cur_object < end; cur_object++) {
 				ALLOC_GROW(entries_by_fanout, nr_fanout + 1, alloc_fanout);
-				nth_midxed_pack_midx_entry(m, perm,
+				nth_midxed_pack_midx_entry(m,
 							   &entries_by_fanout[nr_fanout],
 							   cur_object);
 				nr_fanout++;
@@ -572,12 +555,12 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 			uint32_t start = 0, end;
 
 			if (cur_fanout)
-				start = get_pack_fanout(p[cur_pack], cur_fanout - 1);
-			end = get_pack_fanout(p[cur_pack], cur_fanout);
+				start = get_pack_fanout(info[cur_pack].p, cur_fanout - 1);
+			end = get_pack_fanout(info[cur_pack].p, cur_fanout);
 
 			for (cur_object = start; cur_object < end; cur_object++) {
 				ALLOC_GROW(entries_by_fanout, nr_fanout + 1, alloc_fanout);
-				fill_pack_entry(perm[cur_pack], p[cur_pack], cur_object, &entries_by_fanout[nr_fanout]);
+				fill_pack_entry(cur_pack, info[cur_pack].p, cur_object, &entries_by_fanout[nr_fanout]);
 				nr_fanout++;
 			}
 		}
@@ -606,7 +589,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 }
 
 static size_t write_midx_pack_names(struct hashfile *f,
-				    char **pack_names,
+				    struct midx_info *info,
 				    uint32_t num_packs)
 {
 	uint32_t i;
@@ -614,14 +597,19 @@ static size_t write_midx_pack_names(struct hashfile *f,
 	size_t written = 0;
 
 	for (i = 0; i < num_packs; i++) {
-		size_t writelen = strlen(pack_names[i]) + 1;
+		size_t writelen;
+
+		if (info[i].expired)
+			continue;
 
-		if (i && strcmp(pack_names[i], pack_names[i - 1]) <= 0)
+		writelen = strlen(info[i].pack_name) + 1;
+
+		if (i && strcmp(info[i].pack_name, info[i - 1].pack_name) <= 0)
 			BUG("incorrect pack-file order: %s before %s",
-			    pack_names[i - 1],
-			    pack_names[i]);
+			    info[i - 1].pack_name,
+			    info[i].pack_name);
 
-		hashwrite(f, pack_names[i], writelen);
+		hashwrite(f, info[i].pack_name, writelen);
 		written += writelen;
 	}
 
@@ -692,6 +680,7 @@ static size_t write_midx_oid_lookup(struct hashfile *f, unsigned char hash_len,
 }
 
 static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_needed,
+					uint32_t *perm,
 					struct pack_midx_entry *objects, uint32_t nr_objects)
 {
 	struct pack_midx_entry *list = objects;
@@ -700,8 +689,13 @@ static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_nee
 
 	for (i = 0; i < nr_objects; i++) {
 		struct pack_midx_entry *obj = list++;
+		int pack_int_id = perm[obj->pack_int_id];
+
+		if (pack_int_id == UINT_MAX)
+			BUG("tried to write an object %s with expired pack-int-id",
+			    oid_to_hex(&obj->oid));
 
-		hashwrite_be32(f, obj->pack_int_id);
+		hashwrite_be32(f, pack_int_id);
 
 		if (large_offset_needed && obj->offset >> 31)
 			hashwrite_be32(f, MIDX_LARGE_OFFSET_NEEDED | nr_large_offset++);
@@ -747,21 +741,22 @@ static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_off
 	return written;
 }
 
-int write_midx_file(const char *object_dir)
+static int write_midx_internal(const char *object_dir, struct multi_pack_index *m,
+			       struct string_list *packs_to_drop)
 {
 	unsigned char cur_chunk, num_chunks = 0;
 	char *midx_name;
-	uint32_t i;
+	uint32_t i, drop_count;
 	struct hashfile *f = NULL;
 	struct lock_file lk;
 	struct pack_list packs;
-	uint32_t *pack_perm = NULL;
 	uint64_t written = 0;
 	uint32_t chunk_ids[MIDX_MAX_CHUNKS + 1];
 	uint64_t chunk_offsets[MIDX_MAX_CHUNKS + 1];
 	uint32_t nr_entries, num_large_offsets = 0;
 	struct pack_midx_entry *entries = NULL;
 	int large_offsets_needed = 0;
+	int result = 0;
 
 	midx_name = get_midx_filename(object_dir);
 	if (safe_create_leading_directories(midx_name)) {
@@ -770,42 +765,36 @@ int write_midx_file(const char *object_dir)
 			  midx_name);
 	}
 
-	packs.m = load_multi_pack_index(object_dir, 1);
+	if (m)
+		packs.m = m;
+	else
+		packs.m = load_multi_pack_index(object_dir, 1);
 
 	packs.nr = 0;
-	packs.alloc_list = packs.m ? packs.m->num_packs : 16;
-	packs.alloc_names = packs.alloc_list;
-	packs.list = NULL;
-	packs.names = NULL;
+	packs.alloc = packs.m ? packs.m->num_packs : 16;
+	packs.info = NULL;
+	packs.perm = NULL;
 	packs.pack_name_concat_len = 0;
-	ALLOC_ARRAY(packs.list, packs.alloc_list);
-	ALLOC_ARRAY(packs.names, packs.alloc_names);
+	ALLOC_ARRAY(packs.info, packs.alloc);
 
 	if (packs.m) {
 		for (i = 0; i < packs.m->num_packs; i++) {
-			ALLOC_GROW(packs.list, packs.nr + 1, packs.alloc_list);
-			ALLOC_GROW(packs.names, packs.nr + 1, packs.alloc_names);
+			ALLOC_GROW(packs.info, packs.nr + 1, packs.alloc);
 
-			packs.list[packs.nr] = NULL;
-			packs.names[packs.nr] = xstrdup(packs.m->pack_names[i]);
-			packs.pack_name_concat_len += strlen(packs.names[packs.nr]) + 1;
+			packs.info[packs.nr].pack_name = xstrdup(packs.m->pack_names[i]);
+			packs.info[packs.nr].orig_pack_int_id = i;
+			packs.info[packs.nr].p = NULL;
+			packs.info[packs.nr].expired = 0;
 			packs.nr++;
 		}
 	}
 
 	for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &packs);
 
-	if (packs.m && packs.nr == packs.m->num_packs)
+	if (packs.m && packs.nr == packs.m->num_packs && !packs_to_drop)
 		goto cleanup;
 
-	if (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
-		packs.pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
-					      (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT);
-
-	ALLOC_ARRAY(pack_perm, packs.nr);
-	sort_packs_by_name(packs.names, packs.nr, pack_perm);
-
-	entries = get_sorted_entries(packs.m, packs.list, pack_perm, packs.nr, &nr_entries);
+	entries = get_sorted_entries(packs.m, packs.info, packs.nr, &nr_entries);
 
 	for (i = 0; i < nr_entries; i++) {
 		if (entries[i].offset > 0x7fffffff)
@@ -814,6 +803,60 @@ int write_midx_file(const char *object_dir)
 			large_offsets_needed = 1;
 	}
 
+	QSORT(packs.info, packs.nr, midx_info_compare);
+
+	if (packs_to_drop && packs_to_drop->nr) {
+		int drop_index = 0;
+		int missing_drops = 0;
+
+		for (i = 0; i < packs.nr && drop_index < packs_to_drop->nr; i++) {
+			int cmp = strcmp(packs.info[i].pack_name,
+					 packs_to_drop->items[drop_index].string);
+
+			if (!cmp) {
+				drop_index++;
+				packs.info[i].expired = 1;
+			} else if (cmp > 0) {
+				error(_("did not see pack-file %s to drop"),
+				      packs_to_drop->items[drop_index].string);
+				drop_index++;
+				missing_drops++;
+				i--;
+			}
+		}
+
+		if (missing_drops) {
+			result = 1;
+			goto cleanup;
+		}
+	}
+
+	drop_count = 0;
+	for (i = 0; i < packs.nr; i++) {
+		if (packs.info[i].expired)
+			drop_count++;
+		else
+			packs.info[i].new_pack_int_id = i - drop_count;
+	}
+
+	packs.perm = xcalloc(packs.nr, sizeof(uint32_t));
+	for (i = 0; i < packs.nr; i++) {
+		if (packs.info[i].expired)
+			packs.perm[packs.info[i].orig_pack_int_id] = UINT_MAX;
+		else
+			packs.perm[packs.info[i].orig_pack_int_id] =
+				packs.info[i].new_pack_int_id;
+	}
+
+	for (i = 0; i < packs.nr; i++) {
+		if (!packs.info[i].expired)
+			packs.pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+	}
+
+	if (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
+		packs.pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
+					      (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT);
+
 	hold_lock_file_for_update(&lk, midx_name, LOCK_DIE_ON_ERROR);
 	f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
 	FREE_AND_NULL(midx_name);
@@ -824,7 +867,7 @@ int write_midx_file(const char *object_dir)
 	cur_chunk = 0;
 	num_chunks = large_offsets_needed ? 5 : 4;
 
-	written = write_midx_header(f, num_chunks, packs.nr);
+	written = write_midx_header(f, num_chunks, packs.nr - drop_count);
 
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
 	chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
@@ -879,7 +922,7 @@ int write_midx_file(const char *object_dir)
 
 		switch (chunk_ids[i]) {
 			case MIDX_CHUNKID_PACKNAMES:
-				written += write_midx_pack_names(f, packs.names, packs.nr);
+				written += write_midx_pack_names(f, packs.info, packs.nr);
 				break;
 
 			case MIDX_CHUNKID_OIDFANOUT:
@@ -891,7 +934,7 @@ int write_midx_file(const char *object_dir)
 				break;
 
 			case MIDX_CHUNKID_OBJECTOFFSETS:
-				written += write_midx_object_offsets(f, large_offsets_needed, entries, nr_entries);
+				written += write_midx_object_offsets(f, large_offsets_needed, packs.perm, entries, nr_entries);
 				break;
 
 			case MIDX_CHUNKID_LARGEOFFSETS:
@@ -914,19 +957,23 @@ int write_midx_file(const char *object_dir)
 
 cleanup:
 	for (i = 0; i < packs.nr; i++) {
-		if (packs.list[i]) {
-			close_pack(packs.list[i]);
-			free(packs.list[i]);
+		if (packs.info[i].p) {
+			close_pack(packs.info[i].p);
+			free(packs.info[i].p);
 		}
-		free(packs.names[i]);
+		free(packs.info[i].pack_name);
 	}
 
-	free(packs.list);
-	free(packs.names);
+	free(packs.info);
+	free(packs.perm);
 	free(entries);
-	free(pack_perm);
 	free(midx_name);
-	return 0;
+	return result;
+}
+
+int write_midx_file(const char *object_dir)
+{
+	return write_midx_internal(object_dir, NULL, NULL);
 }
 
 void clear_midx_file(struct repository *r)
@@ -958,8 +1005,35 @@ static void midx_report(const char *fmt, ...)
 	va_end(ap);
 }
 
+struct pair_pos_vs_id
+{
+	uint32_t pos;
+	uint32_t pack_int_id;
+};
+
+static int compare_pair_pos_vs_id(const void *_a, const void *_b)
+{
+	struct pair_pos_vs_id *a = (struct pair_pos_vs_id *)_a;
+	struct pair_pos_vs_id *b = (struct pair_pos_vs_id *)_b;
+
+	return b->pack_int_id - a->pack_int_id;
+}
+
+/*
+ * Limit calls to display_progress() for performance reasons.
+ * The interval here was arbitrarily chosen.
+ */
+#define SPARSE_PROGRESS_INTERVAL (1 << 12)
+#define midx_display_sparse_progress(progress, n) \
+	do { \
+		uint64_t _n = (n); \
+		if ((_n & (SPARSE_PROGRESS_INTERVAL - 1)) == 0) \
+			display_progress(progress, _n); \
+	} while (0)
+
 int verify_midx_file(const char *object_dir)
 {
+	struct pair_pos_vs_id *pairs = NULL;
 	uint32_t i;
 	struct progress *progress;
 	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
@@ -968,10 +1042,15 @@ int verify_midx_file(const char *object_dir)
 	if (!m)
 		return 0;
 
+	progress = start_progress(_("Looking for referenced packfiles"),
+				  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		if (prepare_midx_pack(m, i))
 			midx_report("failed to load pack in position %d", i);
+
+		display_progress(progress, i + 1);
 	}
+	stop_progress(&progress);
 
 	for (i = 0; i < 255; i++) {
 		uint32_t oid_fanout1 = ntohl(m->chunk_oid_fanout[i]);
@@ -982,6 +1061,8 @@ int verify_midx_file(const char *object_dir)
 				    i, oid_fanout1, oid_fanout2, i + 1);
 	}
 
+	progress = start_sparse_progress(_("Verifying OID order in MIDX"),
+					 m->num_objects - 1);
 	for (i = 0; i < m->num_objects - 1; i++) {
 		struct object_id oid1, oid2;
 
@@ -991,18 +1072,47 @@ int verify_midx_file(const char *object_dir)
 		if (oidcmp(&oid1, &oid2) >= 0)
 			midx_report(_("oid lookup out of order: oid[%d] = %s >= %s = oid[%d]"),
 				    i, oid_to_hex(&oid1), oid_to_hex(&oid2), i + 1);
+
+		midx_display_sparse_progress(progress, i + 1);
+	}
+	stop_progress(&progress);
+
+	/*
+	 * Create an array mapping each object to its packfile id.  Sort it
+	 * to group the objects by packfile.  Use this permutation to visit
+	 * each of the objects and only require 1 packfile to be open at a
+	 * time.
+	 */
+	ALLOC_ARRAY(pairs, m->num_objects);
+	for (i = 0; i < m->num_objects; i++) {
+		pairs[i].pos = i;
+		pairs[i].pack_int_id = nth_midxed_pack_int_id(m, i);
 	}
 
-	progress = start_progress(_("Verifying object offsets"), m->num_objects);
+	progress = start_sparse_progress(_("Sorting objects by packfile"),
+					 m->num_objects);
+	display_progress(progress, 0); /* TODO: Measure QSORT() progress */
+	QSORT(pairs, m->num_objects, compare_pair_pos_vs_id);
+	stop_progress(&progress);
+
+	progress = start_sparse_progress(_("Verifying object offsets"), m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
 		struct object_id oid;
 		struct pack_entry e;
 		off_t m_offset, p_offset;
 
-		nth_midxed_object_oid(&oid, m, i);
+		if (i > 0 && pairs[i-1].pack_int_id != pairs[i].pack_int_id &&
+		    m->packs[pairs[i-1].pack_int_id])
+		{
+			close_pack_fd(m->packs[pairs[i-1].pack_int_id]);
+			close_pack_index(m->packs[pairs[i-1].pack_int_id]);
+		}
+
+		nth_midxed_object_oid(&oid, m, pairs[i].pos);
+
 		if (!fill_midx_entry(&oid, &e, m)) {
 			midx_report(_("failed to load pack entry for oid[%d] = %s"),
-				    i, oid_to_hex(&oid));
+				    pairs[i].pos, oid_to_hex(&oid));
 			continue;
 		}
 
@@ -1017,11 +1127,169 @@ int verify_midx_file(const char *object_dir)
 
 		if (m_offset != p_offset)
 			midx_report(_("incorrect object offset for oid[%d] = %s: %"PRIx64" != %"PRIx64),
-				    i, oid_to_hex(&oid), m_offset, p_offset);
+				    pairs[i].pos, oid_to_hex(&oid), m_offset, p_offset);
 
-		display_progress(progress, i + 1);
+		midx_display_sparse_progress(progress, i + 1);
 	}
 	stop_progress(&progress);
 
+	free(pairs);
+
 	return verify_midx_error;
 }
+
+int expire_midx_packs(const char *object_dir)
+{
+	uint32_t i, *count, result = 0;
+	struct string_list packs_to_drop = STRING_LIST_INIT_DUP;
+	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+	if (!m)
+		return 0;
+
+	count = xcalloc(m->num_packs, sizeof(uint32_t));
+	for (i = 0; i < m->num_objects; i++) {
+		int pack_int_id = nth_midxed_pack_int_id(m, i);
+		count[pack_int_id]++;
+	}
+
+	for (i = 0; i < m->num_packs; i++) {
+		char *pack_name;
+
+		if (count[i])
+			continue;
+
+		if (prepare_midx_pack(m, i))
+			continue;
+
+		if (m->packs[i]->pack_keep)
+			continue;
+
+		pack_name = xstrdup(m->packs[i]->pack_name);
+		close_pack(m->packs[i]);
+		FREE_AND_NULL(m->packs[i]);
+
+		string_list_insert(&packs_to_drop, m->pack_names[i]);
+		unlink_pack_path(pack_name, 0);
+		free(pack_name);
+	}
+
+	free(count);
+
+	if (packs_to_drop.nr)
+		result = write_midx_internal(object_dir, m, &packs_to_drop);
+
+	string_list_clear(&packs_to_drop, 0);
+	return result;
+}
+
+struct time_and_id {
+	timestamp_t mtime;
+	uint32_t pack_int_id;
+};
+
+static int compare_by_mtime(const void *a_, const void *b_)
+{
+	const struct time_and_id *a, *b;
+
+	a = (const struct time_and_id *)a_;
+	b = (const struct time_and_id *)b_;
+
+	if (a->mtime < b->mtime)
+		return -1;
+	if (a->mtime > b->mtime)
+		return 1;
+	return 0;
+}
+
+int midx_repack(const char *object_dir, size_t batch_size)
+{
+	int result = 0;
+	uint32_t i, packs_to_repack;
+	size_t total_size;
+	struct time_and_id *pack_ti;
+	unsigned char *include_pack;
+	struct child_process cmd = CHILD_PROCESS_INIT;
+	struct strbuf base_name = STRBUF_INIT;
+	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+	if (!m)
+		return 0;
+
+	include_pack = xcalloc(m->num_packs, sizeof(unsigned char));
+	pack_ti = xcalloc(m->num_packs, sizeof(struct time_and_id));
+
+	for (i = 0; i < m->num_packs; i++) {
+		pack_ti[i].pack_int_id = i;
+
+		if (prepare_midx_pack(m, i))
+			continue;
+
+		pack_ti[i].mtime = m->packs[i]->mtime;
+	}
+	QSORT(pack_ti, m->num_packs, compare_by_mtime);
+
+	total_size = 0;
+	packs_to_repack = 0;
+	for (i = 0; total_size < batch_size && i < m->num_packs; i++) {
+		int pack_int_id = pack_ti[i].pack_int_id;
+		struct packed_git *p = m->packs[pack_int_id];
+
+		if (!p)
+			continue;
+		if (p->pack_size >= batch_size)
+			continue;
+
+		packs_to_repack++;
+		total_size += p->pack_size;
+		include_pack[pack_int_id] = 1;
+	}
+
+	if (total_size < batch_size || packs_to_repack < 2)
+		goto cleanup;
+
+	argv_array_push(&cmd.args, "pack-objects");
+
+	strbuf_addstr(&base_name, object_dir);
+	strbuf_addstr(&base_name, "/pack/pack");
+	argv_array_push(&cmd.args, base_name.buf);
+	strbuf_release(&base_name);
+
+	cmd.git_cmd = 1;
+	cmd.in = cmd.out = -1;
+
+	if (start_command(&cmd)) {
+		error(_("could not start pack-objects"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for (i = 0; i < m->num_objects; i++) {
+		struct object_id oid;
+		uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
+
+		if (!include_pack[pack_int_id])
+			continue;
+
+		nth_midxed_object_oid(&oid, m, i);
+		xwrite(cmd.in, oid_to_hex(&oid), the_hash_algo->hexsz);
+		xwrite(cmd.in, "\n", 1);
+	}
+	close(cmd.in);
+
+	if (finish_command(&cmd)) {
+		error(_("could not finish pack-objects"));
+		result = 1;
+		goto cleanup;
+	}
+
+	result = write_midx_internal(object_dir, m, NULL);
+	m = NULL;
+
+cleanup:
+	if (m)
+		close_midx(m);
+	free(include_pack);
+	free(pack_ti);
+	return result;
+}
diff --git a/midx.h b/midx.h
index 774f652530c429..394a21ee96f0fd 100644
--- a/midx.h
+++ b/midx.h
@@ -49,6 +49,8 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 int write_midx_file(const char *object_dir);
 void clear_midx_file(struct repository *r);
 int verify_midx_file(const char *object_dir);
+int expire_midx_packs(const char *object_dir);
+int midx_repack(const char *object_dir, size_t batch_size);
 
 void close_midx(struct multi_pack_index *m);
 
diff --git a/packfile.c b/packfile.c
index 16bcb75262d918..498498b1e36679 100644
--- a/packfile.c
+++ b/packfile.c
@@ -309,7 +309,7 @@ void close_pack_windows(struct packed_git *p)
 	}
 }
 
-static int close_pack_fd(struct packed_git *p)
+int close_pack_fd(struct packed_git *p)
 {
 	if (p->pack_fd < 0)
 		return 0;
@@ -352,6 +352,34 @@ void close_all_packs(struct raw_object_store *o)
 	}
 }
 
+void unlink_pack_path(const char *pack_name, int force_delete)
+{
+	static const char *exts[] = {".pack", ".idx", ".keep", ".bitmap", ".promisor"};
+	int i;
+	struct strbuf buf = STRBUF_INIT;
+	size_t plen;
+
+	strbuf_addstr(&buf, pack_name);
+	strip_suffix_mem(buf.buf, &buf.len, ".pack");
+	plen = buf.len;
+
+	if (!force_delete) {
+		strbuf_addstr(&buf, ".keep");
+		if (!access(buf.buf, F_OK)) {
+			strbuf_release(&buf);
+			return;
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(exts); i++) {
+		strbuf_setlen(&buf, plen);
+		strbuf_addstr(&buf, exts[i]);
+		unlink(buf.buf);
+	}
+
+	strbuf_release(&buf);
+}
+
 /*
  * The LRU pack is the one with the oldest MRU window, preferring packs
  * with no used windows, or the oldest mtime if it has no windows allocated.
diff --git a/packfile.h b/packfile.h
index d70c6d9afb94c7..f5f530b63649e6 100644
--- a/packfile.h
+++ b/packfile.h
@@ -76,6 +76,8 @@ extern int open_pack_index(struct packed_git *);
  */
 extern void close_pack_index(struct packed_git *);
 
+int close_pack_fd(struct packed_git *p);
+
 extern uint32_t get_pack_fanout(struct packed_git *p, uint32_t value);
 
 extern unsigned char *use_pack(struct packed_git *, struct pack_window **, off_t, unsigned long *);
@@ -86,6 +88,13 @@ extern void unuse_pack(struct pack_window **);
 extern void clear_delta_base_cache(void);
 extern struct packed_git *add_packed_git(const char *path, size_t path_len, int local);
 
+/*
+ * Unlink the .pack and associated extension files.
+ * Does not unlink if 'force_delete' is false and the pack-file is
+ * marked as ".keep".
+ */
+extern void unlink_pack_path(const char *pack_name, int force_delete);
+
 /*
  * Make sure that a pointer access into an mmap'd index file is within bounds,
  * and can provide at least 8 bytes of data.
diff --git a/pager.c b/pager.c
index a768797fcfcc44..4168460ae92ceb 100644
--- a/pager.c
+++ b/pager.c
@@ -100,6 +100,7 @@ void prepare_pager_args(struct child_process *pager_process, const char *pager)
 	argv_array_push(&pager_process->args, pager);
 	pager_process->use_shell = 1;
 	setup_pager_env(&pager_process->env_array);
+	pager_process->trace2_child_class = "pager";
 }
 
 void setup_pager(void)
diff --git a/pkt-line.c b/pkt-line.c
index d4b71d3e82b0e5..acb5583c01b65f 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -88,13 +88,15 @@ static void packet_trace(const char *buf, unsigned int len, int write)
 void packet_flush(int fd)
 {
 	packet_trace("0000", 4, 1);
-	write_or_die(fd, "0000", 4);
+	if (write_in_full(fd, "0000", 4) < 0)
+		die_errno(_("unable to write flush packet"));
 }
 
 void packet_delim(int fd)
 {
 	packet_trace("0001", 4, 1);
-	write_or_die(fd, "0001", 4);
+	if (write_in_full(fd, "0001", 4) < 0)
+		die_errno(_("unable to write delim packet"));
 }
 
 int packet_flush_gently(int fd)
@@ -185,7 +187,7 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
 	return status;
 }
 
-static int packet_write_gently(const int fd_out, const char *buf, size_t size)
+int packet_write_gently(const int fd_out, const char *buf, size_t size)
 {
 	static char packet_write_buffer[LARGE_PACKET_MAX];
 	size_t packet_size;
diff --git a/pkt-line.h b/pkt-line.h
index ad9a4a2cd7c332..aaf6442a01ddb7 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -30,6 +30,7 @@ void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((f
 void packet_buf_write_len(struct strbuf *buf, const char *data, size_t len);
 int packet_flush_gently(int fd);
 int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
+int packet_write_gently(const int fd_out, const char *buf, size_t size);
 int write_packetized_from_fd(int fd_in, int fd_out);
 int write_packetized_from_buf(const char *src_in, size_t len, int fd_out);
 
diff --git a/progress.c b/progress.c
index 5a99c9fbf00bfb..212d00e524819a 100644
--- a/progress.c
+++ b/progress.c
@@ -34,6 +34,7 @@ struct progress {
 	uint64_t total;
 	unsigned last_percent;
 	unsigned delay;
+	unsigned sparse;
 	struct throughput *throughput;
 	uint64_t start_ns;
 };
@@ -194,7 +195,7 @@ int display_progress(struct progress *progress, uint64_t n)
 }
 
 static struct progress *start_progress_delay(const char *title, uint64_t total,
-					     unsigned delay)
+					     unsigned delay, unsigned sparse)
 {
 	struct progress *progress = malloc(sizeof(*progress));
 	if (!progress) {
@@ -208,6 +209,7 @@ static struct progress *start_progress_delay(const char *title, uint64_t total,
 	progress->last_value = -1;
 	progress->last_percent = -1;
 	progress->delay = delay;
+	progress->sparse = sparse;
 	progress->throughput = NULL;
 	progress->start_ns = getnanotime();
 	set_progress_signal();
@@ -216,16 +218,46 @@ static struct progress *start_progress_delay(const char *title, uint64_t total,
 
 struct progress *start_delayed_progress(const char *title, uint64_t total)
 {
-	return start_progress_delay(title, total, 2);
+	return start_progress_delay(title, total, 2, 0);
 }
 
 struct progress *start_progress(const char *title, uint64_t total)
 {
-	return start_progress_delay(title, total, 0);
+	return start_progress_delay(title, total, 0, 0);
+}
+
+/*
+ * Here "sparse" means that the caller might use some sampling criteria to
+ * decide when to call display_progress() rather than calling it for every
+ * integer value in[0 .. total).  In particular, the caller might not call
+ * display_progress() for the last value in the range.
+ *
+ * When "sparse" is set, stop_progress() will automatically force the done
+ * message to show 100%.
+ */
+struct progress *start_sparse_progress(const char *title, uint64_t total)
+{
+	return start_progress_delay(title, total, 0, 1);
+}
+
+struct progress *start_delayed_sparse_progress(const char *title,
+					       uint64_t total)
+{
+	return start_progress_delay(title, total, 2, 1);
+}
+
+static void finish_if_sparse(struct progress *progress)
+{
+	if (progress &&
+	    progress->sparse &&
+	    progress->last_value != progress->total)
+		display_progress(progress, progress->total);
 }
 
 void stop_progress(struct progress **p_progress)
 {
+	finish_if_sparse(*p_progress);
+
 	stop_progress_msg(p_progress, _("done"));
 }
 
diff --git a/progress.h b/progress.h
index 70a4d4a0d66ebd..7b725acc8d7b6c 100644
--- a/progress.h
+++ b/progress.h
@@ -6,7 +6,10 @@ struct progress;
 void display_throughput(struct progress *progress, uint64_t total);
 int display_progress(struct progress *progress, uint64_t n);
 struct progress *start_progress(const char *title, uint64_t total);
+struct progress *start_sparse_progress(const char *title, uint64_t total);
 struct progress *start_delayed_progress(const char *title, uint64_t total);
+struct progress *start_delayed_sparse_progress(const char *title,
+					       uint64_t total);
 void stop_progress(struct progress **progress);
 void stop_progress_msg(struct progress **progress, const char *msg);
 
diff --git a/read-cache.c b/read-cache.c
index bbcf488c20a483..a880aaedffbc5e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -17,6 +17,7 @@
 #include "commit.h"
 #include "blob.h"
 #include "resolve-undo.h"
+#include "run-command.h"
 #include "strbuf.h"
 #include "varint.h"
 #include "split-index.h"
@@ -24,6 +25,8 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "virtualfilesystem.h"
+#include "gvfs.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -1885,6 +1888,7 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_untracked_cache(istate);
 	tweak_split_index(istate);
 	tweak_fsmonitor(istate);
+	apply_virtualfilesystem(istate);
 }
 
 static size_t estimate_cache_size_from_compressed(unsigned int entries)
@@ -2222,6 +2226,16 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		load_index_extensions(&p);
 	}
 	munmap((void *)mmap, mmap_size);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "read/version",
+			   istate->version);
+	trace2_data_intmax("index", the_repository, "read/cache_nr",
+			   istate->cache_nr);
+
 	return istate->cache_nr;
 
 unmap:
@@ -2253,9 +2267,17 @@ int read_index_from(struct index_state *istate, const char *path,
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 	trace_performance_enter();
 	ret = do_read_index(istate, path, 0);
 	trace_performance_leave("read cache %s", path);
+	trace2_region_leave_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 
 	split_index = istate->split_index;
 	if (!split_index || is_null_oid(&split_index->base_oid)) {
@@ -2271,7 +2293,11 @@ int read_index_from(struct index_state *istate, const char *path,
 
 	base_oid_hex = oid_to_hex(&split_index->base_oid);
 	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
+	trace2_region_enter_printf("index", "shared/do_read_index",
+				   the_repository, "%s", base_path);
 	ret = do_read_index(split_index->base, base_path, 1);
+	trace2_region_leave_printf("index", "shared/do_read_index",
+				   the_repository, "%s", base_path);
 	if (!oideq(&split_index->base_oid, &split_index->base->oid))
 		die(_("broken index, expect %s in %s, got %s"),
 		    base_oid_hex, base_path,
@@ -2409,7 +2435,9 @@ static int ce_write_flush(git_hash_ctx *context, int fd)
 {
 	unsigned int buffered = write_buffer_len;
 	if (buffered) {
-		the_hash_algo->update_fn(context, write_buffer, buffered);
+		if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+			the_hash_algo->update_fn(context, write_buffer,
+						 buffered);
 		if (write_in_full(fd, write_buffer, buffered) < 0)
 			return -1;
 		write_buffer_len = 0;
@@ -2458,7 +2486,8 @@ static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
 
 	if (left) {
 		write_buffer_len = 0;
-		the_hash_algo->update_fn(context, write_buffer, left);
+		if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+			the_hash_algo->update_fn(context, write_buffer, left);
 	}
 
 	/* Flush first if not enough space for hash signature */
@@ -2469,7 +2498,8 @@ static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
 	}
 
 	/* Append the hash signature at the end */
-	the_hash_algo->final_fn(write_buffer + left, context);
+	if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+		the_hash_algo->final_fn(write_buffer + left, context);
 	hashcpy(hash, write_buffer + left);
 	left += the_hash_algo->rawsz;
 	return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 0;
@@ -2978,6 +3008,16 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	istate->timestamp.sec = (unsigned int)st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 	trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "write/version",
+			   istate->version);
+	trace2_data_intmax("index", the_repository, "write/cache_nr",
+			   istate->cache_nr);
+
 	return 0;
 }
 
@@ -2997,12 +3037,32 @@ static int commit_locked_index(struct lock_file *lk)
 static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
 				 unsigned flags)
 {
-	int ret = do_write_index(istate, lock->tempfile, 0);
+	int ret;
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+	ret = do_write_index(istate, lock->tempfile, 0);
+	trace2_region_leave_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+
 	if (ret)
 		return ret;
 	if (flags & COMMIT_LOCK)
-		return commit_locked_index(lock);
-	return close_lock_file_gently(lock);
+		ret = commit_locked_index(lock);
+	else
+		ret = close_lock_file_gently(lock);
+
+	run_hook_le(NULL, "post-indexchanged",
+			istate->updated_workdir ? "1" : "0",
+			istate->updated_skipworktree ? "1" : "0", NULL);
+	istate->updated_workdir = 0;
+	istate->updated_skipworktree = 0;
+
+	return ret;
 }
 
 static int write_split_index(struct index_state *istate,
@@ -3082,7 +3142,13 @@ static int write_shared_index(struct index_state *istate,
 	int ret;
 
 	move_cache_to_base_index(istate);
+
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
 	ret = do_write_index(si->base, *temp, 1);
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
+
 	if (ret)
 		return ret;
 	ret = adjust_shared_perm(get_tempfile_path(*temp));
diff --git a/remote-curl.c b/remote-curl.c
index bb7421023ba584..aad02dcc74b61d 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -1385,6 +1385,13 @@ int cmd_main(int argc, const char **argv)
 	string_list_init(&options.deepen_not, 1);
 	string_list_init(&options.push_options, 1);
 
+	/*
+	 * Just report "remote-curl" here (folding all the various aliases
+	 * ("git-remote-http", "git-remote-https", and etc.) here since they
+	 * are all just copies of the same actual executable.
+	 */
+	trace2_cmd_name("remote-curl");
+
 	remote = remote_get(argv[1]);
 
 	if (argc > 2) {
diff --git a/repository.c b/repository.c
index 65e6f8b8fdfcf8..5cad2dcc86a530 100644
--- a/repository.c
+++ b/repository.c
@@ -126,6 +126,8 @@ static int repo_init_gitdir(struct repository *repo, const char *gitdir)
 void repo_set_worktree(struct repository *repo, const char *path)
 {
 	repo->worktree = real_pathdup(path, 1);
+
+	trace2_def_repo(repo);
 }
 
 static int read_and_verify_repository_format(struct repository_format *format,
diff --git a/repository.h b/repository.h
index 8981649d43736e..4fb6a5885f794d 100644
--- a/repository.h
+++ b/repository.h
@@ -92,6 +92,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* A unique-id for tracing purposes. */
+	int trace2_repo_id;
+
 	/* Configurations */
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */
diff --git a/run-command.c b/run-command.c
index 3db26b7b0e2ab9..296e2c4d487f4c 100644
--- a/run-command.c
+++ b/run-command.c
@@ -7,6 +7,7 @@
 #include "strbuf.h"
 #include "string-list.h"
 #include "quote.h"
+#include "config.h"
 
 void child_process_init(struct child_process *child)
 {
@@ -219,9 +220,29 @@ static int exists_in_PATH(const char *file)
 
 int sane_execvp(const char *file, char * const argv[])
 {
+#ifndef GIT_WINDOWS_NATIVE
+	/*
+	 * execvp() doesn't return, so we all we can do is tell trace2
+	 * what we are about to do and let it leave a hint in the log
+	 * (unless of course the execvp() fails).
+	 *
+	 * we skip this for Windows because the compat layer already
+	 * has to emulate the execvp() call anyway.
+	 */
+	int exec_id = trace2_exec(file, (const char **)argv);
+#endif
+
 	if (!execvp(file, argv))
 		return 0; /* cannot happen ;-) */
 
+#ifndef GIT_WINDOWS_NATIVE
+	{
+		int ec = errno;
+		trace2_exec_result(exec_id, ec);
+		errno = ec;
+	}
+#endif
+
 	/*
 	 * When a command can't be found because one of the directories
 	 * listed in $PATH is unsearchable, execvp reports EACCES, but
@@ -712,6 +733,7 @@ int start_command(struct child_process *cmd)
 		cmd->err = fderr[0];
 	}
 
+	trace2_child_start(cmd);
 	trace_run_command(cmd);
 
 	fflush(NULL);
@@ -926,6 +948,8 @@ int start_command(struct child_process *cmd)
 #endif
 
 	if (cmd->pid < 0) {
+		trace2_child_exit(cmd, -1);
+
 		if (need_in)
 			close_pair(fdin);
 		else if (cmd->in)
@@ -964,13 +988,16 @@ int start_command(struct child_process *cmd)
 int finish_command(struct child_process *cmd)
 {
 	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 0);
+	trace2_child_exit(cmd, ret);
 	child_process_clear(cmd);
 	return ret;
 }
 
 int finish_command_in_signal(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	trace2_child_exit(cmd, ret);
+	return ret;
 }
 
 
@@ -992,7 +1019,18 @@ int run_command_v_opt(const char **argv, int opt)
 	return run_command_v_opt_cd_env(argv, opt, NULL, NULL);
 }
 
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, NULL, NULL, tr2_class);
+}
+
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, dir, env, NULL);
+}
+
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir,
+				 const char *const *env, const char *tr2_class)
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	cmd.argv = argv;
@@ -1004,6 +1042,7 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
 	cmd.clean_on_exit = opt & RUN_CLEAN_ON_EXIT ? 1 : 0;
 	cmd.dir = dir;
 	cmd.env = env;
+	cmd.trace2_child_class = tr2_class;
 	return run_command(&cmd);
 }
 
@@ -1270,12 +1309,69 @@ int async_with_fork(void)
 #endif
 }
 
+static int early_hooks_path_config(const char *var, const char *value, void *data)
+{
+	if (!strcmp(var, "core.hookspath"))
+		return git_config_pathname((const char **)data, var, value);
+
+	return 0;
+}
+
+/* Discover the hook before setup_git_directory() was called */
+static const char *hook_path_early(const char *name, struct strbuf *result)
+{
+	static struct strbuf hooks_dir = STRBUF_INIT;
+	static int initialized;
+
+	if (initialized < 0)
+		return NULL;
+
+	if (!initialized) {
+		struct strbuf gitdir = STRBUF_INIT, commondir = STRBUF_INIT;
+		const char *early_hooks_dir = NULL;
+
+		if (discover_git_directory(&commondir, &gitdir) < 0) {
+			initialized = -1;
+			return NULL;
+		}
+
+		read_early_config(early_hooks_path_config, &early_hooks_dir);
+		if (!early_hooks_dir)
+			strbuf_addf(&hooks_dir, "%s/hooks/", commondir.buf);
+		else {
+			strbuf_add_absolute_path(&hooks_dir, early_hooks_dir);
+			strbuf_addch(&hooks_dir, '/');
+		}
+
+		strbuf_release(&gitdir);
+		strbuf_release(&commondir);
+
+		initialized = 1;
+	}
+
+	strbuf_addf(result, "%s%s", hooks_dir.buf, name);
+	return result->buf;
+}
+
 const char *find_hook(const char *name)
 {
 	static struct strbuf path = STRBUF_INIT;
 
 	strbuf_reset(&path);
-	strbuf_git_path(&path, "hooks/%s", name);
+	if (have_git_dir()) {
+		static int forced_config;
+
+		if (!forced_config) {
+			if (!git_hooks_path)
+				git_config_get_pathname("core.hookspath",
+							&git_hooks_path);
+			forced_config = 1;
+		}
+
+		strbuf_git_path(&path, "hooks/%s", name);
+	} else if (!hook_path_early(name, &path))
+		return NULL;
+
 	if (access(path.buf, X_OK) < 0) {
 		int err = errno;
 
@@ -1304,7 +1400,8 @@ const char *find_hook(const char *name)
 	return path.buf;
 }
 
-int run_hook_ve(const char *const *env, const char *name, va_list args)
+int run_hook_argv(const char *const *env, const char *name,
+		  const char **argv)
 {
 	struct child_process hook = CHILD_PROCESS_INIT;
 	const char *p;
@@ -1314,15 +1411,29 @@ int run_hook_ve(const char *const *env, const char *name, va_list args)
 		return 0;
 
 	argv_array_push(&hook.args, p);
-	while ((p = va_arg(args, const char *)))
-		argv_array_push(&hook.args, p);
+	argv_array_pushv(&hook.args, argv);
 	hook.env = env;
 	hook.no_stdin = 1;
 	hook.stdout_to_stderr = 1;
+	hook.trace2_hook_name = name;
 
 	return run_command(&hook);
 }
 
+int run_hook_ve(const char *const *env, const char *name, va_list args)
+{
+	struct argv_array argv = ARGV_ARRAY_INIT;
+	const char *p;
+	int ret;
+
+	while ((p = va_arg(args, const char *)))
+		argv_array_push(&argv, p);
+
+	ret = run_hook_argv(env, name, argv.argv);
+	argv_array_clear(&argv);
+	return ret;
+}
+
 int run_hook_le(const char *const *env, const char *name, ...)
 {
 	va_list args;
@@ -1807,3 +1918,21 @@ int run_processes_parallel(int n,
 	pp_cleanup(&pp);
 	return 0;
 }
+
+int run_processes_parallel_tr2(int n, get_next_task_fn get_next_task,
+			       start_failure_fn start_failure,
+			       task_finished_fn task_finished, void *pp_cb,
+			       const char *tr2_category, const char *tr2_label)
+{
+	int result;
+
+	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d",
+				   ((n < 1) ? online_cpus() : n));
+
+	result = run_processes_parallel(n, get_next_task, start_failure,
+					task_finished, pp_cb);
+
+	trace2_region_leave(tr2_category, tr2_label, NULL);
+
+	return result;
+}
diff --git a/run-command.h b/run-command.h
index 68f5369fc2d432..1886b21a9d9ad1 100644
--- a/run-command.h
+++ b/run-command.h
@@ -10,6 +10,12 @@ struct child_process {
 	struct argv_array args;
 	struct argv_array env_array;
 	pid_t pid;
+
+	int trace2_child_id;
+	uint64_t trace2_child_us_start;
+	const char *trace2_child_class;
+	const char *trace2_hook_name;
+
 	/*
 	 * Using .in, .out, .err:
 	 * - Specify 0 for no redirections (child inherits stdin, stdout,
@@ -65,6 +71,8 @@ extern const char *find_hook(const char *name);
 LAST_ARG_MUST_BE_NULL
 extern int run_hook_le(const char *const *env, const char *name, ...);
 extern int run_hook_ve(const char *const *env, const char *name, va_list args);
+extern int run_hook_argv(const char *const *env, const char *name,
+			 const char **argv);
 
 #define RUN_COMMAND_NO_STDIN 1
 #define RUN_GIT_CMD	     2	/*If this is to be git sub-command */
@@ -73,12 +81,14 @@ extern int run_hook_ve(const char *const *env, const char *name, va_list args);
 #define RUN_USING_SHELL 16
 #define RUN_CLEAN_ON_EXIT 32
 int run_command_v_opt(const char **argv, int opt);
-
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class);
 /*
  * env (the environment) is to be formatted like environ: "VAR=VALUE".
  * To unset an environment variable use just "VAR".
  */
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir,
+				 const char *const *env, const char *tr2_class);
 
 /**
  * Execute the given command, sending "in" to its stdin, and capturing its
@@ -220,5 +230,8 @@ int run_processes_parallel(int n,
 			   start_failure_fn,
 			   task_finished_fn,
 			   void *pp_cb);
+int run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
+			       task_finished_fn, void *pp_cb,
+			       const char *tr2_category, const char *tr2_label);
 
 #endif
diff --git a/send-pack.c b/send-pack.c
index fa9e8cf1fc0e83..a283e8e6230591 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -15,6 +15,7 @@
 #include "sha1-array.h"
 #include "gpg-interface.h"
 #include "cache.h"
+#include "gvfs.h"
 
 int option_parse_push_signed(const struct option *opt,
 			     const char *arg, int unset)
@@ -50,7 +51,7 @@ static int send_pack_config(const char *var, const char *value, void *unused)
 
 static void feed_object(const struct object_id *oid, FILE *fh, int negative)
 {
-	if (negative && !has_object_file(oid))
+	if (negative && !gvfs_config_is_set(GVFS_MISSING_OK) && !has_object_file(oid))
 		return;
 
 	if (negative)
diff --git a/sequencer.c b/sequencer.c
index 291a8ba0d2f360..96caac89bb3eab 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1103,6 +1103,7 @@ static int run_rewrite_hook(const struct object_id *oldoid,
 	proc.argv = argv;
 	proc.in = -1;
 	proc.stdout_to_stderr = 1;
+	proc.trace2_hook_name = "post-rewrite";
 
 	code = start_command(&proc);
 	if (code)
@@ -3786,6 +3787,7 @@ static int pick_commits(struct repository *r,
 				hook.in = open(rebase_path_rewritten_list(),
 					O_RDONLY);
 				hook.stdout_to_stderr = 1;
+				hook.trace2_hook_name = "post-rewrite";
 				argv_array_push(&hook.args, post_rewrite_hook);
 				argv_array_push(&hook.args, "rebase");
 				/* we don't care if this hook failed */
diff --git a/sh-i18n--envsubst.c b/sh-i18n--envsubst.c
index 09c6b445b96312..cecfdd36c7e696 100644
--- a/sh-i18n--envsubst.c
+++ b/sh-i18n--envsubst.c
@@ -14,6 +14,7 @@
  */
 
 #include "git-compat-util.h"
+#include "trace2.h"
 
 /* Substitution of environment variables in shell format strings.
    Copyright (C) 2003-2007 Free Software Foundation, Inc.
@@ -67,6 +68,8 @@ cmd_main (int argc, const char *argv[])
   /* Default values for command line options.  */
   /* unsigned short int show_variables = 0; */
 
+  trace2_cmd_name("sh-i18n--envsubst");
+
   switch (argc)
 	{
 	case 1:
diff --git a/sha1-file.c b/sha1-file.c
index 494606f7716923..0d05f75aa0f2fd 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -32,6 +32,9 @@
 #include "packfile.h"
 #include "fetch-object.h"
 #include "object-store.h"
+#include "sigchain.h"
+#include "sub-process.h"
+#include "pkt-line.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -760,6 +763,124 @@ void prepare_alt_odb(struct repository *r)
 	r->objects->loaded_alternates = 1;
 }
 
+#define CAP_GET    (1u<<0)
+
+static int subprocess_map_initialized;
+static struct hashmap subprocess_map;
+
+struct read_object_process {
+	struct subprocess_entry subprocess;
+	unsigned int supported_capabilities;
+};
+
+static int start_read_object_fn(struct subprocess_entry *subprocess)
+{
+	struct read_object_process *entry = (struct read_object_process *)subprocess;
+	static int versions[] = {1, 0};
+	static struct subprocess_capability capabilities[] = {
+		{ "get", CAP_GET },
+		{ NULL, 0 }
+	};
+
+	return subprocess_handshake(subprocess, "git-read-object", versions,
+				    NULL, capabilities,
+				    &entry->supported_capabilities);
+}
+
+static int read_object_process(const struct object_id *oid)
+{
+	int err;
+	struct read_object_process *entry;
+	struct child_process *process;
+	struct strbuf status = STRBUF_INIT;
+	const char *cmd = find_hook("read-object");
+	uint64_t start;
+
+	start = getnanotime();
+
+	trace2_region_enter("subprocess", "read_object", the_repository);
+
+	if (!subprocess_map_initialized) {
+		subprocess_map_initialized = 1;
+		hashmap_init(&subprocess_map, (hashmap_cmp_fn)cmd2process_cmp,
+			     NULL, 0);
+		entry = NULL;
+	} else {
+		entry = (struct read_object_process *) subprocess_find_entry(&subprocess_map, cmd);
+	}
+
+	if (!entry) {
+		entry = xmalloc(sizeof(*entry));
+		entry->supported_capabilities = 0;
+
+		if (subprocess_start(&subprocess_map, &entry->subprocess, cmd,
+				     start_read_object_fn)) {
+			free(entry);
+			err = -1;
+			goto leave_region;
+		}
+	}
+	process = &entry->subprocess.process;
+
+	if (!(CAP_GET & entry->supported_capabilities)) {
+		err = -1;
+		goto leave_region;
+	}
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	err = packet_write_fmt_gently(process->in, "command=get\n");
+	if (err)
+		goto done;
+
+	err = packet_write_fmt_gently(process->in, "sha1=%s\n", oid_to_hex(oid));
+	if (err)
+		goto done;
+
+	err = packet_flush_gently(process->in);
+	if (err)
+		goto done;
+
+	err = subprocess_read_status(process->out, &status);
+	err = err ? err : strcmp(status.buf, "success");
+
+done:
+	sigchain_pop(SIGPIPE);
+
+	if (err || errno == EPIPE) {
+		err = err ? err : errno;
+		if (!strcmp(status.buf, "error")) {
+			/* The process signaled a problem with the file. */
+		}
+		else if (!strcmp(status.buf, "abort")) {
+			/*
+			 * The process signaled a permanent problem. Don't try to read
+			 * objects with the same command for the lifetime of the current
+			 * Git process.
+			 */
+			entry->supported_capabilities &= ~CAP_GET;
+		}
+		else {
+			/*
+			 * Something went wrong with the read-object process.
+			 * Force shutdown and restart if needed.
+			 */
+			error("external process '%s' failed", cmd);
+			subprocess_stop(&subprocess_map,
+					(struct subprocess_entry *)entry);
+			free(entry);
+		}
+	}
+
+	trace_performance_since(start, "read_object_process");
+
+leave_region:
+	trace2_region_leave_printf("subprocess", "read_object", the_repository,
+				   "result %d", err);
+
+	return err;
+}
+
 /* Returns 1 if we have successfully freshened the file, 0 otherwise. */
 static int freshen_file(const char *fn)
 {
@@ -810,10 +931,23 @@ static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
 	return 0;
 }
 
-static int check_and_freshen(const struct object_id *oid, int freshen)
+static int check_and_freshen(const struct object_id *oid, int freshen,
+			     int skip_virtualized_objects)
 {
-	return check_and_freshen_local(oid, freshen) ||
+	int ret;
+	int tried_hook = 0;
+
+retry:
+	ret = check_and_freshen_local(oid, freshen) ||
 	       check_and_freshen_nonlocal(oid, freshen);
+	if (!ret && core_virtualize_objects && !skip_virtualized_objects &&
+	    !tried_hook) {
+		tried_hook = 1;
+		if (!read_object_process(oid))
+			goto retry;
+	}
+
+	return ret;
 }
 
 int has_loose_object_nonlocal(const struct object_id *oid)
@@ -823,7 +957,7 @@ int has_loose_object_nonlocal(const struct object_id *oid)
 
 static int has_loose_object(const struct object_id *oid)
 {
-	return check_and_freshen(oid, 0);
+	return check_and_freshen(oid, 0, 0);
 }
 
 static void mmap_limit_check(size_t length)
@@ -1320,6 +1454,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	int rtype;
 	const struct object_id *real = oid;
 	int already_retried = 0;
+	int tried_hook = 0;
 
 	if (flags & OBJECT_INFO_LOOKUP_REPLACE)
 		real = lookup_replace_object(r, oid);
@@ -1330,6 +1465,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	if (!oi)
 		oi = &blank_oi;
 
+retry:
 	if (!(flags & OBJECT_INFO_SKIP_CACHED)) {
 		struct cached_object *co = find_cached_object(real);
 		if (co) {
@@ -1366,6 +1502,11 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 			reprepare_packed_git(r);
 			if (find_pack_entry(r, real, &e))
 				break;
+			if (core_virtualize_objects && !tried_hook) {
+				tried_hook = 1;
+				if (!read_object_process(oid))
+					goto retry;
+			}
 		}
 
 		/* Check if it is a missing object */
@@ -1746,9 +1887,10 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 	return finalize_object_file(tmp_file.buf, filename.buf);
 }
 
-static int freshen_loose_object(const struct object_id *oid)
+static int freshen_loose_object(const struct object_id *oid,
+				int skip_virtualized_objects)
 {
-	return check_and_freshen(oid, 1);
+	return check_and_freshen(oid, 1, skip_virtualized_objects);
 }
 
 static int freshen_packed_object(const struct object_id *oid)
@@ -1774,7 +1916,7 @@ int write_object_file(const void *buf, unsigned long len, const char *type,
 	 * it out into .git/objects/??/?{38} file.
 	 */
 	write_object_file_prepare(buf, len, type, oid, hdr, &hdrlen);
-	if (freshen_packed_object(oid) || freshen_loose_object(oid))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
 		return 0;
 	return write_loose_object(oid, hdr, hdrlen, buf, len, 0);
 }
@@ -1793,7 +1935,7 @@ int hash_object_file_literally(const void *buf, unsigned long len,
 
 	if (!(flags & HASH_WRITE_OBJECT))
 		goto cleanup;
-	if (freshen_packed_object(oid) || freshen_loose_object(oid))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
 		goto cleanup;
 	status = write_loose_object(oid, header, hdrlen, buf, len, 0);
 
diff --git a/sha1-name.c b/sha1-name.c
index 375fba94a1ec46..0fe715b51ef3d4 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -1193,7 +1193,8 @@ static int get_oid_oneline(const char *prefix, struct object_id *oid,
 		struct commit *commit;
 		int matches;
 
-		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
+		commit = pop_most_recent_commit(&list, ONELINE_SEEN,
+						GENERATION_NUMBER_ZERO);
 		if (!parse_object(the_repository, &commit->object.oid))
 			continue;
 		buf = get_commit_buffer(commit, NULL);
diff --git a/sub-process.c b/sub-process.c
index 8d2a1707cfe1a7..3f4af935557c5e 100644
--- a/sub-process.c
+++ b/sub-process.c
@@ -88,6 +88,7 @@ int subprocess_start(struct hashmap *hashmap, struct subprocess_entry *entry, co
 	process->out = -1;
 	process->clean_on_exit = 1;
 	process->clean_on_exit_handler = subprocess_exit_handler;
+	process->trace2_child_class = "subprocess";
 
 	err = start_command(process);
 	if (err) {
diff --git a/submodule.c b/submodule.c
index 934ecfa2943bcb..174003a847aa9a 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1609,11 +1609,12 @@ int fetch_populated_submodules(struct repository *r,
 
 	calculate_changed_submodule_paths(r, &spf.changed_submodule_names);
 	string_list_sort(&spf.changed_submodule_names);
-	run_processes_parallel(max_parallel_jobs,
-			       get_next_submodule,
-			       fetch_start_failure,
-			       fetch_finish,
-			       &spf);
+	run_processes_parallel_tr2(max_parallel_jobs,
+				   get_next_submodule,
+				   fetch_start_failure,
+				   fetch_finish,
+				   &spf,
+				   "submodule", "parallel/fetch");
 
 	argv_array_clear(&spf.args);
 out:
diff --git a/t/helper/test-parse-options.c b/t/helper/test-parse-options.c
index 47fee660b86a6e..cc88fba05752cb 100644
--- a/t/helper/test-parse-options.c
+++ b/t/helper/test-parse-options.c
@@ -2,6 +2,7 @@
 #include "cache.h"
 #include "parse-options.h"
 #include "string-list.h"
+#include "trace2.h"
 
 static int boolean = 0;
 static int integer = 0;
@@ -153,6 +154,8 @@ int cmd__parse_options(int argc, const char **argv)
 	int i;
 	int ret = 0;
 
+	trace2_cmd_name("_parse_");
+
 	argc = parse_options(argc, (const char **)argv, prefix, options, usage, 0);
 
 	if (length_cb.called) {
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 716e8f679a4a20..9445204e6ec92e 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -1,5 +1,6 @@
 #include "git-compat-util.h"
 #include "test-tool.h"
+#include "trace2.h"
 
 struct test_cmd {
 	const char *name;
@@ -53,6 +54,7 @@ static struct test_cmd cmds[] = {
 	{ "submodule-config", cmd__submodule_config },
 	{ "submodule-nested-repo-config", cmd__submodule_nested_repo_config },
 	{ "subprocess", cmd__subprocess },
+	{ "trace2", cmd__trace2 },
 	{ "urlmatch-normalization", cmd__urlmatch_normalization },
 	{ "xml-encode", cmd__xml_encode },
 	{ "wildmatch", cmd__wildmatch },
@@ -84,6 +86,8 @@ int cmd_main(int argc, const char **argv)
 		if (!strcmp(cmds[i].name, argv[1])) {
 			argv++;
 			argc--;
+			trace2_cmd_name(cmds[i].name);
+			trace2_cmd_list_config();
 			return cmds[i].fn(argc, argv);
 		}
 	}
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index f75e948a94673d..24126ff96e42e4 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -50,6 +50,7 @@ int cmd__string_list(int argc, const char **argv);
 int cmd__submodule_config(int argc, const char **argv);
 int cmd__submodule_nested_repo_config(int argc, const char **argv);
 int cmd__subprocess(int argc, const char **argv);
+int cmd__trace2(int argc, const char **argv);
 int cmd__urlmatch_normalization(int argc, const char **argv);
 int cmd__xml_encode(int argc, const char **argv);
 int cmd__wildmatch(int argc, const char **argv);
diff --git a/t/helper/test-trace2.c b/t/helper/test-trace2.c
new file mode 100644
index 00000000000000..197819c872eec7
--- /dev/null
+++ b/t/helper/test-trace2.c
@@ -0,0 +1,273 @@
+#include "test-tool.h"
+#include "cache.h"
+#include "argv-array.h"
+#include "run-command.h"
+#include "exec-cmd.h"
+#include "config.h"
+
+typedef int(fn_unit_test)(int argc, const char **argv);
+
+struct unit_test {
+	fn_unit_test *ut_fn;
+	const char *ut_name;
+	const char *ut_usage;
+};
+
+#define MyOk 0
+#define MyError 1
+
+static int get_i(int *p_value, const char *data)
+{
+	char *endptr;
+
+	if (!data || !*data)
+		return MyError;
+
+	*p_value = strtol(data, &endptr, 10);
+	if (*endptr || errno == ERANGE)
+		return MyError;
+
+	return MyOk;
+}
+
+/*
+ * Cause process to exit with the requested value via "return".
+ *
+ * Rely on test-tool.c:cmd_main() to call trace2_cmd_exit()
+ * with our result.
+ *
+ * Test harness can confirm:
+ * [] the process-exit value.
+ * [] the "code" field in the "exit" trace2 event.
+ * [] the "code" field in the "atexit" trace2 event.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] "def_param" events for all of the "interesting" pre-defined
+ * config settings.
+ */
+static int ut_001return(int argc, const char **argv)
+{
+	int rc;
+
+	if (get_i(&rc, argv[0]))
+		die("expect <exit_code>");
+
+	return rc;
+}
+
+/*
+ * Cause the process to exit with the requested value via "exit()".
+ *
+ * Test harness can confirm:
+ * [] the "code" field in the "exit" trace2 event.
+ * [] the "code" field in the "atexit" trace2 event.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] "def_param" events for all of the "interesting" pre-defined
+ * config settings.
+ */
+static int ut_002exit(int argc, const char **argv)
+{
+	int rc;
+
+	if (get_i(&rc, argv[0]))
+		die("expect <exit_code>");
+
+	exit(rc);
+}
+
+/*
+ * Send an "error" event with each value in argv.  Normally, git only issues
+ * a single "error" event immediately before issuing an "exit" event (such
+ * as in die() or BUG()), but multiple "error" events are allowed.
+ *
+ * Test harness can confirm:
+ * [] a trace2 "error" event for each value in argv.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] (optional) the file:line in the "exit" event refers to this function.
+ */
+static int ut_003error(int argc, const char **argv)
+{
+	int k;
+
+	if (!argv[0] || !*argv[0])
+		die("expect <error_message>");
+
+	for (k = 0; k < argc; k++)
+		error("%s", argv[k]);
+
+	return 0;
+}
+
+/*
+ * Run a child process and wait for it to finish and exit with its return code.
+ * test-tool trace2 004child [<child-command-line>]
+ *
+ * For example:
+ * test-tool trace2 004child git version
+ * test-tool trace2 004child test-tool trace2 001return 0
+ * test-tool trace2 004child test-tool trace2 004child test-tool trace2 004child
+ * test-tool trace2 004child git -c alias.xyz=version xyz
+ *
+ * Test harness can confirm:
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] that the outer process has a single component SID (or depth "d0" in
+ *    the PERF stream).
+ * [] that "child_start" and "child_exit" events are generated for the child.
+ * [] if the child process is an instrumented executable:
+ *    [] that "version", "start", ..., "exit", and "atexit" events are
+ *       generated by the child process.
+ *    [] that the child process events have a multiple component SID (or
+ *       depth "dN+1" in the PERF stream).
+ * [] that the child exit code is propagated to the parent process "exit"
+ *    and "atexit" events..
+ * [] (optional) that the "t_abs" field in the child process "atexit" event
+ *    is less than the "t_rel" field in the "child_exit" event of the parent
+ *    process.
+ * [] if the child process is like the alias example above,
+ *    [] (optional) the child process attempts to run "git-xyx" as a dashed
+ *       command.
+ *    [] the child process emits an "alias" event with "xyz" => "version"
+ *    [] the child process runs "git version" as a child process.
+ *    [] the child process has a 3 component SID (or depth "d2" in the PERF
+ *       stream).
+ */
+static int ut_004child(int argc, const char **argv)
+{
+	int result;
+
+	/*
+	 * Allow empty <child_command_line> so we can do arbitrarily deep
+	 * command nesting and let the last one be null.
+	 */
+	if (!argc)
+		return 0;
+
+	result = run_command_v_opt(argv, 0);
+	exit(result);
+}
+
+/*
+ * Exec a git command.  This may either create a child process (Windows)
+ * or replace the existing process.
+ * test-tool trace2 005exec <git_command_args>
+ *
+ * For example:
+ * test-tool trace2 005exec version
+ *
+ * Test harness can confirm (on Windows):
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] that the outer process has a single component SID (or depth "d0" in
+ *    the PERF stream).
+ * [] that "exec" and "exec_result" events are generated for the child
+ *    process (since the Windows compatibility layer fakes an exec() with
+ *    a CreateProcess(), WaitForSingleObject(), and exit()).
+ * [] that the child process has multiple component SID (or depth "dN+1"
+ *    in the PERF stream).
+ *
+ * Test harness can confirm (on platforms with a real exec() function):
+ * [] TODO talk about process replacement and how it affects SID.
+ */
+static int ut_005exec(int argc, const char **argv)
+{
+	int result;
+
+	if (!argc)
+		return 0;
+
+	result = execv_git_cmd(argv);
+	return result;
+}
+
+static int ut_006data(int argc, const char **argv)
+{
+	const char *usage_error =
+		"expect <cat0> <k0> <v0> [<cat1> <k1> <v1> [...]]";
+
+	if (argc % 3 != 0)
+		die("%s", usage_error);
+
+	while (argc) {
+		if (!argv[0] || !*argv[0] || !argv[1] || !*argv[1] ||
+		    !argv[2] || !*argv[2])
+			die("%s", usage_error);
+
+		trace2_data_string(argv[0], the_repository, argv[1], argv[2]);
+		argv += 3;
+		argc -= 3;
+	}
+
+	return 0;
+}
+
+/*
+ * Usage:
+ *     test-tool trace2 <ut_name_1> <ut_usage_1>
+ *     test-tool trace2 <ut_name_2> <ut_usage_2>
+ *     ...
+ */
+#define USAGE_PREFIX "test-tool trace2"
+
+/* clang-format off */
+static struct unit_test ut_table[] = {
+	{ ut_001return,   "001return", "<exit_code>" },
+	{ ut_002exit,     "002exit",   "<exit_code>" },
+	{ ut_003error,    "003error",  "<error_message>+" },
+	{ ut_004child,    "004child",  "[<child_command_line>]" },
+	{ ut_005exec,     "005exec",   "<git_command_args>" },
+	{ ut_006data,     "006data",   "[<category> <key> <value>]+" },
+};
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_ut(k, ut_k)			\
+	for (k = 0, ut_k = &ut_table[k];	\
+	     k < ARRAY_SIZE(ut_table);		\
+	     k++, ut_k = &ut_table[k])
+/* clang-format on */
+
+static int print_usage(void)
+{
+	int k;
+	struct unit_test *ut_k;
+
+	fprintf(stderr, "usage:\n");
+	for_each_ut (k, ut_k)
+		fprintf(stderr, "\t%s %s %s\n", USAGE_PREFIX, ut_k->ut_name,
+			ut_k->ut_usage);
+
+	return 129;
+}
+
+/*
+ * Issue various trace2 events for testing.
+ *
+ * We assume that these trace2 routines has already been called:
+ *    [] trace2_initialize()      [common-main.c:main()]
+ *    [] trace2_cmd_start()       [common-main.c:main()]
+ *    [] trace2_cmd_name()        [test-tool.c:cmd_main()]
+ *    [] tracd2_cmd_list_config() [test-tool.c:cmd_main()]
+ * So that:
+ *    [] the various trace2 streams are open.
+ *    [] the process SID has been created.
+ *    [] the "version" event has been generated.
+ *    [] the "start" event has been generated.
+ *    [] the "cmd_name" event has been generated.
+ *    [] this writes various "def_param" events for interesting config values.
+ *
+ * We further assume that if we return (rather than exit()), trace2_cmd_exit()
+ * will be called by test-tool.c:cmd_main().
+ */
+int cmd__trace2(int argc, const char **argv)
+{
+	int k;
+	struct unit_test *ut_k;
+
+	argc--; /* skip over "trace2" arg */
+	argv++;
+
+	if (argc)
+		for_each_ut (k, ut_k)
+			if (!strcmp(argv[0], ut_k->ut_name))
+				return ut_k->ut_fn(argc - 1, argv + 1);
+
+	return print_usage();
+}
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index b6566003dd8704..c5e6ec3f3c7e96 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -1079,6 +1079,11 @@ test_expect_success 'writing this tree with --missing-ok' '
 	git write-tree --missing-ok
 '
 
+test_expect_success 'writing this tree with missing ok config value' '
+	git config core.gvfs 4 &&
+	git write-tree
+'
+
 
 ################################################################
 test_expect_success 'git read-tree followed by write-tree should be idempotent' '
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index a6c5fe9e1475ae..d13aa011e00431 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -93,6 +93,7 @@ test_expect_success 'No extra GIT_* on alias scripts' '
 		sed -n \
 			-e "/^GIT_PREFIX=/d" \
 			-e "/^GIT_TEXTDOMAINDIR=/d" \
+			-e "/^GIT_TR2_PARENT/d" \
 			-e "/^GIT_/s/=.*//p" |
 		sort
 	EOF
diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index 27c3d0afb29106..1a95d4a73dcf82 100755
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -314,6 +314,43 @@ test_expect_success "filter: smudge empty file" '
 	test_cmp expected filtered-empty-in-repo
 '
 
+test_expect_success "filter: clean filters blocked when under GVFS" '
+	test_config filter.empty-in-repo.clean "cat >/dev/null" &&
+	test_config filter.empty-in-repo.smudge "echo smudged && cat" &&
+	test_config core.gvfs 64 &&
+
+	echo dead data walking >empty-in-repo &&
+	test_must_fail git add empty-in-repo
+'
+
+test_expect_success "filter: smudge filters blocked when under GVFS" '
+	test_config filter.empty-in-repo.clean "cat >/dev/null" &&
+	test_config filter.empty-in-repo.smudge "echo smudged && cat" &&
+	test_config core.gvfs 64 &&
+
+	test_must_fail git checkout
+'
+
+test_expect_success "ident blocked on add when under GVFS" '
+	test_config core.gvfs 64 &&
+	test_config core.autocrlf false &&
+
+	echo "*.i ident" >.gitattributes &&
+	echo "\$Id\$" > ident.i &&
+
+	test_must_fail git add ident.i
+'
+
+test_expect_success "ident blocked when under GVFS" '
+	git add ident.i &&
+
+	git commit -m "added ident.i" &&
+	test_config core.gvfs 64 &&
+	rm ident.i &&
+
+	test_must_fail git checkout -- ident.i
+'
+
 test_expect_success 'disable filter with empty override' '
 	test_config_global filter.disable.smudge false &&
 	test_config_global filter.disable.clean false &&
diff --git a/t/t0027-auto-crlf.sh b/t/t0027-auto-crlf.sh
index 3587e454f19d9b..8abb4bdfbd7ead 100755
--- a/t/t0027-auto-crlf.sh
+++ b/t/t0027-auto-crlf.sh
@@ -331,6 +331,18 @@ checkout_files () {
 	"
 }
 
+test_expect_success 'crlf conversions blocked when under GVFS' '
+	git checkout -b gvfs &&
+	test_commit initial &&
+	rm initial.t &&
+	test_config core.gvfs 64 &&
+	test_config core.autocrlf true &&
+	test_must_fail git read-tree --reset -u HEAD &&
+
+	git config core.autocrlf false &&
+	git read-tree --reset -u HEAD
+'
+
 # Test control characters
 # NUL SOH CR EOF==^Z
 test_expect_success 'ls-files --eol -o Text/Binary' '
diff --git a/t/t0210-trace2-normal.sh b/t/t0210-trace2-normal.sh
new file mode 100755
index 00000000000000..8d17e1e6f15120
--- /dev/null
+++ b/t/t0210-trace2-normal.sh
@@ -0,0 +1,174 @@
+#!/bin/sh
+
+test_description='test trace2 facility (normal target)'
+. ./test-lib.sh
+
+# Turn off any inherited trace2 settings for this test.
+sane_unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+sane_unset GIT_TR2_BRIEF
+sane_unset GIT_TR2_CONFIG_PARAMS
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# This script tests the normal target in isolation.
+#
+# Defer setting GIT_TR2 until the actual command line we want to test
+# because hidden git and test-tool commands run by the test harness
+# can contaminate our output.
+
+# Enable "brief" feature which turns off "<clock> <file>:<line> " prefix.
+GIT_TR2_BRIEF=1 && export GIT_TR2_BRIEF
+
+# Basic tests of the trace2 normal stream.  Since this stream is used
+# primarily with printf-style debugging/tracing, we do limited testing
+# here.
+#
+# We do confirm the following API features:
+# [] the 'version <v>' event
+# [] the 'start <argv>' event
+# [] the 'cmd_name <name>' event
+# [] the 'exit <time> code:<code>' event
+# [] the 'atexit <time> code:<code>' event
+#
+# Fields of the form _FIELD_ are tokens that have been replaced (such
+# as the elapsed time).
+
+# Verb 001return
+#
+# Implicit return from cmd_<verb> function propagates <code>.
+
+test_expect_success 'normal stream, return code 0' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'normal stream, return code 1' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_must_fail env GIT_TR2="$(pwd)/trace.normal" test-tool trace2 001return 1 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 1
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:1
+		atexit elapsed:_TIME_ code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 002exit
+#
+# Explicit exit(code) from within cmd_<verb> propagates <code>.
+
+test_expect_success 'normal stream, exit code 0' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 002exit 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 002exit 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'normal stream, exit code 1' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_must_fail env GIT_TR2="$(pwd)/trace.normal" test-tool trace2 002exit 1 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 002exit 1
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:1
+		atexit elapsed:_TIME_ code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success 'normal stream, error event' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 003error '\''hello world'\'' '\''this is a test'\''
+		cmd_name trace2 (trace2)
+		error hello world
+		error this is a test
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+sane_unset GIT_TR2_BRIEF
+
+# Now test without environment variables and get all Trace2 settings
+# from the global config.
+
+test_expect_success 'using global config, normal stream, return code 0' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_config_global trace2.normalBrief 1 &&
+	test_config_global trace2.normalTarget "$(pwd)/trace.normal" &&
+	test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'using global config with include' '
+	test_when_finished "rm trace.normal actual expect real.gitconfig" &&
+	test_config_global trace2.normalBrief 1 &&
+	test_config_global trace2.normalTarget "$(pwd)/trace.normal" &&
+	mv "$(pwd)/.gitconfig" "$(pwd)/real.gitconfig" &&
+	test_config_global include.path "$(pwd)/real.gitconfig" &&
+	test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_done
diff --git a/t/t0210/scrub_normal.perl b/t/t0210/scrub_normal.perl
new file mode 100644
index 00000000000000..c65d1a815ea3d8
--- /dev/null
+++ b/t/t0210/scrub_normal.perl
@@ -0,0 +1,48 @@
+#!/usr/bin/perl
+#
+# Scrub the variable fields from the normal trace2 output to
+# make testing easier.
+
+use strict;
+use warnings;
+
+my $float = '[0-9]*\.[0-9]+([eE][-+]?[0-9]+)?';
+
+# This code assumes that the trace2 data was written with bare
+# turned on (which omits the "<clock> <file>:<line>" prefix.
+
+while (<>) {
+    # Various messages include an elapsed time in the middle
+    # of the message.  Replace the time with a placeholder to
+    # simplify our HEREDOC in the test script.
+    s/elapsed:$float/elapsed:_TIME_/g;
+
+    my $line = $_;
+
+    # we expect:
+    #    start <argv0> [<argv1> [<argv2> [...]]]
+    #
+    # where argv0 might be a relative or absolute path, with
+    # or without quotes, and platform dependent.  Replace argv0
+    # with a token for HEREDOC matching in the test script.
+
+    if ($line =~ m/^start/) {
+	$line =~ /^start\s+(.*)/;
+	my $argv = $1;
+	$argv =~ m/(\'[^\']*\'|[^ ]+)\s+(.*)/;
+	my $argv_0 = $1;
+	my $argv_rest = $2;
+
+	print "start _EXE_ $argv_rest\n";
+    }
+    elsif ($line =~ m/^cmd_path/) {
+	# Likewise, the 'cmd_path' message breaks out argv[0].
+	#
+	# This line is only emitted when RUNTIME_PREFIX is defined,
+	# so just omit it for testing purposes.
+	# print "cmd_path _EXE_\n";
+    }
+    else {
+	print "$line";
+    }
+}
diff --git a/t/t0211-trace2-perf.sh b/t/t0211-trace2-perf.sh
new file mode 100755
index 00000000000000..b501e867af5404
--- /dev/null
+++ b/t/t0211-trace2-perf.sh
@@ -0,0 +1,174 @@
+#!/bin/sh
+
+test_description='test trace2 facility (perf target)'
+. ./test-lib.sh
+
+# Turn off any inherited trace2 settings for this test.
+sane_unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+sane_unset GIT_TR2_PERF_BRIEF
+sane_unset GIT_TR2_CONFIG_PARAMS
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# Test each target independently.
+#
+# Defer setting GIT_TR2_PERF until the actual command we want to
+# test because hidden git and test-tool commands in the test
+# harness can contaminate our output.
+
+# Enable "brief" feature which turns off the prefix:
+#     "<clock> <file>:<line> | <nr_parents> | "
+GIT_TR2_PERF_BRIEF=1 && export GIT_TR2_PERF_BRIEF
+
+# Repeat some of the t0210 tests using the perf target stream instead of
+# the normal stream.
+#
+# Tokens here of the form _FIELD_ have been replaced in the observed output.
+
+# Verb 001return
+#
+# Implicit return from cmd_<verb> function propagates <code>.
+
+test_expect_success 'perf stream, return code 0' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start||_T_ABS_|||_EXE_ trace2 001return 0
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'perf stream, return code 1' '
+	test_when_finished "rm trace.perf actual expect" &&
+	test_must_fail env GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 001return 1 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start||_T_ABS_|||_EXE_ trace2 001return 1
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|exit||_T_ABS_|||code:1
+		d0|main|atexit||_T_ABS_|||code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success 'perf stream, error event' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start||_T_ABS_|||_EXE_ trace2 003error '\''hello world'\'' '\''this is a test'\''
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|error|||||hello world
+		d0|main|error|||||this is a test
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 004child
+#
+# Test nested spawning of child processes.
+#
+# Conceptually, this looks like:
+#    P1: TT trace2 004child
+#    P2: |--- TT trace2 004child
+#    P3:      |--- TT trace2 001return 0
+#
+# Which should generate events:
+#    P1: version
+#    P1: start
+#    P1: cmd_name
+#    P1: child_start
+#        P2: version
+#        P2: start
+#        P2: cmd_name
+#        P2: child_start
+#            P3: version
+#            P3: start
+#            P3: cmd_name
+#            P3: exit
+#            P3: atexit
+#        P2: child_exit
+#        P2: exit
+#        P2: atexit
+#    P1: child_exit
+#    P1: exit
+#    P1: atexit
+
+test_expect_success 'perf stream, child processes' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 004child test-tool trace2 004child test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start||_T_ABS_|||_EXE_ trace2 004child test-tool trace2 004child test-tool trace2 001return 0
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 004child test-tool trace2 001return 0
+		d1|main|version|||||$V
+		d1|main|start||_T_ABS_|||_EXE_ trace2 004child test-tool trace2 001return 0
+		d1|main|cmd_name|||||trace2 (trace2/trace2)
+		d1|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 001return 0
+		d2|main|version|||||$V
+		d2|main|start||_T_ABS_|||_EXE_ trace2 001return 0
+		d2|main|cmd_name|||||trace2 (trace2/trace2/trace2)
+		d2|main|exit||_T_ABS_|||code:0
+		d2|main|atexit||_T_ABS_|||code:0
+		d1|main|child_exit||_T_ABS_|_T_REL_||[ch0] pid:_PID_ code:0
+		d1|main|exit||_T_ABS_|||code:0
+		d1|main|atexit||_T_ABS_|||code:0
+		d0|main|child_exit||_T_ABS_|_T_REL_||[ch0] pid:_PID_ code:0
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+sane_unset GIT_TR2_PERF_BRIEF
+
+# Now test without environment variables and get all Trace2 settings
+# from the global config.
+
+test_expect_success 'using global config, perf stream, return code 0' '
+	test_when_finished "rm trace.perf actual expect" &&
+	test_config_global trace2.perfBrief 1 &&
+	test_config_global trace2.perfTarget "$(pwd)/trace.perf" &&
+	test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start||_T_ABS_|||_EXE_ trace2 001return 0
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_done
diff --git a/t/t0211/scrub_perf.perl b/t/t0211/scrub_perf.perl
new file mode 100644
index 00000000000000..351af7844ed95d
--- /dev/null
+++ b/t/t0211/scrub_perf.perl
@@ -0,0 +1,76 @@
+#!/usr/bin/perl
+#
+# Scrub the variable fields from the perf trace2 output to
+# make testing easier.
+
+use strict;
+use warnings;
+
+my $qpath = '\'[^\']*\'|[^ ]*';
+
+my $col_depth=0;
+my $col_thread=1;
+my $col_event=2;
+my $col_repo=3;
+my $col_t_abs=4;
+my $col_t_rel=5;
+my $col_category=6;
+my $col_rest=7;
+
+# This code assumes that the trace2 data was written with bare
+# turned on (which omits the "<clock> <file>:<line> | <parents>"
+# prefix.
+
+while (<>) {
+    my @tokens = split /\|/;
+
+    foreach my $col (@tokens) { $col =~ s/^\s+|\s+$//g; }
+
+    if ($tokens[$col_event] =~ m/^start/) {
+	# The 'start' message lists the contents of argv in $col_rest.
+	# On some platforms (Windows), argv[0] is *sometimes* a canonical
+	# absolute path to the EXE rather than the value passed in the
+	# shell script.  Replace it with a placeholder to simplify our
+	# HEREDOC in the test script.
+	my $argv0;
+	my $argvRest;
+	$tokens[$col_rest] =~ s/^($qpath)\W*(.*)/_EXE_ $2/;
+    }
+    elsif ($tokens[$col_event] =~ m/cmd_path/) {
+	# Likewise, the 'cmd_path' message breaks out argv[0].
+	#
+	# This line is only emitted when RUNTIME_PREFIX is defined,
+	# so just omit it for testing purposes.
+	# $tokens[$col_rest] = "_EXE_";
+	goto SKIP_LINE;
+    }
+    elsif ($tokens[$col_event] =~ m/child_exit/) {
+	$tokens[$col_rest] =~ s/ pid:\d* / pid:_PID_ /;
+    }
+    elsif ($tokens[$col_event] =~ m/data/) {
+	if ($tokens[$col_category] =~ m/process/) {
+	    # 'data' and 'data_json' events containing 'process'
+	    # category data are assumed to be platform-specific
+	    # and highly variable.  Just omit them.
+	    goto SKIP_LINE;
+	}
+    }
+
+    # t_abs and t_rel are either blank or a float.  Replace the float
+    # with a constant for matching the HEREDOC in the test script.
+    if ($tokens[$col_t_abs] =~ m/\d/) {
+	$tokens[$col_t_abs] = "_T_ABS_";
+    }
+    if ($tokens[$col_t_rel] =~ m/\d/) {
+	$tokens[$col_t_rel] = "_T_REL_";
+    }
+
+    my $out;
+
+    $out = join('|', @tokens);
+    print "$out\n";
+
+  SKIP_LINE:
+}
+
+
diff --git a/t/t0212-trace2-event.sh b/t/t0212-trace2-event.sh
new file mode 100755
index 00000000000000..59adae8123c964
--- /dev/null
+++ b/t/t0212-trace2-event.sh
@@ -0,0 +1,268 @@
+#!/bin/sh
+
+test_description='test trace2 facility'
+. ./test-lib.sh
+
+# Turn off any inherited trace2 settings for this test.
+sane_unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+sane_unset GIT_TR2_BARE
+sane_unset GIT_TR2_CONFIG_PARAMS
+
+perl -MJSON::PP -e 0 >/dev/null 2>&1 && test_set_prereq JSON_PP
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# Test each target independently.
+#
+# Defer setting GIT_TR2_PERF until the actual command we want to
+# test because hidden git and test-tool commands in the test
+# harness can contaminate our output.
+
+# We don't bother repeating the 001return and 002exit tests, since they
+# have coverage in the normal and perf targets.
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success JSON_PP 'event stream, error event' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "003error",
+	|      "hello world",
+	|      "this is a test"
+	|    ],
+	|    "errors":[
+	|      "%s",
+	|      "%s"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 004child
+#
+# Test nested spawning of child processes.
+#
+# Conceptually, this looks like:
+#    P1: TT trace2 004child
+#    P2: |--- TT trace2 004child
+#    P3:      |--- TT trace2 001return 0
+
+test_expect_success JSON_PP 'event stream, return code 0' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 004child test-tool trace2 004child test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "child":{
+	|      "0":{
+	|        "child_argv":[
+	|          "_EXE_",
+	|          "trace2",
+	|          "004child",
+	|          "test-tool",
+	|          "trace2",
+	|          "001return",
+	|          "0"
+	|        ],
+	|        "child_class":"?",
+	|        "child_code":0,
+	|        "use_shell":0
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  },
+	|  "_SID0_/_SID1_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "child":{
+	|      "0":{
+	|        "child_argv":[
+	|          "_EXE_",
+	|          "trace2",
+	|          "001return",
+	|          "0"
+	|        ],
+	|        "child_class":"?",
+	|        "child_code":0,
+	|        "use_shell":0
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2/trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  },
+	|  "_SID0_/_SID1_/_SID2_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2/trace2/trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+# Test listing of all "interesting" config settings.
+
+test_expect_success JSON_PP 'event stream, list config' '
+	test_when_finished "rm trace.event actual expect" &&
+	git config --local t0212.abc 1 &&
+	git config --local t0212.def "hello world" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" GIT_TR2_CONFIG_PARAMS="t0212.*" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "params":[
+	|      {
+	|        "param":"t0212.abc",
+	|        "value":"1"
+	|      },
+	|      {
+	|        "param":"t0212.def",
+	|        "value":"hello world"
+	|      }
+	|    ],
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success JSON_PP 'basic trace2_data' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 006data test_category k1 v1 test_category k2 v2 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "006data",
+	|      "test_category",
+	|      "k1",
+	|      "v1",
+	|      "test_category",
+	|      "k2",
+	|      "v2"
+	|    ],
+	|    "data":{
+	|      "test_category":{
+	|        "k1":"v1",
+	|        "k2":"v2"
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+# Now test without environment variables and get all Trace2 settings
+# from the global config.
+
+test_expect_success JSON_PP 'using global config, event stream, error event' '
+	test_when_finished "rm trace.event actual expect" &&
+	test_config_global trace2.eventTarget "$(pwd)/trace.event" &&
+	test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "003error",
+	|      "hello world",
+	|      "this is a test"
+	|    ],
+	|    "errors":[
+	|      "%s",
+	|      "%s"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+test_done
diff --git a/t/t0212/parse_events.perl b/t/t0212/parse_events.perl
new file mode 100644
index 00000000000000..a2776ba216781b
--- /dev/null
+++ b/t/t0212/parse_events.perl
@@ -0,0 +1,251 @@
+#!/usr/bin/perl
+#
+# Parse event stream and convert individual events into a summary
+# record for the process.
+#
+# Git.exe generates one or more "event" records for each API method,
+# such as "start <argv>" and "exit <code>", during the life of the git
+# process.  Additionally, the input may contain interleaved events
+# from multiple concurrent git processes and/or multiple threads from
+# within a git process.
+#
+# Accumulate events for each process (based on its unique SID) in a
+# dictionary and emit process summary records.
+#
+# Convert some of the variable fields (such as elapsed time) into
+# placeholders (or omit them) to make HEREDOC comparisons easier in
+# the test scripts.
+#
+# We may also omit fields not (currently) useful for testing purposes.
+
+use strict;
+use warnings;
+use JSON::PP;
+use Data::Dumper;
+use Getopt::Long;
+
+# The version of the trace2 event target format that we understand.
+# This is reported in the 'version' event in the 'evt' field.
+# It comes from the GIT_TR2_EVENT_VERSION macro in trace2/tr2_tgt_event.c
+my $evt_version = '1';
+
+my $show_children = 1;
+my $show_exec     = 1;
+my $show_threads  = 1;
+
+# A hack to generate test HEREDOC data for pasting into the test script.
+# Usage:
+#    cd "t/trash directory.t0212-trace2-event"
+#    $TT trace ... >trace.event
+#    VV=$(../../git.exe version | sed -e 's/^git version //')
+#    perl ../t0212/parse_events.perl --HEREDOC --VERSION=$VV <trace.event >heredoc
+# Then paste heredoc into your new test.
+
+my $gen_heredoc = 0;
+my $gen_version = '';
+
+GetOptions("children!" => \$show_children,
+	   "exec!"     => \$show_exec,
+	   "threads!"  => \$show_threads,
+	   "HEREDOC!"  => \$gen_heredoc,
+	   "VERSION=s" => \$gen_version    )
+    or die("Error in command line arguments\n");
+
+
+# SIDs contains timestamps and PIDs of the process and its parents.
+# This makes it difficult to match up in a HEREDOC in the test script.
+# Build a map from actual SIDs to predictable constant values and yet
+# keep the parent/child relationships.  For example:
+# {..., "sid":"1539706952458276-8652", ...}
+# {..., "sid":"1539706952458276-8652/1539706952649493-15452", ...}
+# becomes:
+# {..., "sid":"_SID1_", ...}
+# {..., "sid":"_SID1_/_SID2_", ...}
+my $sid_map;
+my $sid_count = 0;
+
+my $processes;
+
+while (<>) {
+    my $line = decode_json( $_ );
+
+    my $sid = "";
+    my $sid_sep = "";
+
+    my $raw_sid = $line->{'sid'};
+    my @raw_sid_parts = split /\//, $raw_sid;
+    foreach my $raw_sid_k (@raw_sid_parts) {
+	if (!exists $sid_map->{$raw_sid_k}) {
+	    $sid_map->{$raw_sid_k} = '_SID' . $sid_count . '_';
+	    $sid_count++;
+	}
+	$sid = $sid . $sid_sep . $sid_map->{$raw_sid_k};
+	$sid_sep = '/';
+    }
+    
+    my $event = $line->{'event'};
+
+    if ($event eq 'version') {
+	$processes->{$sid}->{'version'} = $line->{'exe'};
+	if ($gen_heredoc == 1 && $gen_version eq $line->{'exe'}) {
+	    # If we are generating data FOR the test script, replace
+	    # the reported git.exe version with a reference to an
+	    # environment variable.  When our output is pasted into
+	    # the test script, it will then be expanded in future
+	    # test runs to the THEN current version of git.exe.
+	    # We assume that the test script uses env var $V.
+	    $processes->{$sid}->{'version'} = "\$V";
+	}
+    }
+
+    elsif ($event eq 'start') {
+	$processes->{$sid}->{'argv'} = $line->{'argv'};
+	$processes->{$sid}->{'argv'}[0] = "_EXE_";
+    }
+
+    elsif ($event eq 'exit') {
+	$processes->{$sid}->{'exit_code'} = $line->{'code'};
+    }
+
+    elsif ($event eq 'atexit') {
+	$processes->{$sid}->{'exit_code'} = $line->{'code'};
+    }
+
+    elsif ($event eq 'error') {
+	# For HEREDOC purposes, use the error message format string if
+	# available, rather than the formatted message (which probably
+	# has an absolute pathname).
+	if (exists $line->{'fmt'}) {
+	    push( @{$processes->{$sid}->{'errors'}}, $line->{'fmt'} );
+	}
+	elsif (exists $line->{'msg'}) {
+	    push( @{$processes->{$sid}->{'errors'}}, $line->{'msg'} );
+	}
+    }
+
+    elsif ($event eq 'cmd_path') {
+	## $processes->{$sid}->{'path'} = $line->{'path'};
+	#
+	# Like in the 'start' event, we need to replace the value of
+	# argv[0] with a token for HEREDOC purposes.  However, the
+	# event is only emitted when RUNTIME_PREFIX is defined, so
+	# just omit it for testing purposes.
+	# $processes->{$sid}->{'path'} = "_EXE_";
+    }
+    
+    elsif ($event eq 'cmd_name') {
+	$processes->{$sid}->{'name'} = $line->{'name'};
+	$processes->{$sid}->{'hierarchy'} = $line->{'hierarchy'};
+    }
+
+    elsif ($event eq 'alias') {
+	$processes->{$sid}->{'alias'}->{'key'} = $line->{'alias'};
+	$processes->{$sid}->{'alias'}->{'argv'} = $line->{'argv'};
+    }
+
+    elsif ($event eq 'def_param') {
+	my $kv;
+	$kv->{'param'} = $line->{'param'};
+	$kv->{'value'} = $line->{'value'};
+	push( @{$processes->{$sid}->{'params'}}, $kv );
+    }
+
+    elsif ($event eq 'child_start') {
+	if ($show_children == 1) {
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_class'} = $line->{'child_class'};
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_argv'} = $line->{'argv'};
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_argv'}[0] = "_EXE_";
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'use_shell'} = $line->{'use_shell'} ? 1 : 0;
+	}
+    }
+
+    elsif ($event eq 'child_exit') {
+	if ($show_children == 1) {
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_code'} = $line->{'code'};
+	}
+    }
+
+    # TODO decide what information we want to test from thread events.
+
+    elsif ($event eq 'thread_start') {
+	if ($show_threads == 1) {
+	}
+    }
+
+    elsif ($event eq 'thread_exit') {
+	if ($show_threads == 1) {
+	}
+    }
+
+    # TODO decide what information we want to test from exec events.
+
+    elsif ($event eq 'exec') {
+	if ($show_exec == 1) {
+	}
+    }
+
+    elsif ($event eq 'exec_result') {
+	if ($show_exec == 1) {
+	}
+    }
+
+    elsif ($event eq 'def_param') {
+	# Accumulate parameter key/value pairs by key rather than in an array
+	# so that we get overwrite (last one wins) effects.
+	$processes->{$sid}->{'params'}->{$line->{'param'}} = $line->{'value'};
+    }
+
+    elsif ($event eq 'def_repo') {
+	# $processes->{$sid}->{'repos'}->{$line->{'repo'}} = $line->{'worktree'};
+	$processes->{$sid}->{'repos'}->{$line->{'repo'}} = "_WORKTREE_";
+    }
+
+    # A series of potentially nested and threaded region and data events
+    # is fundamentally incompatibile with the type of summary record we
+    # are building in this script.  Since they are intended for
+    # perf-trace-like analysis rather than a result summary, we ignore
+    # most of them here.
+
+    # elsif ($event eq 'region_enter') {
+    # }
+    # elsif ($event eq 'region_leave') {
+    # }
+
+    elsif ($event eq 'data') {
+	my $cat = $line->{'category'};
+	if ($cat eq 'test_category') {
+	    
+	    my $key = $line->{'key'};
+	    my $value = $line->{'value'};
+	    $processes->{$sid}->{'data'}->{$cat}->{$key} = $value;
+	}
+    }
+
+    # This trace2 target does not emit 'printf' events.
+    #
+    # elsif ($event eq 'printf') {
+    # }
+}
+
+# Dump the resulting hash into something that we can compare against
+# in the test script.  These options make Dumper output look a little
+# bit like JSON.  Also convert variable references of the form "$VAR*"
+# so that the matching HEREDOC doesn't need to escape it.
+
+$Data::Dumper::Sortkeys = 1;
+$Data::Dumper::Indent = 1;
+$Data::Dumper::Purity = 1;
+$Data::Dumper::Pair = ':';
+
+my $out = Dumper($processes);
+$out =~ s/'/"/g;
+$out =~ s/\$VAR/VAR/g;
+
+# Finally, if we're running this script to generate (manually confirmed)
+# data to add to the test script, guard the indentation.
+
+if ($gen_heredoc == 1) {
+    $out =~ s/^/\t\|/gms;
+}
+
+print $out;
diff --git a/t/t0400-pre-command-hook.sh b/t/t0400-pre-command-hook.sh
new file mode 100755
index 00000000000000..2ab9833af5cce1
--- /dev/null
+++ b/t/t0400-pre-command-hook.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='pre-command hook'
+
+. ./test-lib.sh
+
+test_expect_success 'with no hook' '
+	echo "first" > file &&
+	git add file &&
+	git commit -m "first"
+'
+
+test_expect_success 'with succeeding hook' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/pre-command <<-EOF &&
+	echo "\$*" | sed "s/ --git-pid=[0-9]*//" \
+		>\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	echo "second" >> file &&
+	git add file &&
+	test "add file" = "$(cat .git/pre-command.out)" &&
+	echo Hello | git hash-object --stdin &&
+	test "hash-object --stdin" = "$(cat .git/pre-command.out)"
+'
+
+test_expect_success 'with failing hook' '
+	write_script .git/hooks/pre-command <<-EOF &&
+	exit 1
+	EOF
+	echo "third" >> file &&
+	test_must_fail git add file &&
+	test_path_is_missing "$(cat .git/pre-command.out)"
+'
+
+test_expect_success 'in a subdirectory' '
+	echo touch i-was-here | write_script .git/hooks/pre-command &&
+	mkdir sub &&
+	(
+		cd sub &&
+		git version
+	) &&
+	test_path_is_file sub/i-was-here
+'
+
+test_expect_success 'in a subdirectory, using an alias' '
+	git reset --hard &&
+	echo "echo \"\$@; \$(pwd)\" >>log" |
+	write_script .git/hooks/pre-command &&
+	mkdir -p sub &&
+	(
+		cd sub &&
+		git -c alias.r="rebase HEAD" r
+	) &&
+	test_path_is_missing log &&
+	test_line_count = 2 sub/log
+'
+
+test_expect_success 'with core.hooksPath' '
+	mkdir -p .git/alternateHooks &&
+	write_script .git/alternateHooks/pre-command <<-EOF &&
+	echo "alternate" >\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	write_script .git/hooks/pre-command <<-EOF &&
+	echo "original"	>\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	git -c core.hooksPath=.git/alternateHooks status &&
+	test "alternate" = "$(cat .git/pre-command.out)"
+'
+test_done
diff --git a/t/t0401-post-command-hook.sh b/t/t0401-post-command-hook.sh
new file mode 100755
index 00000000000000..fcbfc4a0c79c1e
--- /dev/null
+++ b/t/t0401-post-command-hook.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+test_description='post-command hook'
+
+. ./test-lib.sh
+
+test_expect_success 'with no hook' '
+	echo "first" > file &&
+	git add file &&
+	git commit -m "first"
+'
+
+test_expect_success 'with succeeding hook' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/post-command <<-EOF &&
+	echo "\$*" | sed "s/ --git-pid=[0-9]*//" \
+		>\$(git rev-parse --git-dir)/post-command.out
+	EOF
+	echo "second" >> file &&
+	git add file &&
+	test "add file --exit_code=0" = "$(cat .git/post-command.out)"
+'
+
+test_expect_success 'with failing pre-command hook' '
+	write_script .git/hooks/pre-command <<-EOF &&
+	exit 1
+	EOF
+	echo "third" >> file &&
+	test_must_fail git add file &&
+	test_path_is_missing "$(cat .git/post-command.out)"
+'
+
+test_done
diff --git a/t/t0402-block-command-on-gvfs.sh b/t/t0402-block-command-on-gvfs.sh
new file mode 100755
index 00000000000000..3370abad464d50
--- /dev/null
+++ b/t/t0402-block-command-on-gvfs.sh
@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='block commands in GVFS repo'
+
+. ./test-lib.sh
+
+not_with_gvfs () {
+    command=$1 &&
+    shift &&
+    test_expect_success "test $command $*" "
+        test_config alias.g4rbled $command &&
+        test_config core.gvfs true &&
+        test_must_fail git $command $* &&
+        test_must_fail git g4rbled $* &&
+        test_unconfig core.gvfs &&
+        test_must_fail git -c core.gvfs=true $command $* &&
+        test_must_fail git -c core.gvfs=true g4rbled $*
+    "
+}
+
+not_with_gvfs fsck
+not_with_gvfs gc
+not_with_gvfs gc --auto
+not_with_gvfs prune
+not_with_gvfs repack
+not_with_gvfs submodule status
+not_with_gvfs update-index --index-version 2
+not_with_gvfs update-index --skip-worktree
+not_with_gvfs update-index --no-skip-worktree
+not_with_gvfs update-index --split-index
+not_with_gvfs worktree list
+
+test_expect_success 'test gc --auto succeeds when disabled via config' '
+	test_config core.gvfs true &&
+	test_config gc.auto 0 &&
+	git gc --auto
+'
+
+test_done
diff --git a/t/t0410/read-object b/t/t0410/read-object
new file mode 100755
index 00000000000000..2360d4916ee81c
--- /dev/null
+++ b/t/t0410/read-object
@@ -0,0 +1,118 @@
+#!/usr/bin/perl
+#
+# Example implementation for the Git read-object protocol version 1
+# See Documentation/technical/read-object-protocol.txt
+#
+# Allows you to test the ability for blobs to be pulled from a host git repo
+# "on demand."  Called when git needs a blob it couldn't find locally due to
+# a lazy clone that only cloned the commits and trees.
+#
+# A lazy clone can be simulated via the following commands from the host repo
+# you wish to create a lazy clone of:
+#
+# cd /host_repo
+# git rev-parse HEAD
+# git init /guest_repo
+# git cat-file --batch-check --batch-all-objects | grep -v 'blob' |
+#	cut -d' ' -f1 | git pack-objects /guest_repo/.git/objects/pack/noblobs
+# cd /guest_repo
+# git config core.virtualizeobjects true
+# git reset --hard <sha from rev-parse call above>
+#
+# Please note, this sample is a minimal skeleton. No proper error handling
+# was implemented.
+#
+
+use strict;
+use warnings;
+
+#
+# Point $DIR to the folder where your host git repo is located so we can pull
+# missing objects from it
+#
+my $DIR = "../.git/";
+
+sub packet_bin_read {
+	my $buffer;
+	my $bytes_read = read STDIN, $buffer, 4;
+	if ( $bytes_read == 0 ) {
+
+		# EOF - Git stopped talking to us!
+		exit();
+	}
+	elsif ( $bytes_read != 4 ) {
+		die "invalid packet: '$buffer'";
+	}
+	my $pkt_size = hex($buffer);
+	if ( $pkt_size == 0 ) {
+		return ( 1, "" );
+	}
+	elsif ( $pkt_size > 4 ) {
+		my $content_size = $pkt_size - 4;
+		$bytes_read = read STDIN, $buffer, $content_size;
+		if ( $bytes_read != $content_size ) {
+			die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
+		}
+		return ( 0, $buffer );
+	}
+	else {
+		die "invalid packet size: $pkt_size";
+	}
+}
+
+sub packet_txt_read {
+	my ( $res, $buf ) = packet_bin_read();
+	unless ( $buf =~ s/\n$// ) {
+		die "A non-binary line MUST be terminated by an LF.";
+	}
+	return ( $res, $buf );
+}
+
+sub packet_bin_write {
+	my $buf = shift;
+	print STDOUT sprintf( "%04x", length($buf) + 4 );
+	print STDOUT $buf;
+	STDOUT->flush();
+}
+
+sub packet_txt_write {
+	packet_bin_write( $_[0] . "\n" );
+}
+
+sub packet_flush {
+	print STDOUT sprintf( "%04x", 0 );
+	STDOUT->flush();
+}
+
+( packet_txt_read() eq ( 0, "git-read-object-client" ) ) || die "bad initialize";
+( packet_txt_read() eq ( 0, "version=1" ) )				 || die "bad version";
+( packet_bin_read() eq ( 1, "" ) )                       || die "bad version end";
+
+packet_txt_write("git-read-object-server");
+packet_txt_write("version=1");
+packet_flush();
+
+( packet_txt_read() eq ( 0, "capability=get" ) )    || die "bad capability";
+( packet_bin_read() eq ( 1, "" ) )                  || die "bad capability end";
+
+packet_txt_write("capability=get");
+packet_flush();
+
+while (1) {
+	my ($command) = packet_txt_read() =~ /^command=([^=]+)$/;
+
+	if ( $command eq "get" ) {
+		my ($sha1) = packet_txt_read() =~ /^sha1=([0-9a-f]{40})$/;
+		packet_bin_read();
+
+		system ('git --git-dir="' . $DIR . '" cat-file blob ' . $sha1 . ' | git -c core.virtualizeobjects=false hash-object -w --stdin >/dev/null 2>&1');
+		packet_txt_write(($?) ? "status=error" : "status=success");
+		packet_flush();
+
+		open my $log, '>>.git/read-object-hook.log';
+		print $log "Read object $sha1, exit code $?\n";
+		close $log;
+	} else {
+		die "bad command '$command'";
+	}
+}
diff --git a/t/t0411-read-object.sh b/t/t0411-read-object.sh
new file mode 100755
index 00000000000000..af97ec5b50f356
--- /dev/null
+++ b/t/t0411-read-object.sh
@@ -0,0 +1,34 @@
+#!/bin/sh
+
+test_description='tests for long running read-object process'
+
+. ./test-lib.sh
+
+test_expect_success 'setup host repo with a root commit' '
+	test_commit zero &&
+	hash1=$(git ls-tree HEAD | grep zero.t | cut -f1 | cut -d\  -f3)
+'
+
+test_expect_success 'blobs can be retrieved from the host repo' '
+	git init guest-repo &&
+	(cd guest-repo &&
+	 mkdir -p .git/hooks &&
+	 cp $TEST_DIRECTORY/t0410/read-object .git/hooks/ &&
+	 git config core.virtualizeobjects true &&
+	 git cat-file blob "$hash1")
+'
+
+test_expect_success 'invalid blobs generate errors' '
+	(cd guest-repo &&
+	 test_must_fail git cat-file blob "invalid")
+'
+
+test_expect_success 'read-object-hook is bypassed when writing objects' '
+	(cd guest-repo &&
+	 echo hello >hello.txt &&
+	 git add hello.txt &&
+	 hash="$(git rev-parse --verify :hello.txt)" &&
+	 ! grep "$hash" .git/read-object-hook.log)
+'
+
+test_done
diff --git a/t/t1016-read-tree-skip-sha-on-read.sh b/t/t1016-read-tree-skip-sha-on-read.sh
new file mode 100755
index 00000000000000..5b76a80a0020dc
--- /dev/null
+++ b/t/t1016-read-tree-skip-sha-on-read.sh
@@ -0,0 +1,22 @@
+#!/bin/sh
+
+test_description='check that read-tree works with core.gvfs config value'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-read-tree.sh
+
+test_expect_success setup '
+	echo one >a &&
+	git add a &&
+	git commit -m initial
+'
+test_expect_success 'read-tree without core.gvsf' '
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_expect_success 'read-tree with core.gvfs set to 1' '
+	git config core.gvfs 1 &&
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_done
diff --git a/t/t1090-sparse-checkout-scope.sh b/t/t1090-sparse-checkout-scope.sh
index 6e61b17c84d3e8..62735a6113c980 100755
--- a/t/t1090-sparse-checkout-scope.sh
+++ b/t/t1090-sparse-checkout-scope.sh
@@ -96,6 +96,23 @@ test_expect_success 'in partial clone, sparse checkout only fetches needed blobs
 	test_cmp expect actual
 '
 
+test_expect_success 'checkout does not delete items outside the sparse checkout file' '
+	git checkout master &&
+	git config core.gvfs 8 &&
+	git checkout -b outside &&
+	echo "new file1" >d &&
+	git add d &&
+	git commit -m "branch initial" &&
+	echo "new file1" >e &&
+	git add e &&
+	git commit -m "skipped worktree" &&
+	git update-index --skip-worktree e &&
+	echo "/d" >.git/info/sparse-checkout &&
+	git checkout HEAD^ &&
+	test_path_is_file d &&
+	test_path_is_file e
+'
+
 test_expect_success MINGW 'no unnecessary opendir() with fscache' '
 	git clone . fscache-test &&
 	(
diff --git a/t/t1092-virtualfilesystem.sh b/t/t1092-virtualfilesystem.sh
new file mode 100755
index 00000000000000..2379bca25a6426
--- /dev/null
+++ b/t/t1092-virtualfilesystem.sh
@@ -0,0 +1,370 @@
+#!/bin/sh
+
+test_description='virtual file system tests'
+
+. ./test-lib.sh
+
+clean_repo () {
+	rm .git/index &&
+	git -c core.virtualfilesystem= reset --hard HEAD &&
+	git -c core.virtualfilesystem= clean -fd &&
+	touch untracked.txt &&
+	touch dir1/untracked.txt &&
+	touch dir2/untracked.txt
+}
+
+test_expect_success 'setup' '
+	mkdir -p .git/hooks/ &&
+	cat > .gitignore <<-\EOF &&
+		.gitignore
+		expect*
+		actual*
+	EOF
+	mkdir -p dir1 &&
+	touch dir1/file1.txt &&
+	touch dir1/file2.txt &&
+	mkdir -p dir2 &&
+	touch dir2/file1.txt &&
+	touch dir2/file2.txt &&
+	git add . &&
+	git commit -m "initial" &&
+	git config --local core.virtualfilesystem .git/hooks/virtualfilesystem
+'
+
+test_expect_success 'test hook parameters and version' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		if test "$#" -ne 1
+		then
+			echo "$0: Exactly 1 argument expected" >&2
+			exit 2
+		fi
+
+		if test "$1" != 1
+		then
+			echo "$0: Unsupported hook version." >&2
+			exit 1
+		fi
+	EOF
+	git status &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		exit 3
+	EOF
+	test_must_fail git status
+'
+
+test_expect_success 'verify status is clean' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir2/file1.txt\0"
+	EOF
+	rm -f .git/index &&
+	git checkout -f &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir2/file1.txt\0"
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+	EOF
+	git status > actual &&
+	cat > expected <<-\EOF &&
+		On branch master
+		nothing to commit, working tree clean
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify skip-worktree bit is set for absolute path' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		S dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify skip-worktree bit is cleared for absolute path' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file2.txt\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		S dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify folder wild cards' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify folders not included are ignored' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify including one file doesnt include the rest' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+		printf "dir1/dir2/a\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/dir2/a
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify files not listed are ignored by git clean -f -x' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "untracked.txt\0"
+		printf "dir1/\0"
+	EOF
+	mkdir -p dir3 &&
+	touch dir3/untracked.txt &&
+	git clean -f -x &&
+	test ! -f untracked.txt &&
+	test -d dir1 &&
+	test -f dir1/file1.txt &&
+	test -f dir1/file2.txt &&
+	test ! -f dir1/untracked.txt &&
+	test -f dir2/file1.txt &&
+	test -f dir2/file2.txt &&
+	test -f dir2/untracked.txt &&
+	test -d dir3 &&
+	test -f dir3/untracked.txt
+'
+
+test_expect_success 'verify files not listed are ignored by git clean -f -d -x' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "untracked.txt\0"
+		printf "dir1/\0"
+		printf "dir3/\0"
+	EOF
+	mkdir -p dir3 &&
+	touch dir3/untracked.txt &&
+	git clean -f -d -x &&
+	test ! -f untracked.txt &&
+	test -d dir1 &&
+	test -f dir1/file1.txt &&
+	test -f dir1/file2.txt &&
+	test ! -f dir1/untracked.txt &&
+	test -f dir2/file1.txt &&
+	test -f dir2/file2.txt &&
+	test -f dir2/untracked.txt &&
+	test ! -d dir3 &&
+	test ! -f dir3/untracked.txt
+'
+
+test_expect_success 'verify folder entries include all files' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+		?? dir1/b
+		?? dir1/dir2/a
+		?? dir1/dir2/b
+		?? dir1/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify case insensitivity of virtual file system entries' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/a\0"
+		printf "Dir1/Dir2/a\0"
+		printf "DIR2/\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git -c core.ignorecase=false status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+	EOF
+	test_cmp expected actual &&
+	git -c core.ignorecase=true status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+		?? dir1/dir2/a
+		?? dir2/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file created' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file3.txt\0"
+	EOF
+	touch dir1/file3.txt &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		S dir1/file1.txt
+		S dir1/file2.txt
+		H dir1/file3.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file renamed' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file3.txt\0"
+	EOF
+	mv dir1/file1.txt dir1/file3.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+		?? dir1/file3.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file deleted' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	rm dir1/file1.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file overwritten' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	echo "overwritten" > dir1/file1.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 M dir1/file1.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on folder created' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/dir1/\0"
+	EOF
+	mkdir -p dir1/dir1 &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+	EOF
+	test_cmp expected actual &&
+	git clean -fd &&
+	test ! -d "/dir1/dir1"
+'
+
+test_expect_success 'on folder renamed' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir3/\0"
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+		printf "dir3/file1.txt\0"
+		printf "dir3/file2.txt\0"
+	EOF
+	mv dir1 dir3 &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+		 D dir1/file2.txt
+		?? dir3/file1.txt
+		?? dir3/file2.txt
+		?? dir3/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'folder with same prefix as file' '
+	clean_repo &&
+	touch dir1.sln &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+		printf "dir1.sln\0"
+	EOF
+	git add dir1.sln &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1.sln
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_done
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 70926b5bc04643..13af72e994df00 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -348,4 +348,130 @@ test_expect_success 'verify incorrect 64-bit offset' '
 		"incorrect object offset"
 '
 
+test_expect_success 'setup expire tests' '
+	mkdir dup &&
+	(
+		cd dup &&
+		git init &&
+		for i in $(test_seq 1 20)
+		do
+			test_commit $i
+		done &&
+		git branch A HEAD &&
+		git branch B HEAD~8 &&
+		git branch C HEAD~13 &&
+		git branch D HEAD~16 &&
+		git branch E HEAD~18 &&
+		git pack-objects --revs .git/objects/pack/pack-E <<-EOF &&
+		refs/heads/E
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-D <<-EOF &&
+		refs/heads/D
+		^refs/heads/E
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-C <<-EOF &&
+		refs/heads/C
+		^refs/heads/D
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-B <<-EOF &&
+		refs/heads/B
+		^refs/heads/C
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-A <<-EOF &&
+		refs/heads/A
+		^refs/heads/B
+		EOF
+		git multi-pack-index write
+	)
+'
+
+test_expect_success 'expire does not remove any packs' '
+	(
+		cd dup &&
+		ls .git/objects/pack >expect &&
+		git multi-pack-index expire &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'expire removes unreferenced packs' '
+	(
+		cd dup &&
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/A
+		^refs/heads/C
+		EOF
+		git multi-pack-index write &&
+		ls .git/objects/pack | grep -v -e pack-[AB] >expect &&
+		git multi-pack-index expire &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'repack with minimum size does not alter existing packs' '
+	(
+		cd dup &&
+		ls .git/objects/pack >expect &&
+		MINSIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 1) &&
+		git multi-pack-index repack --batch-size=$MINSIZE &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'repack creates a new pack' '
+	(
+		cd dup &&
+		SECOND_SMALLEST_SIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 2 | tail -n 1) &&
+		BATCH_SIZE=$(($SECOND_SMALLEST_SIZE + 1)) &&
+		git multi-pack-index repack --batch-size=$BATCH_SIZE &&
+		ls .git/objects/pack/*idx >idx-list &&
+		test_line_count = 5 idx-list &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 5 midx-list
+	)
+'
+
+test_expect_success 'expire removes repacked packs' '
+	(
+		cd dup &&
+		ls -S .git/objects/pack/*pack | head -n 3 >expect &&
+		git multi-pack-index expire &&
+		ls -S .git/objects/pack/*pack >actual &&
+		test_cmp expect actual &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 3 midx-list
+	)
+'
+
+test_expect_success 'expire works when adding new packs' '
+	(
+		cd dup &&
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/A
+		^refs/heads/B
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/B
+		^refs/heads/C
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/C
+		^refs/heads/D
+		EOF
+		git multi-pack-index write &&
+		git pack-objects --revs .git/objects/pack/pack-a <<-EOF &&
+		refs/heads/D
+		^refs/heads/E
+		EOF
+		git multi-pack-index write &&
+		git pack-objects --revs .git/objects/pack/pack-z <<-EOF &&
+		refs/heads/E
+		EOF
+		git multi-pack-index expire &&	
+		git multi-pack-index verify
+	)
+'
 test_done
diff --git a/t/t5582-vfs.sh b/t/t5582-vfs.sh
new file mode 100755
index 00000000000000..8a703cbb640387
--- /dev/null
+++ b/t/t5582-vfs.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_description='fetch using the flag to skip reachability and upload pack'
+
+. ./test-lib.sh
+
+
+test_expect_success setup '
+	echo inital >a &&
+	git add a &&
+	git commit -m initial &&
+	git clone . one
+'
+
+test_expect_success "fetch test" '
+	cd one &&
+	git config core.gvfs 16 &&
+	rm -rf .git/objects/* &&
+	git -C .. cat-file commit HEAD | git hash-object -w --stdin -t commit &&
+	git fetch &&
+	test_must_fail git rev-parse --verify HEAD^{tree}
+'
+
+test_done
\ No newline at end of file
diff --git a/t/t6040-tracking-info.sh b/t/t6040-tracking-info.sh
index 716283b274677d..febf63f28a54cd 100755
--- a/t/t6040-tracking-info.sh
+++ b/t/t6040-tracking-info.sh
@@ -159,6 +159,19 @@ test_expect_success 'status -s -b --no-ahead-behind (diverged from upstream)' '
 	test_i18ncmp expect actual
 '
 
+cat >expect <<\EOF
+## b1...origin/master [different]
+EOF
+
+test_expect_success 'status.aheadbehind=false status -s -b (diverged from upstream)' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=false status -s -b | head -1
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 On branch b1
 Your branch and 'origin/master' have diverged,
@@ -174,6 +187,15 @@ test_expect_success 'status --long --branch' '
 	test_i18ncmp expect actual
 '
 
+test_expect_success 'status --long --branch' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=true status --long -b | head -3
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 On branch b1
 Your branch and 'origin/master' refer to different commits.
@@ -188,6 +210,15 @@ test_expect_success 'status --long --branch --no-ahead-behind' '
 	test_i18ncmp expect actual
 '
 
+test_expect_success 'status.aheadbehind=false status --long --branch' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=false status --long -b | head -2
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 ## b5...brokenbase [gone]
 EOF
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index 4684d06552ac2e..53258d45a12553 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -162,7 +162,15 @@ test_expect_success 'background auto gc respects lock for all operations' '
 	# now fake a concurrent gc that holds the lock; we can use our
 	# shell pid so that it looks valid.
 	hostname=$(hostname || echo unknown) &&
-	printf "$$ %s" "$hostname" >.git/gc.pid &&
+	shell_pid=$$ &&
+	if test_have_prereq MINGW && test -f /proc/$shell_pid/winpid
+	then
+		# In Git for Windows, Bash (actually, the MSYS2 runtime) has a
+		# different idea of PIDs than git.exe (actually Windows). Use
+		# the Windows PID in this case.
+		shell_pid=$(cat /proc/$shell_pid/winpid)
+	fi &&
+	printf "%d %s" "$shell_pid" "$hostname" >.git/gc.pid &&
 
 	# our gc should exit zero without doing anything
 	run_and_wait_for_auto_gc &&
diff --git a/t/t7064-wtstatus-pv2.sh b/t/t7064-wtstatus-pv2.sh
index 11eccc231a792b..537787e598b414 100755
--- a/t/t7064-wtstatus-pv2.sh
+++ b/t/t7064-wtstatus-pv2.sh
@@ -445,6 +445,14 @@ test_expect_success 'verify --[no-]ahead-behind with V2 format' '
 		EOF
 
 		git status --ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm that "status.aheadbehind" DOES NOT work on V2 format.
+		git -c status.aheadbehind=false status --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm that "status.aheadbehind" DOES NOT work on V2 format.
+		git -c status.aheadbehind=true status --porcelain=v2 --branch --untracked-files=all >actual &&
 		test_cmp expect actual
 	)
 '
diff --git a/t/t7108-reset-stdin.sh b/t/t7108-reset-stdin.sh
index b7cbcbf869296c..db5483b8f10052 100755
--- a/t/t7108-reset-stdin.sh
+++ b/t/t7108-reset-stdin.sh
@@ -29,4 +29,13 @@ test_expect_success '--stdin requires --mixed' '
 	git reset --mixed --stdin <list
 '
 
+
+test_expect_success '--stdin trims carriage returns' '
+	test_commit endline &&
+	git rm endline.t &&
+	printf "endline.t\r\n" >list &&
+	git reset --stdin <list &&
+	test endline.t = "$(git ls-files endline.t)"
+'
+
 test_done
diff --git a/t/t7113-post-index-changed-hook.sh b/t/t7113-post-index-changed-hook.sh
new file mode 100755
index 00000000000000..5aeb726e375d26
--- /dev/null
+++ b/t/t7113-post-index-changed-hook.sh
@@ -0,0 +1,144 @@
+#!/bin/sh
+
+test_description='post index changed hook'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir -p dir1 &&
+	touch dir1/file1.txt &&
+	echo testing >dir1/file2.txt &&
+	git add . &&
+	git commit -m "initial"
+'
+
+test_expect_success 'test status, add, commit, others trigger hook without flags set' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir is set." >testfailure
+			exit 1
+		fi
+		if test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_skipworktree is set." >testfailure
+			exit 1
+		fi
+		if test -f ".git/index.lock"; then
+			echo ".git/index.lock exists" >testfailure
+			exit 3
+		fi
+		if ! test -f ".git/index"; then
+			echo ".git/index does not exist" >testfailure
+			exit 3
+		fi
+		echo "success" >testsuccess
+	EOF
+	mkdir -p dir2 &&
+	touch dir2/file1.txt &&
+	touch dir2/file2.txt &&
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git status &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git add . &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git commit -m "second" &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -- dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure &&
+	git reset --soft &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test checkout and reset trigger the hook' '
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$1" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_workdir set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_workdir set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "update_workdir should be set for checkout" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout master &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout HEAD &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --hard &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -B test &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test reset --mixed and update-index triggers the hook' '
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$2" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_skipworktree set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_skipworktree set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "updated_skipworktree should be set for reset --mixed and update-index" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --mixed --quiet HEAD~1 &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git hash-object -w --stdin <dir1/file2.txt >expect &&
+	git update-index --cacheinfo 100644 "$(cat expect)" dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index --skip-worktree dir1/file2.txt &&
+	git update-index --remove dir1/file2.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_done
diff --git a/t/t7114-reset-sparse-checkout.sh b/t/t7114-reset-sparse-checkout.sh
new file mode 100755
index 00000000000000..8dd88fd46d3938
--- /dev/null
+++ b/t/t7114-reset-sparse-checkout.sh
@@ -0,0 +1,58 @@
+#!/bin/sh
+
+test_description='reset when using a sparse-checkout'
+
+. ./test-lib.sh
+
+# reset using a sparse-checkout file
+
+test_expect_success 'setup' '
+	test_tick &&
+	echo "checkout file" >c &&
+	echo "modify file" >m &&
+	echo "delete file" >d &&
+	git add . &&
+	git commit -m "initial commit" &&
+	echo "added file" >a &&
+	echo "modification of a file" >m &&
+	git rm d &&
+	git add . &&
+	git commit -m "second commit" &&
+	git checkout -b endCommit
+'
+
+test_expect_success 'reset when there is a sparse-checkout' '
+	echo "/c" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -b resetBranch &&
+	test_path_is_missing m &&
+	test_path_is_missing a &&
+	test_path_is_missing d &&
+	git reset HEAD~1 &&
+	test "checkout file" = "$(cat c)" &&
+	test "modification of a file" = "$(cat m)" &&
+	test "added file" = "$(cat a)" &&
+	test_path_is_missing d
+'
+
+test_expect_success 'reset after deleting file without skip-worktree bit' '
+	git checkout -f endCommit &&
+	git clean -xdf &&
+	echo "/c
+/m" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -b resetAfterDelete &&
+	test_path_is_file m &&
+	test_path_is_missing a &&
+	test_path_is_missing d &&
+	rm -f m &&
+	git reset HEAD~1 &&
+	test "checkout file" = "$(cat c)" &&
+	test "added file" = "$(cat a)" &&
+	test_path_is_missing m &&
+	test_path_is_missing d
+'
+
+
+
+test_done
diff --git a/t/t7523-status-complete-untracked.sh b/t/t7523-status-complete-untracked.sh
new file mode 100755
index 00000000000000..2f4476654a5570
--- /dev/null
+++ b/t/t7523-status-complete-untracked.sh
@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='git status untracked complete tests'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	cat >.gitignore <<-\EOF &&
+	*.ign
+	ignored_dir/
+	EOF
+
+	mkdir tracked ignored_dir &&
+	touch tracked_1.txt tracked/tracked_1.txt &&
+	git add . &&
+	test_tick &&
+	git commit -m"Adding original file." &&
+	mkdir untracked &&
+	touch ignored.ign ignored_dir/ignored_2.txt \
+	      untracked_1.txt untracked/untracked_2.txt untracked/untracked_3.txt
+'
+
+test_expect_success 'verify untracked-files=complete' '
+	cat >expect <<-\EOF &&
+	? expect
+	? output
+	? untracked/
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --porcelain=v2 --untracked-files=complete --ignored >output &&
+	test_i18ncmp expect output
+'
+
+test_done
diff --git a/t/t7524-serialized-status.sh b/t/t7524-serialized-status.sh
new file mode 100755
index 00000000000000..d157fa98d0464e
--- /dev/null
+++ b/t/t7524-serialized-status.sh
@@ -0,0 +1,336 @@
+#!/bin/sh
+
+test_description='git serialized status tests'
+
+. ./test-lib.sh
+
+# This file includes tests for serializing / deserializing
+# status data. These tests cover two basic features:
+#
+# [1] Because users can request different types of untracked-file
+#     and ignored file reporting, the cache data generated by
+#     serialize must use either the same untracked and ignored
+#     parameters as the later deserialize invocation; otherwise,
+#     the deserialize invocation must disregard the cached data
+#     and run a full scan itself.
+#
+#     To increase the number of cases where the cached status can
+#     be used, we have added a "--untracked-file=complete" option
+#     that reports a superset or union of the results from the
+#     "-u normal" and "-u all".  We combine this with a filter in
+#     deserialize to filter the results.
+#
+#     Ignored file reporting is simpler in that is an all or
+#     nothing; there are no subsets.
+#
+#     The tests here (in addition to confirming that a cache
+#     file can be generated and used by a subsequent status
+#     command) need to test this untracked-file filtering.
+#
+# [2] ensuring the status calls are using data from the status
+#     cache as expected.  This includes verifying cached data
+#     is used when appropriate as well as falling back to
+#     performing a new status scan when the data in the cache
+#     is insufficient/known stale.
+
+test_expect_success 'setup' '
+	cat >.gitignore <<-\EOF &&
+	*.ign
+	ignored_dir/
+	EOF
+
+	mkdir tracked ignored_dir &&
+	touch tracked_1.txt tracked/tracked_1.txt &&
+	git add . &&
+	test_tick &&
+	git commit -m"Adding original file." &&
+	mkdir untracked &&
+	touch ignored.ign ignored_dir/ignored_2.txt \
+	      untracked_1.txt untracked/untracked_2.txt untracked/untracked_3.txt
+'
+
+test_expect_success 'verify untracked-files=complete with no conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --untracked-files=complete --ignored=matching --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify untracked-files=complete to untracked-files=normal conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify untracked-files=complete to untracked-files=all conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --untracked-files=all --ignored=matching --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify serialized status with non-convertible ignore mode does new scan' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? new_change.txt
+	? output
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --ignored --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify serialized status handles path scopes' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? untracked/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat untracked >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify no-ahead-behind and serialized status integration' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	# branch.oid 68d4a437ea4c2de65800f48c053d4d543b55c410
+	# branch.head alt_branch
+	# branch.upstream master
+	# branch.ab +1 -0
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	git checkout -b alt_branch master --track >/dev/null &&
+	touch alt_branch_changes.txt &&
+	git add alt_branch_changes.txt &&
+	test_tick &&
+	git commit -m"New commit on alt branch"  &&
+
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git -c status.aheadBehind=false status --porcelain=v2 --branch --ahead-behind --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify new --serialize=path mode' '
+	test_when_finished "rm serialized_status.dat expect new_change.txt output.1 output.2" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? output.1
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	git checkout -b serialize_path_branch master --track >/dev/null &&
+	touch alt_branch_changes.txt &&
+	git add alt_branch_changes.txt &&
+	test_tick &&
+	git commit -m"New commit on serialize_path_branch"  &&
+
+	git status --porcelain=v2 --serialize=serialized_status.dat >output.1 &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output.2 &&
+	test_i18ncmp expect output.1 &&
+	test_i18ncmp expect output.2
+'
+
+test_expect_success 'try deserialize-wait feature' '
+	test_when_finished "rm -f serialized_status.dat dirt expect.* output.* trace.*" &&
+
+	git status --serialize=serialized_status.dat >output.1 &&
+
+	# make status cache stale by updating the mtime on the index.  confirm that
+	# deserialize fails when requested.
+	sleep 1 &&
+	touch .git/index &&
+	test_must_fail git status --deserialize=serialized_status.dat --deserialize-wait=fail &&
+	test_must_fail git -c status.deserializeWait=fail status --deserialize=serialized_status.dat &&
+
+	cat >expect.1 <<-\EOF &&
+	? expect.1
+	? output.1
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	# refresh the status cache.
+	git status --porcelain=v2 --serialize=serialized_status.dat >output.1 &&
+	test_cmp expect.1 output.1 &&
+
+	# create some dirt. confirm deserialize used the existing status cache.
+	echo x >dirt &&
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output.2 &&
+	test_cmp output.1 output.2 &&
+
+	# make the cache stale and try the timeout feature and wait upto
+	# 2 tenths of a second.  confirm deserialize timed out and rejected
+	# the status cache and did a normal scan.
+
+	cat >expect.2 <<-\EOF &&
+	? dirt
+	? expect.1
+	? expect.2
+	? output.1
+	? output.2
+	? serialized_status.dat
+	? trace.2
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	sleep 1 &&
+	touch .git/index &&
+	GIT_TRACE_DESERIALIZE=1 git status --porcelain=v2 --deserialize=serialized_status.dat --deserialize-wait=2 >output.2 2>trace.2 &&
+	test_cmp expect.2 output.2 &&
+	grep "wait polled=2 result=1" trace.2 >trace.2g
+'
+
+test_expect_success 'merge conflicts' '
+
+	# create a merge conflict.
+
+	git init conflicts &&
+	echo x >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m x &&
+	git -C conflicts branch a &&
+	git -C conflicts branch b &&
+	git -C conflicts checkout a &&
+	echo y >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m a &&
+	git -C conflicts checkout b &&
+	echo z >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m b &&
+	test_must_fail git -C conflicts merge --no-commit a &&
+
+	# verify that regular status correctly identifies it
+	# in each format.
+
+	cat >expect.v2 <<EOF &&
+u UU N... 100644 100644 100644 100644 587be6b4c3f93f93c489c0111bba5596147a26cb b68025345d5301abad4d9ec9166f455243a0d746 975fbec8256d3e8a3797e7a3611380f27c49f4ac x.txt
+EOF
+	git -C conflicts status --porcelain=v2 >observed.v2 &&
+	test_cmp expect.v2 observed.v2 &&
+
+	cat >expect.long <<EOF &&
+On branch b
+You have unmerged paths.
+  (fix conflicts and run "git commit")
+  (use "git merge --abort" to abort the merge)
+
+Unmerged paths:
+  (use "git add <file>..." to mark resolution)
+
+	both modified:   x.txt
+
+no changes added to commit (use "git add" and/or "git commit -a")
+EOF
+	git -C conflicts status --long >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	cat >expect.short <<EOF &&
+UU x.txt
+EOF
+	git -C conflicts status --short >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# save status data in serialized cache.
+
+	git -C conflicts status --serialize >serialized &&
+
+	# make some dirt in the worktree so we can tell whether subsequent
+	# status commands used the cached data or did a fresh status.
+
+	echo dirt >conflicts/dirt.txt &&
+
+	# run status using the cached data.
+
+	git -C conflicts status --long --deserialize=../serialized >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	git -C conflicts status --short --deserialize=../serialized >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# currently, the cached data does not have enough information about
+	# merge conflicts for porcelain V2 format.  (And V2 format looks at
+	# the index to get that data, but the whole point of the serialization
+	# is to avoid reading the index unnecessarily.)  So V2 always rejects
+	# the cached data when there is an unresolved conflict.
+
+	cat >expect.v2.dirty <<EOF &&
+u UU N... 100644 100644 100644 100644 587be6b4c3f93f93c489c0111bba5596147a26cb b68025345d5301abad4d9ec9166f455243a0d746 975fbec8256d3e8a3797e7a3611380f27c49f4ac x.txt
+? dirt.txt
+EOF
+	git -C conflicts status --porcelain=v2 --deserialize=../serialized >observed.v2 &&
+	test_cmp expect.v2.dirty observed.v2
+
+'
+
+test_expect_success 'renames' '
+	git init rename_test &&
+	echo OLDNAME >rename_test/OLDNAME &&
+	git -C rename_test add OLDNAME &&
+	git -C rename_test commit -m OLDNAME &&
+	git -C rename_test mv OLDNAME NEWNAME &&
+	git -C rename_test status --serialize=renamed.dat >output.1 &&
+	echo DIRT >rename_test/DIRT &&
+	git -C rename_test status --deserialize=renamed.dat >output.2 &&
+	test_i18ncmp output.1 output.2
+'
+
+test_done
diff --git a/t/t7615-merge-sparse-checkout.sh b/t/t7615-merge-sparse-checkout.sh
new file mode 100755
index 00000000000000..8e8208a61d39eb
--- /dev/null
+++ b/t/t7615-merge-sparse-checkout.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+test_description='merge can handle sparse-checkout'
+
+. ./test-lib.sh
+
+# merges with conflicts
+
+test_expect_success 'setup' '
+	test_commit a &&
+	test_commit file &&
+	git checkout -b delete-file &&
+	git rm file.t &&
+	test_tick &&
+	git commit -m "remove file" &&
+	git checkout master &&
+	test_commit modify file.t changed
+'
+
+test_expect_success 'merge conflict deleted file and modified' '
+	echo "/a.t" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -f &&
+	test_path_is_missing file.t &&
+	test_must_fail git merge delete-file &&
+	test_path_is_file file.t &&
+	test "changed" = "$(cat file.t)"
+'
+
+test_done
diff --git a/t/t9822-git-p4-path-encoding.sh b/t/t9822-git-p4-path-encoding.sh
index c78477c19b4330..de0b46581d3207 100755
--- a/t/t9822-git-p4-path-encoding.sh
+++ b/t/t9822-git-p4-path-encoding.sh
@@ -7,6 +7,13 @@ test_description='Clone repositories with non ASCII paths'
 UTF8_ESCAPED="a-\303\244_o-\303\266_u-\303\274.txt"
 ISO8859_ESCAPED="a-\344_o-\366_u-\374.txt"
 
+ISO8859="$(printf "$ISO8859_ESCAPED")" &&
+echo content123 >"$ISO8859" &&
+rm "$ISO8859" || {
+	skip_all="fs does not accept ISO-8859-1 filenames"
+	test_done
+}
+
 test_expect_success 'start p4d' '
 	start_p4d
 '
diff --git a/trace2.c b/trace2.c
new file mode 100644
index 00000000000000..6baa65cdf9aee6
--- /dev/null
+++ b/trace2.c
@@ -0,0 +1,778 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "quote.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "thread-utils.h"
+#include "version.h"
+#include "trace2/tr2_cfg.h"
+#include "trace2/tr2_cmd_name.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_sysenv.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static int trace2_enabled;
+
+static int tr2_next_child_id; /* modify under lock */
+static int tr2_next_exec_id; /* modify under lock */
+static int tr2_next_repo_id = 1; /* modify under lock. zero is reserved */
+
+/*
+ * A table of the builtin TRACE2 targets.  Each of these may be independently
+ * enabled or disabled.  Each TRACE2 API method will try to write an event to
+ * *each* of the enabled targets.
+ */
+/* clang-format off */
+static struct tr2_tgt *tr2_tgt_builtins[] =
+{
+	&tr2_tgt_normal,
+	&tr2_tgt_perf,
+	&tr2_tgt_event,
+	NULL
+};
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_builtin(j, tgt_j)			\
+	for (j = 0, tgt_j = tr2_tgt_builtins[j];	\
+	     tgt_j;					\
+	     j++, tgt_j = tr2_tgt_builtins[j])
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_wanted_builtin(j, tgt_j)            \
+	for_each_builtin(j, tgt_j)                   \
+		if (tr2_dst_trace_want(tgt_j->pdst))
+/* clang-format on */
+
+/*
+ * Force (rather than lazily) initialize any of the requested
+ * builtin TRACE2 targets at startup (and before we've seen an
+ * actual TRACE2 event call) so we can see if we need to setup
+ * the TR2 and TLS machinery.
+ *
+ * Return the number of builtin targets enabled.
+ */
+static int tr2_tgt_want_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	int sum = 0;
+
+	for_each_builtin (j, tgt_j)
+		if (tgt_j->pfn_init())
+			sum++;
+
+	return sum;
+}
+
+/*
+ * Properly terminate each builtin target.  Give each target
+ * a chance to write a summary event and/or flush if necessary
+ * and then close the fd.
+ */
+static void tr2_tgt_disable_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	for_each_builtin (j, tgt_j)
+		tgt_j->pfn_term();
+}
+
+static int tr2main_exit_code;
+
+/*
+ * Our atexit routine should run after everything has finished.
+ *
+ * Note that events generated here might not actually appear if
+ * we are writing to fd 1 or 2 and our atexit routine runs after
+ * the pager's atexit routine (since it closes them to shutdown
+ * the pipes).
+ */
+static void tr2main_atexit_handler(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions so that our atexit message
+	 * does not appear nested.  This improves the appearance of
+	 * the trace output if someone calls die(), for example.
+	 */
+	tr2tls_pop_unwind_self();
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_atexit)
+			tgt_j->pfn_atexit(us_elapsed_absolute,
+					  tr2main_exit_code);
+
+	tr2_tgt_disable_builtins();
+
+	tr2tls_release();
+	tr2_sid_release();
+	tr2_cmd_name_release();
+	tr2_cfg_free_patterns();
+	tr2_sysenv_release();
+
+	trace2_enabled = 0;
+}
+
+static void tr2main_signal_handler(int signo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_signal)
+			tgt_j->pfn_signal(us_elapsed_absolute, signo);
+
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+void trace2_initialize_clock(void)
+{
+	tr2tls_start_process_clock();
+}
+
+void trace2_initialize_fl(const char *file, int line)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (trace2_enabled)
+		return;
+
+	tr2_sysenv_load();
+
+	if (!tr2_tgt_want_builtins())
+		return;
+	trace2_enabled = 1;
+
+	tr2_sid_get();
+
+	atexit(tr2main_atexit_handler);
+	sigchain_push(SIGPIPE, tr2main_signal_handler);
+	tr2tls_init();
+
+	/*
+	 * Emit 'version' message on each active builtin target.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_version_fl)
+			tgt_j->pfn_version_fl(file, line);
+}
+
+int trace2_is_enabled(void)
+{
+	return trace2_enabled;
+}
+
+void trace2_cmd_start_fl(const char *file, int line, const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_start_fl)
+			tgt_j->pfn_start_fl(file, line, us_elapsed_absolute,
+					    argv);
+}
+
+int trace2_cmd_exit_fl(const char *file, int line, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	code &= 0xff;
+
+	if (!trace2_enabled)
+		return code;
+
+	trace2_collect_process_info(TRACE2_PROCESS_INFO_EXIT);
+
+	tr2main_exit_code = code;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exit_fl)
+			tgt_j->pfn_exit_fl(file, line, us_elapsed_absolute,
+					   code);
+
+	return code;
+}
+
+void trace2_cmd_error_va_fl(const char *file, int line, const char *fmt,
+			    va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy (because an 'ap' can only be walked once).
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_error_va_fl)
+			tgt_j->pfn_error_va_fl(file, line, fmt, ap);
+}
+
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_path_fl)
+			tgt_j->pfn_command_path_fl(file, line, pathname);
+}
+
+void trace2_cmd_name_fl(const char *file, int line, const char *name)
+{
+	struct tr2_tgt *tgt_j;
+	const char *hierarchy;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	tr2_cmd_name_append_hierarchy(name);
+	hierarchy = tr2_cmd_name_get_hierarchy();
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_name_fl)
+			tgt_j->pfn_command_name_fl(file, line, name, hierarchy);
+}
+
+void trace2_cmd_mode_fl(const char *file, int line, const char *mode)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_mode_fl)
+			tgt_j->pfn_command_mode_fl(file, line, mode);
+}
+
+void trace2_cmd_alias_fl(const char *file, int line, const char *alias,
+			 const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_alias_fl)
+			tgt_j->pfn_alias_fl(file, line, alias, argv);
+}
+
+void trace2_cmd_list_config_fl(const char *file, int line)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_list_config_fl(file, line);
+}
+
+void trace2_cmd_set_config_fl(const char *file, int line, const char *key,
+			      const char *value)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_set_fl(file, line, key, value);
+}
+
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	cmd->trace2_child_id = tr2tls_locked_increment(&tr2_next_child_id);
+	cmd->trace2_child_us_start = us_now;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_child_start_fl)
+			tgt_j->pfn_child_start_fl(file, line,
+						  us_elapsed_absolute, cmd);
+}
+
+void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
+			  int child_exit_code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_child;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	if (cmd->trace2_child_us_start)
+		us_elapsed_child = us_now - cmd->trace2_child_us_start;
+	else
+		us_elapsed_child = 0;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_child_exit_fl)
+			tgt_j->pfn_child_exit_fl(file, line,
+						 us_elapsed_absolute,
+						 cmd->trace2_child_id, cmd->pid,
+						 child_exit_code,
+						 us_elapsed_child);
+}
+
+int trace2_exec_fl(const char *file, int line, const char *exe,
+		   const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	int exec_id;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return -1;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	exec_id = tr2tls_locked_increment(&tr2_next_exec_id);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exec_fl)
+			tgt_j->pfn_exec_fl(file, line, us_elapsed_absolute,
+					   exec_id, exe, argv);
+
+	return exec_id;
+}
+
+void trace2_exec_result_fl(const char *file, int line, int exec_id, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exec_result_fl)
+			tgt_j->pfn_exec_result_fl(
+				file, line, us_elapsed_absolute, exec_id, code);
+}
+
+void trace2_thread_start_fl(const char *file, int line, const char *thread_name)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread()) {
+		/*
+		 * We should only be called from the new thread's thread-proc,
+		 * so this is technically a bug.  But in those cases where the
+		 * main thread also runs the thread-proc function (or when we
+		 * are built with threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-enter so the nesting looks
+		 * correct.
+		 */
+		trace2_region_enter_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main: %s",
+					      thread_name);
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	tr2tls_create_self(thread_name, us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_thread_start_fl)
+			tgt_j->pfn_thread_start_fl(file, line,
+						   us_elapsed_absolute);
+}
+
+void trace2_thread_exit_fl(const char *file, int line)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_thread;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread()) {
+		/*
+		 * We should only be called from the exiting thread's
+		 * thread-proc, so this is technically a bug.  But in
+		 * those cases where the main thread also runs the
+		 * thread-proc function (or when we are built with
+		 * threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-leave so the nesting
+		 * looks correct.
+		 */
+		trace2_region_leave_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main");
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions and then get the relative time
+	 * for the outer-most region (which we pushed when the thread
+	 * started).  This gives us the run time of the thread.
+	 */
+	tr2tls_pop_unwind_self();
+	us_elapsed_thread = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_thread_exit_fl)
+			tgt_j->pfn_thread_exit_fl(file, line,
+						  us_elapsed_absolute,
+						  us_elapsed_thread);
+
+	tr2tls_unset_self();
+}
+
+void trace2_def_param_fl(const char *file, int line, const char *param,
+			 const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_param_fl)
+			tgt_j->pfn_param_fl(file, line, param, value);
+}
+
+void trace2_def_repo_fl(const char *file, int line, struct repository *repo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	if (repo->trace2_repo_id)
+		return;
+
+	repo->trace2_repo_id = tr2tls_locked_increment(&tr2_next_repo_id);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_repo_fl)
+			tgt_j->pfn_repo_fl(file, line, repo);
+}
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Print the region-enter message at the current nesting
+	 * (indentation) level and then push a new level.
+	 *
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_region_enter_printf_va_fl)
+			tgt_j->pfn_region_enter_printf_va_fl(
+				file, line, us_elapsed_absolute, category,
+				label, repo, fmt, ap);
+
+	tr2tls_push_self(us_now);
+}
+
+void trace2_region_enter_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo)
+{
+	trace2_region_enter_printf_va_fl(file, line, category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(file, line, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(NULL, 0, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Get the elapsed time in the current region before we
+	 * pop it off the stack.  Pop the stack.  And then print
+	 * the perf message at the new (shallower) level so that
+	 * it lines up with the corresponding push/enter.
+	 */
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	tr2tls_pop_self();
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_region_leave_printf_va_fl)
+			tgt_j->pfn_region_leave_printf_va_fl(
+				file, line, us_elapsed_absolute,
+				us_elapsed_region, category, label, repo, fmt,
+				ap);
+}
+
+void trace2_region_leave_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo)
+{
+	trace2_region_leave_printf_va_fl(file, line, category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(file, line, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(NULL, 0, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_data_string_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_data_fl)
+			tgt_j->pfn_data_fl(file, line, us_elapsed_absolute,
+					   us_elapsed_region, category, repo,
+					   key, value);
+}
+
+void trace2_data_intmax_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   intmax_t value)
+{
+	struct strbuf buf_string = STRBUF_INIT;
+
+	if (!trace2_enabled)
+		return;
+
+	strbuf_addf(&buf_string, "%" PRIdMAX, value);
+	trace2_data_string_fl(file, line, category, repo, key, buf_string.buf);
+	strbuf_release(&buf_string);
+}
+
+void trace2_data_json_fl(const char *file, int line, const char *category,
+			 const struct repository *repo, const char *key,
+			 const struct json_writer *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_data_fl)
+			tgt_j->pfn_data_json_fl(file, line, us_elapsed_absolute,
+						us_elapsed_region, category,
+						repo, key, value);
+}
+
+void trace2_printf_va_fl(const char *file, int line, const char *fmt,
+			 va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_printf_va_fl)
+			tgt_j->pfn_printf_va_fl(file, line, us_elapsed_absolute,
+						fmt, ap);
+}
+
+void trace2_printf_fl(const char *file, int line, const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(file, line, fmt, ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_printf(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(NULL, 0, fmt, ap);
+	va_end(ap);
+}
+#endif
diff --git a/trace2.h b/trace2.h
new file mode 100644
index 00000000000000..888531eb08380c
--- /dev/null
+++ b/trace2.h
@@ -0,0 +1,410 @@
+#ifndef TRACE2_H
+#define TRACE2_H
+
+struct child_process;
+struct repository;
+struct json_writer;
+
+/*
+ * The public TRACE2 routines are grouped into the following groups:
+ *
+ * [] trace2_initialize -- initialization.
+ * [] trace2_cmd_*      -- emit command/control messages.
+ * [] trace2_child*     -- emit child start/stop messages.
+ * [] trace2_exec*      -- emit exec start/stop messages.
+ * [] trace2_thread*    -- emit thread start/stop messages.
+ * [] trace2_def*       -- emit definition/parameter mesasges.
+ * [] trace2_region*    -- emit region nesting messages.
+ * [] trace2_data*      -- emit region/thread/repo data messages.
+ * [] trace2_printf*    -- legacy trace[1] messages.
+ */
+
+/*
+ * Initialize the TRACE2 clock and do nothing else, in particular
+ * no mallocs, no system inspection, and no environment inspection.
+ *
+ * This should be called at the very top of main() to capture the
+ * process start time.  This is intended to reduce chicken-n-egg
+ * bootstrap pressure.
+ *
+ * It is safe to call this more than once.  This allows capturing
+ * absolute startup costs on Windows which uses a little trickery
+ * to do setup work before common-main.c:main() is called.
+ *
+ * The main trace2_initialize_fl() may be called a little later
+ * after more infrastructure is established.
+ */
+void trace2_initialize_clock(void);
+
+/*
+ * Initialize TRACE2 tracing facility if any of the builtin TRACE2
+ * targets are enabled in the system config or the environment.
+ * Emits a 'version' event.
+ *
+ * Cleanup/Termination is handled automatically by a registered
+ * atexit() routine.
+ */
+void trace2_initialize_fl(const char *file, int line);
+
+#define trace2_initialize() trace2_initialize_fl(__FILE__, __LINE__)
+
+/*
+ * Return true if trace2 is enabled.
+ */
+int trace2_is_enabled(void);
+
+/*
+ * Emit a 'start' event with the original (unmodified) argv.
+ */
+void trace2_cmd_start_fl(const char *file, int line, const char **argv);
+
+#define trace2_cmd_start(argv) trace2_cmd_start_fl(__FILE__, __LINE__, (argv))
+
+/*
+ * Emit an 'exit' event.
+ *
+ * Write the exit-code that will be passed to exit() or returned
+ * from main().
+ *
+ * Use this prior to actually calling exit().
+ * See "#define exit()" in git-compat-util.h
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+
+#define trace2_cmd_exit(code) (trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
+/*
+ * Emit an 'error' event.
+ *
+ * Write an error message to the TRACE2 targets.
+ */
+void trace2_cmd_error_va_fl(const char *file, int line, const char *fmt,
+			    va_list ap);
+
+#define trace2_cmd_error_va(fmt, ap) \
+	trace2_cmd_error_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+/*
+ * Emit a 'pathname' event with the canonical pathname of the current process
+ * This gives post-processors a simple field to identify the command without
+ * having to parse the argv.  For example, to distinguish invocations from
+ * installed versus debug executables.
+ */
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname);
+
+#define trace2_cmd_path(p) trace2_cmd_path_fl(__FILE__, __LINE__, (p))
+
+/*
+ * Emit a 'cmd_name' event with the canonical name of the command.
+ * This gives post-processors a simple field to identify the command
+ * without having to parse the argv.
+ */
+void trace2_cmd_name_fl(const char *file, int line, const char *name);
+
+#define trace2_cmd_name(v) trace2_cmd_name_fl(__FILE__, __LINE__, (v))
+
+/*
+ * Emit a 'cmd_mode' event to further describe the command being run.
+ * For example, "checkout" can checkout a single file or can checkout a
+ * different branch.  This gives post-processors a simple field to compare
+ * equivalent commands without having to parse the argv.
+ */
+void trace2_cmd_mode_fl(const char *file, int line, const char *mode);
+
+#define trace2_cmd_mode(sv) trace2_cmd_mode_fl(__FILE__, __LINE__, (sv))
+
+/*
+ * Emit an 'alias' expansion event.
+ */
+void trace2_cmd_alias_fl(const char *file, int line, const char *alias,
+			 const char **argv);
+
+#define trace2_cmd_alias(alias, argv) \
+	trace2_cmd_alias_fl(__FILE__, __LINE__, (alias), (argv))
+
+/*
+ * Emit one or more 'def_param' events for "interesting" configuration
+ * settings.
+ *
+ * Use the TR2_SYSENV_CFG_PARAM setting to register a comma-separated
+ * list of patterns configured important.  For example:
+ *     git config --system trace2.configParams 'core.*,remote.*.url'
+ * or:
+ *     GIT_TR2_CONFIG_PARAMS=core.*,remote.*.url"
+ *
+ * Note: this routine does a read-only iteration on the config data
+ * (using read_early_config()), so it must not be called until enough
+ * of the process environment has been established.  This includes the
+ * location of the git and worktree directories, expansion of any "-c"
+ * and "-C" command line options, and etc.
+ */
+void trace2_cmd_list_config_fl(const char *file, int line);
+
+#define trace2_cmd_list_config() trace2_cmd_list_config_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a "def_param" event for the given config key/value pair IF
+ * we consider the key to be "interesting".
+ *
+ * Use this for new/updated config settings created/updated after
+ * trace2_cmd_list_config() is called.
+ */
+void trace2_cmd_set_config_fl(const char *file, int line, const char *key,
+			      const char *value);
+
+#define trace2_cmd_set_config(k, v) \
+	trace2_cmd_set_config_fl(__FILE__, __LINE__, (k), (v))
+
+/*
+ * Emit a 'child_start' event prior to spawning a child process.
+ *
+ * Before calling optionally set "cmd->trace2_child_class" to a string
+ * describing the type of the child process.  For example, "editor" or
+ * "pager".
+ */
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd);
+
+#define trace2_child_start(cmd) trace2_child_start_fl(__FILE__, __LINE__, (cmd))
+
+/*
+ * Emit a 'child_exit' event after the child process completes.
+ */
+void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
+			  int child_exit_code);
+
+#define trace2_child_exit(cmd, code) \
+	trace2_child_exit_fl(__FILE__, __LINE__, (cmd), (code))
+
+/*
+ * Emit an 'exec' event prior to calling one of exec(), execv(),
+ * execvp(), and etc.  On Unix-derived systems, this will be the
+ * last event emitted for the current process, unless the exec
+ * fails.  On Windows, exec() behaves like 'child_start' and a
+ * waitpid(), so additional events may be emitted.
+ *
+ * Returns the "exec_id".
+ */
+int trace2_exec_fl(const char *file, int line, const char *exe,
+		   const char **argv);
+
+#define trace2_exec(exe, argv) trace2_exec_fl(__FILE__, __LINE__, (exe), (argv))
+
+/*
+ * Emit an 'exec_result' when possible.  On Unix-derived systems,
+ * this should be called after exec() returns (which only happens
+ * when there is an error starting the new process).  On Windows,
+ * this should be called after the waitpid().
+ *
+ * The "exec_id" should be the value returned from trace2_exec().
+ */
+void trace2_exec_result_fl(const char *file, int line, int exec_id, int code);
+
+#define trace2_exec_result(id, code) \
+	trace2_exec_result_fl(__FILE__, __LINE__, (id), (code))
+
+/*
+ * Emit a 'thread_start' event.  This must be called from inside the
+ * thread-proc to set up the trace2 TLS data for the thread.
+ *
+ * Thread names should be descriptive, like "preload_index".
+ * Thread names will be decorated with an instance number automatically.
+ */
+void trace2_thread_start_fl(const char *file, int line,
+			    const char *thread_name);
+
+#define trace2_thread_start(thread_name) \
+	trace2_thread_start_fl(__FILE__, __LINE__, (thread_name))
+
+/*
+ * Emit a 'thread_exit' event.  This must be called from inside the
+ * thread-proc to report thread-specific data and cleanup TLS data
+ * for the thread.
+ */
+void trace2_thread_exit_fl(const char *file, int line);
+
+#define trace2_thread_exit() trace2_thread_exit_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a 'param' event.
+ *
+ * Write a "<param> = <value>" pair describing some aspect of the
+ * run such as an important configuration setting or command line
+ * option that significantly changes command behavior.
+ */
+void trace2_def_param_fl(const char *file, int line, const char *param,
+			 const char *value);
+
+#define trace2_def_param(param, value) \
+	trace2_def_param_fl(__FILE__, __LINE__, (param), (value))
+
+/*
+ * Tell trace2 about a newly instantiated repo object and assign
+ * a trace2-repo-id to be used in subsequent activity events.
+ *
+ * Emits a 'worktree' event for this repo instance.
+ */
+void trace2_def_repo_fl(const char *file, int line, struct repository *repo);
+
+#define trace2_def_repo(repo) trace2_def_repo_fl(__FILE__, __LINE__, repo)
+
+/*
+ * Emit a 'region_enter' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Enter a new nesting level on the current thread and remember the
+ * current time.  This controls the indenting of all subsequent events
+ * on this thread.
+ */
+void trace2_region_enter_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo);
+
+#define trace2_region_enter(category, label, repo) \
+	trace2_region_enter_fl(__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_enter_printf_va(category, label, repo, fmt, ap)    \
+	trace2_region_enter_printf_va_fl(__FILE__, __LINE__, (category), \
+					 (label), (repo), (fmt), (ap))
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_enter_printf(category, label, repo, ...)                 \
+	trace2_region_enter_printf_fl(__FILE__, __LINE__, (category), (label), \
+				      (repo), __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (region_enter_printf, 4, 5)))
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...);
+/* clang-format on */
+#endif
+
+/*
+ * Emit a 'region_leave' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Leave current nesting level and report the elapsed time spent
+ * in this nesting level.
+ */
+void trace2_region_leave_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo);
+
+#define trace2_region_leave(category, label, repo) \
+	trace2_region_leave_fl(__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_leave_printf_va(category, label, repo, fmt, ap)    \
+	trace2_region_leave_printf_va_fl(__FILE__, __LINE__, (category), \
+					 (label), (repo), (fmt), (ap))
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_leave_printf(category, label, repo, ...)                 \
+	trace2_region_leave_printf_fl(__FILE__, __LINE__, (category), (label), \
+				      (repo), __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (region_leave_printf, 4, 5)))
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...);
+/* clang-format on */
+#endif
+
+/*
+ * Emit a key-value pair 'data' event of the form <category>.<key> = <value>.
+ * This event implicitly contains information about thread, nesting region,
+ * and optional repo-id.
+ *
+ * On event-based TRACE2 targets, this generates a 'data' event suitable
+ * for post-processing.  On printf-based TRACE2 targets, this is converted
+ * into a fixed-format printf message.
+ */
+void trace2_data_string_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   const char *value);
+
+#define trace2_data_string(category, repo, key, value)                       \
+	trace2_data_string_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			      (value))
+
+void trace2_data_intmax_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   intmax_t value);
+
+#define trace2_data_intmax(category, repo, key, value)                       \
+	trace2_data_intmax_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			      (value))
+
+void trace2_data_json_fl(const char *file, int line, const char *category,
+			 const struct repository *repo, const char *key,
+			 const struct json_writer *jw);
+
+#define trace2_data_json(category, repo, key, value)                       \
+	trace2_data_json_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			    (value))
+
+/*
+ * Emit a 'printf' event.
+ *
+ * Write an arbitrary formatted message to the TRACE2 targets.  These
+ * text messages should be considered as human-readable strings without
+ * any formatting guidelines.  Post-processors may choose to ignore
+ * them.
+ */
+void trace2_printf_va_fl(const char *file, int line, const char *fmt,
+			 va_list ap);
+
+#define trace2_printf_va(fmt, ap) \
+	trace2_printf_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+void trace2_printf_fl(const char *file, int line, const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_printf(...) trace2_printf_fl(__FILE__, __LINE__, __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (printf, 1, 2)))
+void trace2_printf(const char *fmt, ...);
+/* clang-format on */
+#endif
+
+/*
+ * Optional platform-specific code to dump information about the
+ * current and any parent process(es).  This is intended to allow
+ * post-processors to know who spawned this git instance and anything
+ * else that the platform may be able to tell us about the current process.
+ */
+
+enum trace2_process_info_reason {
+	TRACE2_PROCESS_INFO_STARTUP,
+	TRACE2_PROCESS_INFO_EXIT,
+};
+
+#if defined(GIT_WINDOWS_NATIVE)
+void trace2_collect_process_info(enum trace2_process_info_reason reason);
+#else
+#define trace2_collect_process_info(reason) \
+	do {                                \
+	} while (0)
+#endif
+
+#endif /* TRACE2_H */
diff --git a/trace2/tr2_cfg.c b/trace2/tr2_cfg.c
new file mode 100644
index 00000000000000..caa7f06948ab97
--- /dev/null
+++ b/trace2/tr2_cfg.c
@@ -0,0 +1,89 @@
+#include "cache.h"
+#include "config.h"
+#include "trace2/tr2_cfg.h"
+#include "trace2/tr2_sysenv.h"
+
+static struct strbuf **tr2_cfg_patterns;
+static int tr2_cfg_count_patterns;
+static int tr2_cfg_loaded;
+
+/*
+ * Parse a string containing a comma-delimited list of config keys
+ * or wildcard patterns into a list of strbufs.
+ */
+static int tr2_cfg_load_patterns(void)
+{
+	struct strbuf **s;
+	const char *envvar;
+
+	if (tr2_cfg_loaded)
+		return tr2_cfg_count_patterns;
+	tr2_cfg_loaded = 1;
+
+	envvar = tr2_sysenv_get(TR2_SYSENV_CFG_PARAM);
+	if (!envvar || !*envvar)
+		return tr2_cfg_count_patterns;
+
+	tr2_cfg_patterns = strbuf_split_buf(envvar, strlen(envvar), ',', -1);
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+
+		if (buf->len && buf->buf[buf->len - 1] == ',')
+			strbuf_setlen(buf, buf->len - 1);
+		strbuf_trim_trailing_newline(*s);
+		strbuf_trim(*s);
+	}
+
+	tr2_cfg_count_patterns = s - tr2_cfg_patterns;
+	return tr2_cfg_count_patterns;
+}
+
+void tr2_cfg_free_patterns(void)
+{
+	if (tr2_cfg_patterns)
+		strbuf_list_free(tr2_cfg_patterns);
+	tr2_cfg_count_patterns = 0;
+	tr2_cfg_loaded = 0;
+}
+
+struct tr2_cfg_data {
+	const char *file;
+	int line;
+};
+
+/*
+ * See if the given config key matches any of our patterns of interest.
+ */
+static int tr2_cfg_cb(const char *key, const char *value, void *d)
+{
+	struct strbuf **s;
+	struct tr2_cfg_data *data = (struct tr2_cfg_data *)d;
+
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+		int wm = wildmatch(buf->buf, key, WM_CASEFOLD);
+		if (wm == WM_MATCH) {
+			trace2_def_param_fl(data->file, data->line, key, value);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+void tr2_cfg_list_config_fl(const char *file, int line)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		read_early_config(tr2_cfg_cb, &data);
+}
+
+void tr2_cfg_set_fl(const char *file, int line, const char *key,
+		    const char *value)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		tr2_cfg_cb(key, value, &data);
+}
diff --git a/trace2/tr2_cfg.h b/trace2/tr2_cfg.h
new file mode 100644
index 00000000000000..d9c98f64ddf252
--- /dev/null
+++ b/trace2/tr2_cfg.h
@@ -0,0 +1,19 @@
+#ifndef TR2_CFG_H
+#define TR2_CFG_H
+
+/*
+ * Iterate over all config settings and emit 'def_param' events for the
+ * "interesting" ones to TRACE2.
+ */
+void tr2_cfg_list_config_fl(const char *file, int line);
+
+/*
+ * Emit a "def_param" event for the given key/value pair IF we consider
+ * the key to be "interesting".
+ */
+void tr2_cfg_set_fl(const char *file, int line, const char *key,
+		    const char *value);
+
+void tr2_cfg_free_patterns(void);
+
+#endif /* TR2_CFG_H */
diff --git a/trace2/tr2_cmd_name.c b/trace2/tr2_cmd_name.c
new file mode 100644
index 00000000000000..e999592b4c45e4
--- /dev/null
+++ b/trace2/tr2_cmd_name.c
@@ -0,0 +1,30 @@
+#include "cache.h"
+#include "trace2/tr2_cmd_name.h"
+
+#define TR2_ENVVAR_PARENT_NAME "GIT_TR2_PARENT_NAME"
+
+static struct strbuf tr2cmdname_hierarchy = STRBUF_INIT;
+
+void tr2_cmd_name_append_hierarchy(const char *name)
+{
+	const char *parent_name = getenv(TR2_ENVVAR_PARENT_NAME);
+
+	strbuf_reset(&tr2cmdname_hierarchy);
+	if (parent_name && *parent_name) {
+		strbuf_addstr(&tr2cmdname_hierarchy, parent_name);
+		strbuf_addch(&tr2cmdname_hierarchy, '/');
+	}
+	strbuf_addstr(&tr2cmdname_hierarchy, name);
+
+	setenv(TR2_ENVVAR_PARENT_NAME, tr2cmdname_hierarchy.buf, 1);
+}
+
+const char *tr2_cmd_name_get_hierarchy(void)
+{
+	return tr2cmdname_hierarchy.buf;
+}
+
+void tr2_cmd_name_release(void)
+{
+	strbuf_release(&tr2cmdname_hierarchy);
+}
diff --git a/trace2/tr2_cmd_name.h b/trace2/tr2_cmd_name.h
new file mode 100644
index 00000000000000..ab70b67a8e0377
--- /dev/null
+++ b/trace2/tr2_cmd_name.h
@@ -0,0 +1,24 @@
+#ifndef TR2_CMD_NAME_H
+#define TR2_CMD_NAME_H
+
+/*
+ * Append the current command name to the list being maintained
+ * in the environment.
+ *
+ * The hierarchy for a top-level git command is just the current
+ * command name.  For a child git process, the hierarchy includes the
+ * names of the parent processes.
+ *
+ * The hierarchy for the current process will be exported to the
+ * environment and inherited by child processes.
+ */
+void tr2_cmd_name_append_hierarchy(const char *name);
+
+/*
+ * Get the command name hierarchy for the current process.
+ */
+const char *tr2_cmd_name_get_hierarchy(void);
+
+void tr2_cmd_name_release(void);
+
+#endif /* TR2_CMD_NAME_H */
diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
new file mode 100644
index 00000000000000..7d96f33420b389
--- /dev/null
+++ b/trace2/tr2_dst.c
@@ -0,0 +1,254 @@
+#include "cache.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sysenv.h"
+
+/*
+ * If a Trace2 target cannot be opened for writing, we should issue a
+ * warning to stderr, but this is very annoying if the target is a pipe
+ * or socket and beyond the user's control -- especially since every
+ * git command (and sub-command) will print the message.  So we silently
+ * eat these warnings and just discard the trace data.
+ */
+static int tr2_dst_want_warning(void)
+{
+	static int tr2env_dst_debug = -1;
+
+	if (tr2env_dst_debug == -1) {
+		const char *env_value = tr2_sysenv_get(TR2_SYSENV_DST_DEBUG);
+		if (!env_value || !*env_value)
+			tr2env_dst_debug = 0;
+		else
+			tr2env_dst_debug = atoi(env_value) > 0;
+	}
+
+	return tr2env_dst_debug;
+}
+
+void tr2_dst_trace_disable(struct tr2_dst *dst)
+{
+	if (dst->need_close)
+		close(dst->fd);
+	dst->fd = 0;
+	dst->initialized = 1;
+	dst->need_close = 0;
+}
+
+static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value)
+{
+	int fd = open(tgt_value, O_WRONLY | O_APPEND | O_CREAT, 0666);
+	if (fd == -1) {
+		if (tr2_dst_want_warning())
+			warning("trace2: could not open '%s' for '%s' tracing: %s",
+				tgt_value,
+				tr2_sysenv_display_name(dst->sysenv_var),
+				strerror(errno));
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	dst->fd = fd;
+	dst->need_close = 1;
+	dst->initialized = 1;
+
+	return dst->fd;
+}
+
+#ifndef NO_UNIX_SOCKETS
+#define PREFIX_AF_UNIX "af_unix:"
+#define PREFIX_AF_UNIX_STREAM "af_unix:stream:"
+#define PREFIX_AF_UNIX_DGRAM "af_unix:dgram:"
+
+static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd)
+{
+	int fd;
+	struct sockaddr_un sa;
+
+	fd = socket(AF_UNIX, sock_type, 0);
+	if (fd == -1)
+		return errno;
+
+	sa.sun_family = AF_UNIX;
+	strlcpy(sa.sun_path, path, sizeof(sa.sun_path));
+
+	if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
+		int e = errno;
+		close(fd);
+		return e;
+	}
+
+	*out_fd = fd;
+	return 0;
+}
+
+#define TR2_DST_UDS_TRY_STREAM (1 << 0)
+#define TR2_DST_UDS_TRY_DGRAM  (1 << 1)
+
+static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
+					  const char *tgt_value)
+{
+	unsigned int uds_try = 0;
+	int fd;
+	int e;
+	const char *path = NULL;
+
+	/*
+	 * Allow "af_unix:[<type>:]<absolute_path>"
+	 *
+	 * Trace2 always writes complete individual messages (without
+	 * chunking), so we can talk to either DGRAM or STREAM type sockets.
+	 *
+	 * Allow the user to explicitly request the socket type.
+	 *
+	 * If they omit the socket type, try one and then the other.
+	 */
+
+	if (skip_prefix(tgt_value, PREFIX_AF_UNIX_STREAM, &path))
+		uds_try |= TR2_DST_UDS_TRY_STREAM;
+
+	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX_DGRAM, &path))
+		uds_try |= TR2_DST_UDS_TRY_DGRAM;
+
+	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX, &path))
+		uds_try |= TR2_DST_UDS_TRY_STREAM | TR2_DST_UDS_TRY_DGRAM;
+
+	if (!path || !*path) {
+		if (tr2_dst_want_warning())
+			warning("trace2: invalid AF_UNIX value '%s' for '%s' tracing",
+				tgt_value,
+				tr2_sysenv_display_name(dst->sysenv_var));
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	if (!is_absolute_path(path) ||
+	    strlen(path) >= sizeof(((struct sockaddr_un *)0)->sun_path)) {
+		if (tr2_dst_want_warning())
+			warning("trace2: invalid AF_UNIX path '%s' for '%s' tracing",
+				path, tr2_sysenv_display_name(dst->sysenv_var));
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	if (uds_try & TR2_DST_UDS_TRY_STREAM) {
+		e = tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd);
+		if (!e)
+			goto connected;
+		if (e != EPROTOTYPE)
+			goto error;
+	}
+	if (uds_try & TR2_DST_UDS_TRY_DGRAM) {
+		e = tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd);
+		if (!e)
+			goto connected;
+	}
+
+error:
+	if (tr2_dst_want_warning())
+		warning("trace2: could not connect to socket '%s' for '%s' tracing: %s",
+			path, tr2_sysenv_display_name(dst->sysenv_var),
+			strerror(e));
+
+	tr2_dst_trace_disable(dst);
+	return 0;
+
+connected:
+	dst->fd = fd;
+	dst->need_close = 1;
+	dst->initialized = 1;
+
+	return dst->fd;
+}
+#endif
+
+static void tr2_dst_malformed_warning(struct tr2_dst *dst,
+				      const char *tgt_value)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_addf(&buf, "trace2: unknown value for '%s': '%s'",
+		    tr2_sysenv_display_name(dst->sysenv_var), tgt_value);
+	warning("%s", buf.buf);
+
+	strbuf_release(&buf);
+}
+
+int tr2_dst_get_trace_fd(struct tr2_dst *dst)
+{
+	const char *tgt_value;
+
+	/* don't open twice */
+	if (dst->initialized)
+		return dst->fd;
+
+	dst->initialized = 1;
+
+	tgt_value = tr2_sysenv_get(dst->sysenv_var);
+
+	if (!tgt_value || !strcmp(tgt_value, "") || !strcmp(tgt_value, "0") ||
+	    !strcasecmp(tgt_value, "false")) {
+		dst->fd = 0;
+		return dst->fd;
+	}
+
+	if (!strcmp(tgt_value, "1") || !strcasecmp(tgt_value, "true")) {
+		dst->fd = STDERR_FILENO;
+		return dst->fd;
+	}
+
+	if (strlen(tgt_value) == 1 && isdigit(*tgt_value)) {
+		dst->fd = atoi(tgt_value);
+		return dst->fd;
+	}
+
+	if (is_absolute_path(tgt_value))
+		return tr2_dst_try_path(dst, tgt_value);
+
+#ifndef NO_UNIX_SOCKETS
+	if (starts_with(tgt_value, PREFIX_AF_UNIX))
+		return tr2_dst_try_unix_domain_socket(dst, tgt_value);
+#endif
+
+	/* Always warn about malformed values. */
+	tr2_dst_malformed_warning(dst, tgt_value);
+	tr2_dst_trace_disable(dst);
+	return 0;
+}
+
+int tr2_dst_trace_want(struct tr2_dst *dst)
+{
+	return !!tr2_dst_get_trace_fd(dst);
+}
+
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line)
+{
+	int fd = tr2_dst_get_trace_fd(dst);
+
+	strbuf_complete_line(buf_line); /* ensure final NL on buffer */
+
+	/*
+	 * We do not use write_in_full() because we do not want
+	 * a short-write to try again.  We are using O_APPEND mode
+	 * files and the kernel handles the atomic seek+write. If
+	 * another thread or git process is concurrently writing to
+	 * this fd or file, our remainder-write may not be contiguous
+	 * with our initial write of this message.  And that will
+	 * confuse readers.  So just don't bother.
+	 *
+	 * It is assumed that TRACE2 messages are short enough that
+	 * the system can write them in 1 attempt and we won't see
+	 * a short-write.
+	 *
+	 * If we get an IO error, just close the trace dst.
+	 */
+	if (write(fd, buf_line->buf, buf_line->len) >= 0)
+		return;
+
+	if (tr2_dst_want_warning())
+		warning("unable to write trace to '%s': %s",
+			tr2_sysenv_display_name(dst->sysenv_var),
+			strerror(errno));
+	tr2_dst_trace_disable(dst);
+}
diff --git a/trace2/tr2_dst.h b/trace2/tr2_dst.h
new file mode 100644
index 00000000000000..3adf3bac139b1a
--- /dev/null
+++ b/trace2/tr2_dst.h
@@ -0,0 +1,37 @@
+#ifndef TR2_DST_H
+#define TR2_DST_H
+
+struct strbuf;
+#include "trace2/tr2_sysenv.h"
+
+struct tr2_dst {
+	enum tr2_sysenv_variable sysenv_var;
+	int fd;
+	unsigned int initialized : 1;
+	unsigned int need_close : 1;
+};
+
+/*
+ * Disable TRACE2 on the destination.  In TRACE2 a destination (DST)
+ * wraps a file descriptor; it is associated with a TARGET which
+ * defines the formatting.
+ */
+void tr2_dst_trace_disable(struct tr2_dst *dst);
+
+/*
+ * Return the file descriptor for the DST.
+ * If 0, the dst is closed or disabled.
+ */
+int tr2_dst_get_trace_fd(struct tr2_dst *dst);
+
+/*
+ * Return true if the DST is opened for writing.
+ */
+int tr2_dst_trace_want(struct tr2_dst *dst);
+
+/*
+ * Write a single line/message to the trace file.
+ */
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line);
+
+#endif /* TR2_DST_H */
diff --git a/trace2/tr2_sid.c b/trace2/tr2_sid.c
new file mode 100644
index 00000000000000..50470954783672
--- /dev/null
+++ b/trace2/tr2_sid.c
@@ -0,0 +1,112 @@
+#include "cache.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_sid.h"
+
+#define TR2_ENVVAR_PARENT_SID "GIT_TR2_PARENT_SID"
+
+static struct strbuf tr2sid_buf = STRBUF_INIT;
+static int tr2sid_nr_git_parents;
+
+/*
+ * Compute the final component of the SID representing the current process.
+ * This should uniquely identify the process and be a valid filename (to
+ * allow writing trace2 data to per-process files).  It should also be fixed
+ * length for possible use as a database key.
+ *
+ * "<yyyymmdd>T<hhmmss>.<fraction>Z-<host>-<process>"
+ *
+ * where <host> is a 9 character string:
+ *    "H<first_8_chars_of_sha1_of_hostname>"
+ *    "Localhost" when no hostname.
+ *
+ * where <process> is a 9 character string containing the least signifcant
+ * 32 bits in the process-id.
+ *    "P<pid>"
+ * (This is an abribrary choice.  On most systems pid_t is a 32 bit value,
+ * so limit doesn't matter.  On larger systems, a truncated value is fine
+ * for our purposes here.)
+ */
+static void tr2_sid_append_my_sid_component(void)
+{
+	const struct git_hash_algo *algo = &hash_algos[GIT_HASH_SHA1];
+	struct tr2_tbuf tb_now;
+	git_hash_ctx ctx;
+	pid_t pid = getpid();
+	unsigned char hash[GIT_MAX_RAWSZ + 1];
+	char hex[GIT_MAX_HEXSZ + 1];
+	char hostname[HOST_NAME_MAX + 1];
+
+	tr2_tbuf_utc_datetime(&tb_now);
+	strbuf_addstr(&tr2sid_buf, tb_now.buf);
+
+	strbuf_addch(&tr2sid_buf, '-');
+	if (xgethostname(hostname, sizeof(hostname)))
+		strbuf_add(&tr2sid_buf, "Localhost", 9);
+	else {
+		algo->init_fn(&ctx);
+		algo->update_fn(&ctx, hostname, strlen(hostname));
+		algo->final_fn(hash, &ctx);
+		hash_to_hex_algop_r(hex, hash, algo);
+		strbuf_addch(&tr2sid_buf, 'H');
+		strbuf_add(&tr2sid_buf, hex, 8);
+	}
+
+	strbuf_addf(&tr2sid_buf, "-P%08"PRIx32, (uint32_t)pid);
+}
+
+/*
+ * Compute a "unique" session id (SID) for the current process.  This allows
+ * all events from this process to have a single label (much like a PID).
+ *
+ * Export this into our environment so that all child processes inherit it.
+ *
+ * If we were started by another git instance, use our parent's SID as a
+ * prefix.  (This lets us track parent/child relationships even if there
+ * is an intermediate shell process.)
+ *
+ * Additionally, count the number of nested git processes.
+ */
+static void tr2_sid_compute(void)
+{
+	const char *parent_sid;
+
+	if (tr2sid_buf.len)
+		return;
+
+	parent_sid = getenv(TR2_ENVVAR_PARENT_SID);
+	if (parent_sid && *parent_sid) {
+		const char *p;
+		for (p = parent_sid; *p; p++)
+			if (*p == '/')
+				tr2sid_nr_git_parents++;
+
+		strbuf_addstr(&tr2sid_buf, parent_sid);
+		strbuf_addch(&tr2sid_buf, '/');
+		tr2sid_nr_git_parents++;
+	}
+
+	tr2_sid_append_my_sid_component();
+
+	setenv(TR2_ENVVAR_PARENT_SID, tr2sid_buf.buf, 1);
+}
+
+const char *tr2_sid_get(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_buf.buf;
+}
+
+int tr2_sid_depth(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_nr_git_parents;
+}
+
+void tr2_sid_release(void)
+{
+	strbuf_release(&tr2sid_buf);
+}
diff --git a/trace2/tr2_sid.h b/trace2/tr2_sid.h
new file mode 100644
index 00000000000000..9bef3217081a7e
--- /dev/null
+++ b/trace2/tr2_sid.h
@@ -0,0 +1,18 @@
+#ifndef TR2_SID_H
+#define TR2_SID_H
+
+/*
+ * Get our session id. Compute if necessary.
+ */
+const char *tr2_sid_get(void);
+
+/*
+ * Get our process depth.  A top-level git process invoked from the
+ * command line will have depth=0.  A child git process will have
+ * depth=1 and so on.
+ */
+int tr2_sid_depth(void);
+
+void tr2_sid_release(void);
+
+#endif /* TR2_SID_H */
diff --git a/trace2/tr2_sysenv.c b/trace2/tr2_sysenv.c
new file mode 100644
index 00000000000000..9025b863034f5a
--- /dev/null
+++ b/trace2/tr2_sysenv.c
@@ -0,0 +1,127 @@
+#include "cache.h"
+#include "config.h"
+#include "dir.h"
+#include "tr2_sysenv.h"
+
+/*
+ * Each entry represents a trace2 setting.
+ * See Documentation/technical/api-trace2.txt
+ */
+struct tr2_sysenv_entry {
+	const char *env_var_name;
+	const char *git_config_name;
+
+	char *value;
+	unsigned int getenv_called : 1;
+};
+
+/*
+ * This table must match "enum tr2_sysenv_variable" in tr2_sysenv.h.
+ *
+ * The strings in this table are constant and must match the published
+ * config and environment variable names as described in the documentation.
+ *
+ * We do not define entries for the GIT_TR2_PARENT_* environment
+ * variables because they are transient and used to pass information
+ * from parent to child git processes, rather than settings.
+ */
+/* clang-format off */
+static struct tr2_sysenv_entry tr2_sysenv_settings[] = {
+	[TR2_SYSENV_CFG_PARAM]     = { "GIT_TR2_CONFIG_PARAMS",
+				       "trace2.configparams" },
+
+	[TR2_SYSENV_DST_DEBUG]     = { "GIT_TR2_DST_DEBUG",
+				       "trace2.destinationdebug" },
+
+	[TR2_SYSENV_NORMAL]        = { "GIT_TR2",
+				       "trace2.normaltarget" },
+	[TR2_SYSENV_NORMAL_BRIEF]  = { "GIT_TR2_BRIEF",
+				       "trace2.normalbrief" },
+
+	[TR2_SYSENV_EVENT]         = { "GIT_TR2_EVENT",
+				       "trace2.eventtarget" },
+	[TR2_SYSENV_EVENT_BRIEF]   = { "GIT_TR2_EVENT_BRIEF",
+				       "trace2.eventbrief" },
+	[TR2_SYSENV_EVENT_NESTING] = { "GIT_TR2_EVENT_NESTING",
+				       "trace2.eventnesting" },
+
+	[TR2_SYSENV_PERF]          = { "GIT_TR2_PERF",
+				       "trace2.perftarget" },
+	[TR2_SYSENV_PERF_BRIEF]    = { "GIT_TR2_PERF_BRIEF",
+				       "trace2.perfbrief" },
+};
+/* clang-format on */
+
+static int tr2_sysenv_cb(const char *key, const char *value, void *d)
+{
+	int k;
+
+	if (!starts_with(key, "trace2."))
+		return 0;
+
+	for (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++) {
+		if (!strcmp(key, tr2_sysenv_settings[k].git_config_name)) {
+			free(tr2_sysenv_settings[k].value);
+			tr2_sysenv_settings[k].value = xstrdup(value);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Load Trace2 settings from the system config (usually "/etc/gitconfig"
+ * unless we were built with a runtime-prefix).  These are intended to
+ * define the default values for Trace2 as requested by the administrator.
+ *
+ * Then override with the Trace2 settings from the global config.
+ */
+void tr2_sysenv_load(void)
+{
+	if (ARRAY_SIZE(tr2_sysenv_settings) != TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_settings size is wrong");
+
+	read_very_early_config(tr2_sysenv_cb, NULL);
+}
+
+/*
+ * Return the value for the requested Trace2 setting from these sources:
+ * the system config, the global config, and the environment.
+ */
+const char *tr2_sysenv_get(enum tr2_sysenv_variable var)
+{
+	if (var >= TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_get invalid var '%d'", var);
+
+	if (!tr2_sysenv_settings[var].getenv_called) {
+		const char *v = getenv(tr2_sysenv_settings[var].env_var_name);
+		if (v && *v) {
+			free(tr2_sysenv_settings[var].value);
+			tr2_sysenv_settings[var].value = xstrdup(v);
+		}
+		tr2_sysenv_settings[var].getenv_called = 1;
+	}
+
+	return tr2_sysenv_settings[var].value;
+}
+
+/*
+ * Return a friendly name for this setting that is suitable for printing
+ * in an error messages.
+ */
+const char *tr2_sysenv_display_name(enum tr2_sysenv_variable var)
+{
+	if (var >= TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_get invalid var '%d'", var);
+
+	return tr2_sysenv_settings[var].env_var_name;
+}
+
+void tr2_sysenv_release(void)
+{
+	int k;
+
+	for (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++)
+		free(tr2_sysenv_settings[k].value);
+}
diff --git a/trace2/tr2_sysenv.h b/trace2/tr2_sysenv.h
new file mode 100644
index 00000000000000..369b20bd87f589
--- /dev/null
+++ b/trace2/tr2_sysenv.h
@@ -0,0 +1,36 @@
+#ifndef TR2_SYSENV_H
+#define TR2_SYSENV_H
+
+/*
+ * The Trace2 settings that can be loaded from /etc/gitconfig
+ * and/or user environment variables.
+ *
+ * Note that this set does not contain any of the transient
+ * environment variables used to pass information from parent
+ * to child git processes, such "GIT_TR2_PARENT_SID".
+ */
+enum tr2_sysenv_variable {
+	TR2_SYSENV_CFG_PARAM = 0,
+
+	TR2_SYSENV_DST_DEBUG,
+
+	TR2_SYSENV_NORMAL,
+	TR2_SYSENV_NORMAL_BRIEF,
+
+	TR2_SYSENV_EVENT,
+	TR2_SYSENV_EVENT_BRIEF,
+	TR2_SYSENV_EVENT_NESTING,
+
+	TR2_SYSENV_PERF,
+	TR2_SYSENV_PERF_BRIEF,
+
+	TR2_SYSENV_MUST_BE_LAST
+};
+
+void tr2_sysenv_load(void);
+
+const char *tr2_sysenv_get(enum tr2_sysenv_variable);
+const char *tr2_sysenv_display_name(enum tr2_sysenv_variable var);
+void tr2_sysenv_release(void);
+
+#endif /* TR2_SYSENV_H */
diff --git a/trace2/tr2_tbuf.c b/trace2/tr2_tbuf.c
new file mode 100644
index 00000000000000..2498482d9ad82a
--- /dev/null
+++ b/trace2/tr2_tbuf.c
@@ -0,0 +1,47 @@
+#include "cache.h"
+#include "tr2_tbuf.h"
+
+void tr2_tbuf_local_time(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	localtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf), "%02d:%02d:%02d.%06ld", tm.tm_hour,
+		  tm.tm_min, tm.tm_sec, (long)tv.tv_usec);
+}
+
+void tr2_tbuf_utc_datetime_extended(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	gmtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf),
+		  "%4d-%02d-%02dT%02d:%02d:%02d.%06ldZ", tm.tm_year + 1900,
+		  tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec,
+		  (long)tv.tv_usec);
+}
+
+void tr2_tbuf_utc_datetime(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	gmtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf), "%4d%02d%02dT%02d%02d%02d.%06ldZ",
+		  tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour,
+		  tm.tm_min, tm.tm_sec, (long)tv.tv_usec);
+}
diff --git a/trace2/tr2_tbuf.h b/trace2/tr2_tbuf.h
new file mode 100644
index 00000000000000..fa853d8f4211b5
--- /dev/null
+++ b/trace2/tr2_tbuf.h
@@ -0,0 +1,24 @@
+#ifndef TR2_TBUF_H
+#define TR2_TBUF_H
+
+/*
+ * A simple wrapper around a fixed buffer to avoid C syntax
+ * quirks and the need to pass around an additional size_t
+ * argument.
+ */
+struct tr2_tbuf {
+	char buf[32];
+};
+
+/*
+ * Fill buffer with formatted local time string.
+ */
+void tr2_tbuf_local_time(struct tr2_tbuf *tb);
+
+/*
+ * Fill buffer with formatted UTC datatime string.
+ */
+void tr2_tbuf_utc_datetime_extended(struct tr2_tbuf *tb);
+void tr2_tbuf_utc_datetime(struct tr2_tbuf *tb);
+
+#endif /* TR2_TBUF_H */
diff --git a/trace2/tr2_tgt.h b/trace2/tr2_tgt.h
new file mode 100644
index 00000000000000..7b904692123e28
--- /dev/null
+++ b/trace2/tr2_tgt.h
@@ -0,0 +1,134 @@
+#ifndef TR2_TGT_H
+#define TR2_TGT_H
+
+struct child_process;
+struct repository;
+struct json_writer;
+
+/*
+ * Function prototypes for a TRACE2 "target" vtable.
+ */
+
+typedef int(tr2_tgt_init_t)(void);
+typedef void(tr2_tgt_term_t)(void);
+
+typedef void(tr2_tgt_evt_version_fl_t)(const char *file, int line);
+
+typedef void(tr2_tgt_evt_start_fl_t)(const char *file, int line,
+				     uint64_t us_elapsed_absolute,
+				     const char **argv);
+typedef void(tr2_tgt_evt_exit_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute, int code);
+typedef void(tr2_tgt_evt_signal_t)(uint64_t us_elapsed_absolute, int signo);
+typedef void(tr2_tgt_evt_atexit_t)(uint64_t us_elapsed_absolute, int code);
+
+typedef void(tr2_tgt_evt_error_va_fl_t)(const char *file, int line,
+					const char *fmt, va_list ap);
+
+typedef void(tr2_tgt_evt_command_path_fl_t)(const char *file, int line,
+					    const char *command_path);
+typedef void(tr2_tgt_evt_command_name_fl_t)(const char *file, int line,
+					    const char *name,
+					    const char *hierarchy);
+typedef void(tr2_tgt_evt_command_mode_fl_t)(const char *file, int line,
+					    const char *mode);
+
+typedef void(tr2_tgt_evt_alias_fl_t)(const char *file, int line,
+				     const char *alias, const char **argv);
+
+typedef void(tr2_tgt_evt_child_start_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   const struct child_process *cmd);
+typedef void(tr2_tgt_evt_child_exit_fl_t)(const char *file, int line,
+					  uint64_t us_elapsed_absolute, int cid,
+					  int pid, int code,
+					  uint64_t us_elapsed_child);
+
+typedef void(tr2_tgt_evt_thread_start_fl_t)(const char *file, int line,
+					    uint64_t us_elapsed_absolute);
+typedef void(tr2_tgt_evt_thread_exit_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   uint64_t us_elapsed_thread);
+
+typedef void(tr2_tgt_evt_exec_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute, int exec_id,
+				    const char *exe, const char **argv);
+typedef void(tr2_tgt_evt_exec_result_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   int exec_id, int code);
+
+typedef void(tr2_tgt_evt_param_fl_t)(const char *file, int line,
+				     const char *param, const char *value);
+
+typedef void(tr2_tgt_evt_repo_fl_t)(const char *file, int line,
+				    const struct repository *repo);
+
+typedef void(tr2_tgt_evt_region_enter_printf_va_fl_t)(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	const char *category, const char *label, const struct repository *repo,
+	const char *fmt, va_list ap);
+typedef void(tr2_tgt_evt_region_leave_printf_va_fl_t)(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap);
+
+typedef void(tr2_tgt_evt_data_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute,
+				    uint64_t us_elapsed_region,
+				    const char *category,
+				    const struct repository *repo,
+				    const char *key, const char *value);
+typedef void(tr2_tgt_evt_data_json_fl_t)(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 uint64_t us_elapsed_region,
+					 const char *category,
+					 const struct repository *repo,
+					 const char *key,
+					 const struct json_writer *value);
+
+typedef void(tr2_tgt_evt_printf_va_fl_t)(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *fmt, va_list ap);
+
+/*
+ * "vtable" for a TRACE2 target.  Use NULL if a target does not want
+ * to emit that message.
+ */
+/* clang-format off */
+struct tr2_tgt {
+	struct tr2_dst                          *pdst;
+
+	tr2_tgt_init_t                          *pfn_init;
+	tr2_tgt_term_t                          *pfn_term;
+
+	tr2_tgt_evt_version_fl_t                *pfn_version_fl;
+	tr2_tgt_evt_start_fl_t                  *pfn_start_fl;
+	tr2_tgt_evt_exit_fl_t                   *pfn_exit_fl;
+	tr2_tgt_evt_signal_t                    *pfn_signal;
+	tr2_tgt_evt_atexit_t                    *pfn_atexit;
+	tr2_tgt_evt_error_va_fl_t               *pfn_error_va_fl;
+	tr2_tgt_evt_command_path_fl_t           *pfn_command_path_fl;
+	tr2_tgt_evt_command_name_fl_t           *pfn_command_name_fl;
+	tr2_tgt_evt_command_mode_fl_t           *pfn_command_mode_fl;
+	tr2_tgt_evt_alias_fl_t                  *pfn_alias_fl;
+	tr2_tgt_evt_child_start_fl_t            *pfn_child_start_fl;
+	tr2_tgt_evt_child_exit_fl_t             *pfn_child_exit_fl;
+	tr2_tgt_evt_thread_start_fl_t           *pfn_thread_start_fl;
+	tr2_tgt_evt_thread_exit_fl_t            *pfn_thread_exit_fl;
+	tr2_tgt_evt_exec_fl_t                   *pfn_exec_fl;
+	tr2_tgt_evt_exec_result_fl_t            *pfn_exec_result_fl;
+	tr2_tgt_evt_param_fl_t                  *pfn_param_fl;
+	tr2_tgt_evt_repo_fl_t                   *pfn_repo_fl;
+	tr2_tgt_evt_region_enter_printf_va_fl_t *pfn_region_enter_printf_va_fl;
+	tr2_tgt_evt_region_leave_printf_va_fl_t *pfn_region_leave_printf_va_fl;
+	tr2_tgt_evt_data_fl_t                   *pfn_data_fl;
+	tr2_tgt_evt_data_json_fl_t              *pfn_data_json_fl;
+	tr2_tgt_evt_printf_va_fl_t              *pfn_printf_va_fl;
+};
+/* clang-format on */
+
+extern struct tr2_tgt tr2_tgt_event;
+extern struct tr2_tgt tr2_tgt_normal;
+extern struct tr2_tgt tr2_tgt_perf;
+
+#endif /* TR2_TGT_H */
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
new file mode 100644
index 00000000000000..2c97cf54be95e2
--- /dev/null
+++ b/trace2/tr2_tgt_event.c
@@ -0,0 +1,591 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "run-command.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_sysenv.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_event = { TR2_SYSENV_EVENT, 0, 0, 0 };
+
+/*
+ * The version number of the JSON data generated by the EVENT target
+ * in this source file.  Update this if you make a significant change
+ * to the JSON fields or message structure.  You probably do not need
+ * to update this if you just add another call to one of the existing
+ * TRACE2 API methods.
+ */
+#define TR2_EVENT_VERSION "1"
+
+/*
+ * Region nesting limit for messages written to the event target.
+ *
+ * The "region_enter" and "region_leave" messages (especially recursive
+ * messages such as those produced while diving the worktree or index)
+ * are primarily intended for the performance target during debugging.
+ *
+ * Some of the outer-most messages, however, may be of interest to the
+ * event target.  Use the TR2_SYSENV_EVENT_NESTING setting to increase
+ * region details in the event target.
+ */
+static int tr2env_event_max_nesting_levels = 2;
+
+/*
+ * Use the TR2_SYSENV_EVENT_BRIEF to omit the <time>, <file>, and
+ * <line> fields from most events.
+ */
+static int tr2env_event_be_brief;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_event);
+	int max_nesting;
+	int want_brief;
+	const char *nesting;
+	const char *brief;
+
+	if (!want)
+		return want;
+
+	nesting = tr2_sysenv_get(TR2_SYSENV_EVENT_NESTING);
+	if (nesting && *nesting && ((max_nesting = atoi(nesting)) > 0))
+		tr2env_event_max_nesting_levels = max_nesting;
+
+	brief = tr2_sysenv_get(TR2_SYSENV_EVENT_BRIEF);
+	if (brief && *brief &&
+	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
+		tr2env_event_be_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_event);
+}
+
+/*
+ * Append common key-value pairs to the currently open JSON object.
+ *     "event:"<event_name>"
+ *      "sid":"<sid>"
+ *   "thread":"<thread_name>"
+ *     "time":"<time>"
+ *     "file":"<filename>"
+ *     "line":<line_number>
+ *     "repo":<repo_id>
+ */
+static void event_fmt_prepare(const char *event_name, const char *file,
+			      int line, const struct repository *repo,
+			      struct json_writer *jw)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct tr2_tbuf tb_now;
+
+	jw_object_string(jw, "event", event_name);
+	jw_object_string(jw, "sid", tr2_sid_get());
+	jw_object_string(jw, "thread", ctx->thread_name.buf);
+
+	/*
+	 * In brief mode, only emit <time> on these 2 event types.
+	 */
+	if (!tr2env_event_be_brief || !strcmp(event_name, "version") ||
+	    !strcmp(event_name, "atexit")) {
+		tr2_tbuf_utc_datetime_extended(&tb_now);
+		jw_object_string(jw, "time", tb_now.buf);
+	}
+
+	if (!tr2env_event_be_brief && file && *file) {
+		jw_object_string(jw, "file", file);
+		jw_object_intmax(jw, "line", line);
+	}
+
+	if (repo)
+		jw_object_intmax(jw, "repo", repo->trace2_repo_id);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "evt", TR2_EVENT_VERSION);
+	jw_object_string(&jw, "exe", git_version_string);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_start_fl(const char *file, int line,
+			uint64_t us_elapsed_absolute, const char **argv)
+{
+	const char *event_name = "start";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	const char *event_name = "exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "signo", signo);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void maybe_add_string_va(struct json_writer *jw, const char *field_name,
+				const char *fmt, va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+		struct strbuf buf = STRBUF_INIT;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(&buf, fmt, copy_ap);
+		va_end(copy_ap);
+
+		jw_object_string(jw, field_name, buf.buf);
+		strbuf_release(&buf);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		jw_object_string(jw, field_name, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	const char *event_name = "error";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	maybe_add_string_va(&jw, "msg", fmt, ap);
+	/*
+	 * Also emit the format string as a field in case
+	 * post-processors want to aggregate common error
+	 * messages by type without argument fields (such
+	 * as pathnames or branch names) cluttering it up.
+	 */
+	if (fmt && *fmt)
+		jw_object_string(&jw, "fmt", fmt);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "path", pathname);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	const char *event_name = "cmd_name";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "name", name);
+	if (hierarchy && *hierarchy)
+		jw_object_string(&jw, "hierarchy", hierarchy);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	const char *event_name = "cmd_mode";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "name", mode);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	const char *event_name = "alias";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "alias", alias);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cmd->trace2_child_id);
+	if (cmd->trace2_hook_name) {
+		jw_object_string(&jw, "child_class", "hook");
+		jw_object_string(&jw, "hook_name", cmd->trace2_hook_name);
+	} else {
+		const char *child_class =
+			cmd->trace2_child_class ? cmd->trace2_child_class : "?";
+		jw_object_string(&jw, "child_class", child_class);
+	}
+	if (cmd->dir)
+		jw_object_string(&jw, "cd", cmd->dir);
+	jw_object_bool(&jw, "use_shell", cmd->use_shell);
+	jw_object_inline_begin_array(&jw, "argv");
+	if (cmd->git_cmd)
+		jw_array_string(&jw, "git");
+	jw_array_argv(&jw, cmd->argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_child / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cid);
+	jw_object_intmax(&jw, "pid", pid);
+	jw_object_intmax(&jw, "code", code);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+
+	jw_release(&jw);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+			       uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_thread / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "exec_id", exec_id);
+	if (exe)
+		jw_object_string(&jw, "exe", exe);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	const char *event_name = "exec_result";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "exec_id", exec_id);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	const char *event_name = "def_param";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "param", param);
+	jw_object_string(&jw, "value", value);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, repo, &jw);
+	jw_object_string(&jw, "worktree", repo->worktree);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_max_nesting_levels) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_region_leave_printf_va_fl(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_max_nesting_levels) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_data_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region, const char *category,
+		       const struct repository *repo, const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_max_nesting_levels) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_abs = (double)us_elapsed_absolute / 1000000.0;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_abs", 6, t_abs);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		jw_object_string(&jw, "category", category);
+		jw_object_string(&jw, "key", key);
+		jw_object_string(&jw, "value", value);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_data_json_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    uint64_t us_elapsed_region, const char *category,
+			    const struct repository *repo, const char *key,
+			    const struct json_writer *value)
+{
+	const char *event_name = "data_json";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_max_nesting_levels) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_abs = (double)us_elapsed_absolute / 1000000.0;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_abs", 6, t_abs);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		jw_object_string(&jw, "category", category);
+		jw_object_string(&jw, "key", key);
+		jw_object_sub_jw(&jw, "value", value);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+struct tr2_tgt tr2_tgt_event = {
+	&tr2dst_event,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	fn_data_json_fl,
+	NULL, /* printf */
+};
diff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c
new file mode 100644
index 00000000000000..1ce6f978631930
--- /dev/null
+++ b/trace2/tr2_tgt_normal.c
@@ -0,0 +1,324 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sysenv.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_normal = { TR2_SYSENV_NORMAL, 0, 0, 0 };
+
+/*
+ * Use the TR2_SYSENV_NORMAL_BRIEF setting to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin normal target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+static int tr2env_normal_be_brief;
+
+#define TR2FMT_NORMAL_FL_WIDTH (50)
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_normal);
+	int want_brief;
+	const char *brief;
+
+	if (!want)
+		return want;
+
+	brief = tr2_sysenv_get(TR2_SYSENV_NORMAL_BRIEF);
+	if (brief && *brief &&
+	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
+		tr2env_normal_be_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_normal);
+}
+
+static void normal_fmt_prepare(const char *file, int line, struct strbuf *buf)
+{
+	strbuf_setlen(buf, 0);
+
+	if (!tr2env_normal_be_brief) {
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_local_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_NORMAL_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+	}
+}
+
+static void normal_io_write_fl(const char *file, int line,
+			       const struct strbuf *buf_payload)
+{
+	struct strbuf buf_line = STRBUF_INIT;
+
+	normal_fmt_prepare(file, line, &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_normal, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "version %s", git_version_string);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line,
+			uint64_t us_elapsed_absolute, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "start ");
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "exit elapsed:%.6f code:%d", elapsed, code);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "signal elapsed:%.6f code:%d", elapsed,
+		    signo);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "atexit elapsed:%.6f code:%d", elapsed, code);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
+				   va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "error ");
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_path %s", pathname);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_name %s", name);
+	if (hierarchy && *hierarchy)
+		strbuf_addf(&buf_payload, " (%s)", hierarchy);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_mode %s", mode);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias %s ->", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "child_start[%d] ", cmd->trace2_child_id);
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+		strbuf_addstr(&buf_payload, "; ");
+	}
+
+	/*
+	 * TODO if (cmd->env) { Consider dumping changes to environment. }
+	 * See trace_add_env() in run-command.c as used by original trace.c
+	 */
+
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, "git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_child / 1000000.0;
+
+	strbuf_addf(&buf_payload, "child_exit[%d] pid:%d code:%d elapsed:%.6f",
+		    cid, pid, code, elapsed);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "exec[%d] ", exec_id);
+	if (exe)
+		strbuf_addstr(&buf_payload, exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "exec_result[%d] code:%d", exec_id, code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "def_param %s=%s", param, value);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree ");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute, const char *fmt,
+			    va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_normal = {
+	&tr2dst_normal,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	NULL, /* thread_start */
+	NULL, /* thread_exit */
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	NULL, /* region_enter */
+	NULL, /* region_leave */
+	NULL, /* data */
+	NULL, /* data_json */
+	fn_printf_va_fl,
+};
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
new file mode 100644
index 00000000000000..328d2234bddf04
--- /dev/null
+++ b/trace2/tr2_tgt_perf.c
@@ -0,0 +1,535 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "json-writer.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_sysenv.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_perf = { TR2_SYSENV_PERF, 0, 0, 0 };
+
+/*
+ * Use TR2_SYSENV_PERF_BRIEF to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin performance target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+static int tr2env_perf_be_brief;
+
+#define TR2FMT_PERF_FL_WIDTH (50)
+#define TR2FMT_PERF_MAX_EVENT_NAME (12)
+#define TR2FMT_PERF_REPO_WIDTH (4)
+#define TR2FMT_PERF_CATEGORY_WIDTH (10)
+
+#define TR2_DOTS_BUFFER_SIZE (100)
+#define TR2_INDENT (2)
+#define TR2_INDENT_LENGTH(ctx) (((ctx)->nr_open_regions - 1) * TR2_INDENT)
+
+static struct strbuf dots = STRBUF_INIT;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_perf);
+	int want_brief;
+	const char *brief;
+
+	if (!want)
+		return want;
+
+	strbuf_addchars(&dots, '.', TR2_DOTS_BUFFER_SIZE);
+
+	brief = tr2_sysenv_get(TR2_SYSENV_PERF_BRIEF);
+	if (brief && *brief &&
+	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
+		tr2env_perf_be_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_perf);
+
+	strbuf_release(&dots);
+}
+
+/*
+ * Format trace line prefix in human-readable classic format for
+ * the performance target:
+ *     "[<time> [<file>:<line>] <bar>] <nr_parents> <bar>
+ *         <thread_name> <bar> <event_name> <bar> [<repo>] <bar>
+ *         [<elapsed_absolute>] [<elapsed_relative>] <bar>
+ *         [<category>] <bar> [<dots>] "
+ */
+static void perf_fmt_prepare(const char *event_name,
+			     struct tr2tls_thread_ctx *ctx, const char *file,
+			     int line, const struct repository *repo,
+			     uint64_t *p_us_elapsed_absolute,
+			     uint64_t *p_us_elapsed_relative,
+			     const char *category, struct strbuf *buf)
+{
+	int len;
+
+	strbuf_setlen(buf, 0);
+
+	if (!tr2env_perf_be_brief) {
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_local_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_PERF_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+
+		strbuf_addstr(buf, "| ");
+	}
+
+	strbuf_addf(buf, "d%d | ", tr2_sid_depth());
+	strbuf_addf(buf, "%-*s | %-*s | ", TR2_MAX_THREAD_NAME,
+		    ctx->thread_name.buf, TR2FMT_PERF_MAX_EVENT_NAME,
+		    event_name);
+
+	len = buf->len + TR2FMT_PERF_REPO_WIDTH;
+	if (repo)
+		strbuf_addf(buf, "r%d ", repo->trace2_repo_id);
+	while (buf->len < len)
+		strbuf_addch(buf, ' ');
+	strbuf_addstr(buf, "| ");
+
+	if (p_us_elapsed_absolute)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_absolute)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+
+	if (p_us_elapsed_relative)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_relative)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+
+	strbuf_addf(buf, "%-*s | ", TR2FMT_PERF_CATEGORY_WIDTH,
+		    (category ? category : ""));
+
+	if (ctx->nr_open_regions > 0) {
+		int len_indent = TR2_INDENT_LENGTH(ctx);
+		while (len_indent > dots.len) {
+			strbuf_addbuf(buf, &dots);
+			len_indent -= dots.len;
+		}
+		strbuf_addf(buf, "%.*s", len_indent, dots.buf);
+	}
+}
+
+static void perf_io_write_fl(const char *file, int line, const char *event_name,
+			     const struct repository *repo,
+			     uint64_t *p_us_elapsed_absolute,
+			     uint64_t *p_us_elapsed_relative,
+			     const char *category,
+			     const struct strbuf *buf_payload)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct strbuf buf_line = STRBUF_INIT;
+
+	perf_fmt_prepare(event_name, ctx, file, line, repo,
+			 p_us_elapsed_absolute, p_us_elapsed_relative, category,
+			 &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_perf, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, git_version_string);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line,
+			uint64_t us_elapsed_absolute, const char **argv)
+{
+	const char *event_name = "start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	const char *event_name = "exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "signo:%d", signo);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
+				   va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	const char *event_name = "error";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, pathname);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	const char *event_name = "cmd_name";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, name);
+	if (hierarchy && *hierarchy)
+		strbuf_addf(&buf_payload, " (%s)", hierarchy);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	const char *event_name = "cmd_mode";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, mode);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	const char *event_name = "alias";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias:%s argv:", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (cmd->trace2_hook_name) {
+		strbuf_addf(&buf_payload, "[ch%d] class:hook hook:%s",
+			    cmd->trace2_child_id, cmd->trace2_hook_name);
+	} else {
+		const char *child_class =
+			cmd->trace2_child_class ? cmd->trace2_child_class : "?";
+		strbuf_addf(&buf_payload, "[ch%d] class:%s",
+			    cmd->trace2_child_id, child_class);
+	}
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd:");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+	}
+
+	strbuf_addstr(&buf_payload, " argv:");
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, " git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "[ch%d] pid:%d code:%d", cid, pid, code);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 &us_elapsed_child, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+			       uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 &us_elapsed_thread, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "id:%d ", exec_id);
+	strbuf_addstr(&buf_payload, "argv:");
+	if (exe)
+		strbuf_addf(&buf_payload, " %s", exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	const char *event_name = "exec_result";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "id:%d code:%d", exec_id, code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	const char *event_name = "def_param";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", param, value);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree:");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+
+	perf_io_write_fl(file, line, event_name, repo, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 NULL, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_leave_printf_va_fl(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_data_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region, const char *category,
+		       const struct repository *repo, const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", key, value);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_data_json_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    uint64_t us_elapsed_region, const char *category,
+			    const struct repository *repo, const char *key,
+			    const struct json_writer *value)
+{
+	const char *event_name = "data_json";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", key, value->json.buf);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute, const char *fmt,
+			    va_list ap)
+{
+	const char *event_name = "printf";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_perf = {
+	&tr2dst_perf,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	fn_data_json_fl,
+	fn_printf_va_fl,
+};
diff --git a/trace2/tr2_tls.c b/trace2/tr2_tls.c
new file mode 100644
index 00000000000000..e76d8c5d92aec7
--- /dev/null
+++ b/trace2/tr2_tls.c
@@ -0,0 +1,174 @@
+#include "cache.h"
+#include "thread-utils.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * Initialize size of the thread stack for nested regions.
+ * This is used to store nested region start times.  Note that
+ * this stack is per-thread and not per-trace-key.
+ */
+#define TR2_REGION_NESTING_INITIAL_SIZE (100)
+
+static struct tr2tls_thread_ctx *tr2tls_thread_main;
+static uint64_t tr2tls_us_start_process;
+
+static pthread_mutex_t tr2tls_mutex;
+static pthread_key_t tr2tls_key;
+
+static int tr2_next_thread_id; /* modify under lock */
+
+void tr2tls_start_process_clock(void)
+{
+	if (tr2tls_us_start_process)
+		return;
+
+	/*
+	 * Keep the absolute start time of the process (i.e. the main
+	 * process) in a fixed variable since other threads need to
+	 * access it.  This allows them to do that without a lock on
+	 * main thread's array data (because of reallocs).
+	 */
+	tr2tls_us_start_process = getnanotime() / 1000;
+}
+
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
+					     uint64_t us_thread_start)
+{
+	struct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));
+
+	/*
+	 * Implicitly "tr2tls_push_self()" to capture the thread's start
+	 * time in array_us_start[0].  For the main thread this gives us the
+	 * application run time.
+	 */
+	ctx->alloc = TR2_REGION_NESTING_INITIAL_SIZE;
+	ctx->array_us_start = (uint64_t *)xcalloc(ctx->alloc, sizeof(uint64_t));
+	ctx->array_us_start[ctx->nr_open_regions++] = us_thread_start;
+
+	ctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
+
+	strbuf_init(&ctx->thread_name, 0);
+	if (ctx->thread_id)
+		strbuf_addf(&ctx->thread_name, "th%02d:", ctx->thread_id);
+	strbuf_addstr(&ctx->thread_name, thread_name);
+	if (ctx->thread_name.len > TR2_MAX_THREAD_NAME)
+		strbuf_setlen(&ctx->thread_name, TR2_MAX_THREAD_NAME);
+
+	pthread_setspecific(tr2tls_key, ctx);
+
+	return ctx;
+}
+
+struct tr2tls_thread_ctx *tr2tls_get_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = pthread_getspecific(tr2tls_key);
+
+	/*
+	 * If the thread-proc did not call trace2_thread_start(), we won't
+	 * have any TLS data associated with the current thread.  Fix it
+	 * here and silently continue.
+	 */
+	if (!ctx)
+		ctx = tr2tls_create_self("unknown", getnanotime() / 1000);
+
+	return ctx;
+}
+
+int tr2tls_is_main_thread(void)
+{
+	struct tr2tls_thread_ctx *ctx = pthread_getspecific(tr2tls_key);
+
+	return ctx == tr2tls_thread_main;
+}
+
+void tr2tls_unset_self(void)
+{
+	struct tr2tls_thread_ctx *ctx;
+
+	ctx = tr2tls_get_self();
+
+	pthread_setspecific(tr2tls_key, NULL);
+
+	free(ctx->array_us_start);
+	free(ctx);
+}
+
+void tr2tls_push_self(uint64_t us_now)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	ALLOC_GROW(ctx->array_us_start, ctx->nr_open_regions + 1, ctx->alloc);
+	ctx->array_us_start[ctx->nr_open_regions++] = us_now;
+}
+
+void tr2tls_pop_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	if (!ctx->nr_open_regions)
+		BUG("no open regions in thread '%s'", ctx->thread_name.buf);
+
+	ctx->nr_open_regions--;
+}
+
+void tr2tls_pop_unwind_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	while (ctx->nr_open_regions > 1)
+		tr2tls_pop_self();
+}
+
+uint64_t tr2tls_region_elasped_self(uint64_t us)
+{
+	struct tr2tls_thread_ctx *ctx;
+	uint64_t us_start;
+
+	ctx = tr2tls_get_self();
+	if (!ctx->nr_open_regions)
+		return 0;
+
+	us_start = ctx->array_us_start[ctx->nr_open_regions - 1];
+
+	return us - us_start;
+}
+
+uint64_t tr2tls_absolute_elapsed(uint64_t us)
+{
+	if (!tr2tls_thread_main)
+		return 0;
+
+	return us - tr2tls_us_start_process;
+}
+
+void tr2tls_init(void)
+{
+	tr2tls_start_process_clock();
+
+	pthread_key_create(&tr2tls_key, NULL);
+	init_recursive_mutex(&tr2tls_mutex);
+
+	tr2tls_thread_main =
+		tr2tls_create_self("main", tr2tls_us_start_process);
+}
+
+void tr2tls_release(void)
+{
+	tr2tls_unset_self();
+	tr2tls_thread_main = NULL;
+
+	pthread_mutex_destroy(&tr2tls_mutex);
+	pthread_key_delete(tr2tls_key);
+}
+
+int tr2tls_locked_increment(int *p)
+{
+	int current_value;
+
+	pthread_mutex_lock(&tr2tls_mutex);
+	current_value = *p;
+	*p = current_value + 1;
+	pthread_mutex_unlock(&tr2tls_mutex);
+
+	return current_value;
+}
diff --git a/trace2/tr2_tls.h b/trace2/tr2_tls.h
new file mode 100644
index 00000000000000..b1e327a928e2ba
--- /dev/null
+++ b/trace2/tr2_tls.h
@@ -0,0 +1,103 @@
+#ifndef TR2_TLS_H
+#define TR2_TLS_H
+
+#include "strbuf.h"
+
+/*
+ * Arbitry limit for thread names for column alignment.
+ */
+#define TR2_MAX_THREAD_NAME (24)
+
+struct tr2tls_thread_ctx {
+	struct strbuf thread_name;
+	uint64_t *array_us_start;
+	int alloc;
+	int nr_open_regions; /* plays role of "nr" in ALLOC_GROW */
+	int thread_id;
+};
+
+/*
+ * Create TLS data for the current thread.  This gives us a place to
+ * put per-thread data, such as thread start time, function nesting
+ * and a per-thread label for our messages.
+ *
+ * We assume the first thread is "main".  Other threads are given
+ * non-zero thread-ids to help distinguish messages from concurrent
+ * threads.
+ *
+ * Truncate the thread name if necessary to help with column alignment
+ * in printf-style messages.
+ *
+ * In this and all following functions the term "self" refers to the
+ * current thread.
+ */
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
+					     uint64_t us_thread_start);
+
+/*
+ * Get our TLS data.
+ */
+struct tr2tls_thread_ctx *tr2tls_get_self(void);
+
+/*
+ * return true if the current thread is the main thread.
+ */
+int tr2tls_is_main_thread(void);
+
+/*
+ * Free our TLS data.
+ */
+void tr2tls_unset_self(void);
+
+/*
+ * Begin a new nested region and remember the start time.
+ */
+void tr2tls_push_self(uint64_t us_now);
+
+/*
+ * End the innermost nested region.
+ */
+void tr2tls_pop_self(void);
+
+/*
+ * Pop any extra (above the first) open regions on the current
+ * thread and discard.  During a thread-exit, we should only
+ * have region[0] that was pushed in trace2_thread_start() if
+ * the thread exits normally.
+ */
+void tr2tls_pop_unwind_self(void);
+
+/*
+ * Compute the elapsed time since the innermost region in the
+ * current thread started and the given time (usually now).
+ */
+uint64_t tr2tls_region_elasped_self(uint64_t us);
+
+/*
+ * Compute the elapsed time since the main thread started
+ * and the given time (usually now).  This is assumed to
+ * be the absolute run time of the process.
+ */
+uint64_t tr2tls_absolute_elapsed(uint64_t us);
+
+/*
+ * Initialize the tr2 TLS system.
+ */
+void tr2tls_init(void);
+
+/*
+ * Free all tr2 TLS resources.
+ */
+void tr2tls_release(void);
+
+/*
+ * Protected increment of an integer.
+ */
+int tr2tls_locked_increment(int *p);
+
+/*
+ * Capture the process start time and do nothing else.
+ */
+void tr2tls_start_process_clock(void);
+
+#endif /* TR2_TLS_H */
diff --git a/transport-helper.c b/transport-helper.c
index 17b4fa3fafeb03..16fb4347bae025 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -129,6 +129,8 @@ static struct child_process *get_helper(struct transport *transport)
 		argv_array_pushf(&helper->env_array, "%s=%s",
 				 GIT_DIR_ENVIRONMENT, get_git_dir());
 
+	helper->trace2_child_class = helper->args.argv[0]; /* "remote-<name>" */
+
 	code = start_command(helper);
 	if (code < 0 && errno == ENOENT)
 		die(_("unable to find remote helper for '%s'"), data->name);
diff --git a/transport.c b/transport.c
index e078812897edde..d0608df5c90cab 100644
--- a/transport.c
+++ b/transport.c
@@ -1062,6 +1062,7 @@ static int run_pre_push_hook(struct transport *transport,
 
 	proc.argv = argv;
 	proc.in = -1;
+	proc.trace2_hook_name = "pre-push";
 
 	if (start_command(&proc)) {
 		finish_command(&proc);
diff --git a/unpack-trees.c b/unpack-trees.c
index 3563daae1aa6bc..b3eb19c8bf57d6 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -17,6 +17,8 @@
 #include "fsmonitor.h"
 #include "object-store.h"
 #include "fetch-object.h"
+#include "gvfs.h"
+#include "virtualfilesystem.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -521,7 +523,9 @@ static int apply_sparse_checkout(struct index_state *istate,
 		 */
 		if (!(ce->ce_flags & CE_UPDATE) && verify_uptodate_sparse(ce, o))
 			return -1;
-		ce->ce_flags |= CE_WT_REMOVE;
+		if (!gvfs_config_is_set(GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT))
+			ce->ce_flags |= CE_WT_REMOVE;
+
 		ce->ce_flags &= ~CE_UPDATE;
 	}
 	if (was_skip_worktree && !ce_skip_worktree(ce)) {
@@ -1362,6 +1366,14 @@ static int clear_ce_flags_1(struct index_state *istate,
 			continue;
 		}
 
+		/* if it's not in the virtual file system, exit early */
+		if (core_virtualfilesystem) {
+			if (is_included_in_virtualfilesystem(ce->name, ce->ce_namelen) > 0)
+				ce->ce_flags &= ~clear_mask;
+			cache++;
+			continue;
+		}
+
 		if (prefix->len && strncmp(ce->name, prefix->buf, prefix->len))
 			break;
 
@@ -1414,15 +1426,23 @@ static int clear_ce_flags(struct index_state *istate,
 			  struct exclude_list *el)
 {
 	static struct strbuf prefix = STRBUF_INIT;
+	char label[100];
+	int rval;
 
 	strbuf_reset(&prefix);
 
-	return clear_ce_flags_1(istate,
+	xsnprintf(label, sizeof(label), "clear_ce_flags(0x%08lx,0x%08lx)",
+		  (unsigned long)select_mask, (unsigned long)clear_mask);
+	trace2_region_enter("exp", label, the_repository);
+	rval = clear_ce_flags_1(istate,
 				istate->cache,
 				istate->cache_nr,
 				&prefix,
 				select_mask, clear_mask,
 				el, 0);
+	trace2_region_leave("exp", label, the_repository);
+
+	return rval;
 }
 
 /*
@@ -1480,12 +1500,16 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	if (!core_apply_sparse_checkout || !o->update)
 		o->skip_sparse_checkout = 1;
 	if (!o->skip_sparse_checkout) {
-		char *sparse = git_pathdup("info/sparse-checkout");
-		if (add_excludes_from_file_to_list(sparse, "", 0, &el, NULL) < 0)
-			o->skip_sparse_checkout = 1;
-		else
+		if (core_virtualfilesystem) {
 			o->el = &el;
-		free(sparse);
+		} else {
+			char *sparse = git_pathdup("info/sparse-checkout");
+			if (add_excludes_from_file_to_list(sparse, "", 0, &el, NULL) < 0)
+				o->skip_sparse_checkout = 1;
+			else
+				o->el = &el;
+			free(sparse);
+		}
 	}
 
 	memset(&o->result, 0, sizeof(o->result));
@@ -1549,7 +1573,9 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		}
 
 		trace_performance_enter();
+		trace2_region_enter("exp", "traverse_trees", the_repository);
 		ret = traverse_trees(o->src_index, len, t, &info);
+		trace2_region_leave("exp", "traverse_trees", the_repository);
 		trace_performance_leave("traverse_trees");
 		if (ret < 0)
 			goto return_failed;
@@ -1577,7 +1603,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 
 		/*
 		 * Sparse checkout loop #2: set NEW_SKIP_WORKTREE on entries not in loop #1
-		 * If the will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
+		 * If they will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
 		 * so apply_sparse_checkout() won't attempt to remove it from worktree
 		 */
 		mark_new_skip_worktree(o->el, &o->result, CE_ADDED, CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
@@ -1637,6 +1663,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
+
+		o->result.updated_workdir = 1;
 		discard_index(o->dst_index);
 		*o->dst_index = o->result;
 	} else {
@@ -2088,6 +2116,27 @@ static int deleted_entry(const struct cache_entry *ce,
 	}
 	if (!(old->ce_flags & CE_CONFLICTED) && verify_uptodate(old, o))
 		return -1;
+
+	/*
+	 * When marking entries to remove from the index and the working
+	 * directory this option will take into account what the
+	 * skip-worktree bit was set to so that if the entry has the
+	 * skip-worktree bit set it will not be removed from the working
+	 * directory.  This will allow virtualized working directories to
+	 * detect the change to HEAD and use the new commit tree to show
+	 * the files that are in the working directory.
+	 *
+	 * old is the cache_entry that will have the skip-worktree bit set
+	 * which will need to be preserved when the CE_REMOVE entry is added
+	 */
+	if (gvfs_config_is_set(GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT) &&
+		old &&
+		old->ce_flags & CE_SKIP_WORKTREE) {
+		add_entry(o, old, CE_REMOVE, 0);
+		invalidate_ce_path(old, o);
+		return 1;
+	}
+
 	add_entry(o, ce, CE_REMOVE, 0);
 	invalidate_ce_path(ce, o);
 	return 1;
diff --git a/usage.c b/usage.c
index cc803336bd5e67..2fdb20086bd695 100644
--- a/usage.c
+++ b/usage.c
@@ -22,17 +22,48 @@ void vreportf(const char *prefix, const char *err, va_list params)
 static NORETURN void usage_builtin(const char *err, va_list params)
 {
 	vreportf("usage: ", err, params);
+
+	/*
+	 * When we detect a usage error *before* the command dispatch in
+	 * cmd_main(), we don't know what verb to report.  Force it to this
+	 * to facilitate post-processing.
+	 */
+	trace2_cmd_name("_usage_");
+
+	/*
+	 * Currently, the (err, params) are usually just the static usage
+	 * string which isn't very useful here.  Usually, the call site
+	 * manually calls fprintf(stderr,...) with the actual detailed
+	 * syntax error before calling usage().
+	 *
+	 * TODO It would be nice to update the call sites to pass both
+	 * the static usage string and the detailed error message.
+	 */
+
 	exit(129);
 }
 
 static NORETURN void die_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("fatal: ", err, params);
+
 	exit(128);
 }
 
 static void error_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("error: ", err, params);
 }
 
diff --git a/virtualfilesystem.c b/virtualfilesystem.c
new file mode 100644
index 00000000000000..7b935b0fe3fa7b
--- /dev/null
+++ b/virtualfilesystem.c
@@ -0,0 +1,341 @@
+#include "cache.h"
+#include "config.h"
+#include "dir.h"
+#include "hashmap.h"
+#include "run-command.h"
+#include "virtualfilesystem.h"
+
+#define HOOK_INTERFACE_VERSION	(1)
+
+static struct strbuf virtual_filesystem_data = STRBUF_INIT;
+static struct hashmap virtual_filesystem_hashmap;
+static struct hashmap parent_directory_hashmap;
+
+struct virtualfilesystem {
+	struct hashmap_entry ent; /* must be the first member! */
+	const char *pattern;
+	int patternlen;
+};
+
+static unsigned int(*vfshash)(const void *buf, size_t len);
+static int(*vfscmp)(const char *a, const char *b, size_t len);
+
+static int vfs_hashmap_cmp(const void *unused_cmp_data,
+	const void *a, const void *b, const void *key)
+{
+	const struct virtualfilesystem *vfs1 = a;
+	const struct virtualfilesystem *vfs2 = b;
+
+	return vfscmp(vfs1->pattern, vfs2->pattern, vfs1->patternlen);
+}
+
+static void get_virtual_filesystem_data(struct strbuf *vfs_data)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	int err;
+
+	strbuf_init(vfs_data, 0);
+
+	argv_array_push(&cp.args, core_virtualfilesystem);
+	argv_array_pushf(&cp.args, "%d", HOOK_INTERFACE_VERSION);
+	cp.use_shell = 1;
+	cp.dir = get_git_work_tree();
+
+	err = capture_command(&cp, vfs_data, 1024);
+	if (err)
+		die("unable to load virtual file system");
+}
+
+static int check_includes_hashmap(struct hashmap *map, const char *pattern, int patternlen)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct virtualfilesystem vfs;
+	char *slash;
+
+	/* Check straight mapping */
+	strbuf_reset(&sb);
+	strbuf_add(&sb, pattern, patternlen);
+	vfs.pattern = sb.buf;
+	vfs.patternlen = sb.len;
+	hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+	if (hashmap_get(map, &vfs, NULL)) {
+		strbuf_release(&sb);
+		return 1;
+	}
+
+	/*
+	 * Check to see if it matches a directory or any path
+	 * underneath it.  In other words, 'a/b/foo.txt' will match
+	 * '/', 'a/', and 'a/b/'.
+	 */
+	slash = strchr(sb.buf, '/');
+	while (slash) {
+		vfs.pattern = sb.buf;
+		vfs.patternlen = slash - sb.buf + 1;
+		hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+		if (hashmap_get(map, &vfs, NULL)) {
+			strbuf_release(&sb);
+			return 1;
+		}
+		slash = strchr(slash + 1, '/');
+	}
+
+	strbuf_release(&sb);
+	return 0;
+}
+
+static void includes_hashmap_add(struct hashmap *map, const char *pattern, const int patternlen)
+{
+	struct virtualfilesystem *vfs;
+
+	vfs = xmalloc(sizeof(struct virtualfilesystem));
+	vfs->pattern = pattern;
+	vfs->patternlen = patternlen;
+	hashmap_entry_init(vfs, vfshash(vfs->pattern, vfs->patternlen));
+	hashmap_add(map, vfs);
+}
+
+static void initialize_includes_hashmap(struct hashmap *map, struct strbuf *vfs_data)
+{
+	char *buf, *entry;
+	size_t len;
+	int i;
+
+	/*
+	 * Build a hashmap of the virtual file system data we can use to look
+	 * for cache entry matches quickly
+	 */
+	vfshash = ignore_case ? memihash : memhash;
+	vfscmp = ignore_case ? strncasecmp : strncmp;
+	hashmap_init(map, vfs_hashmap_cmp, NULL, 0);
+
+	entry = buf = vfs_data->buf;
+	len = vfs_data->len;
+	for (i = 0; i < len; i++) {
+		if (buf[i] == '\0') {
+			includes_hashmap_add(map, entry, buf + i - entry);
+			entry = buf + i + 1;
+		}
+	}
+}
+
+/*
+ * Return 1 if the requested item is found in the virtual file system,
+ * 0 for not found and -1 for undecided.
+ */
+int is_included_in_virtualfilesystem(const char *pathname, int pathlen)
+{
+	if (!core_virtualfilesystem)
+		return -1;
+
+	if (!virtual_filesystem_hashmap.tablesize && virtual_filesystem_data.len)
+		initialize_includes_hashmap(&virtual_filesystem_hashmap, &virtual_filesystem_data);
+	if (!virtual_filesystem_hashmap.tablesize)
+		return -1;
+	
+	return check_includes_hashmap(&virtual_filesystem_hashmap, pathname, pathlen);
+}
+
+static void parent_directory_hashmap_add(struct hashmap *map, const char *pattern, const int patternlen)
+{
+	char *slash;
+	struct virtualfilesystem *vfs;
+
+	/*
+	 * Add any directories leading up to the file as the excludes logic
+	 * needs to match directories leading up to the files as well. Detect
+	 * and prevent unnecessary duplicate entries which will be common.
+	 */
+	if (patternlen > 1) {
+		slash = strchr(pattern + 1, '/');
+		while (slash) {
+			vfs = xmalloc(sizeof(struct virtualfilesystem));
+			vfs->pattern = pattern;
+			vfs->patternlen = slash - pattern + 1;
+			hashmap_entry_init(vfs, vfshash(vfs->pattern, vfs->patternlen));
+			if (hashmap_get(map, vfs, NULL))
+				free(vfs);
+			else
+				hashmap_add(map, vfs);
+			slash = strchr(slash + 1, '/');
+		}
+	}
+}
+
+static void initialize_parent_directory_hashmap(struct hashmap *map, struct strbuf *vfs_data)
+{
+	char *buf, *entry;
+	size_t len;
+	int i;
+
+	/*
+	 * Build a hashmap of the parent directories contained in the virtual
+	 * file system data we can use to look for matches quickly
+	 */
+	vfshash = ignore_case ? memihash : memhash;
+	vfscmp = ignore_case ? strncasecmp : strncmp;
+	hashmap_init(map, vfs_hashmap_cmp, NULL, 0);
+
+	entry = buf = vfs_data->buf;
+	len = vfs_data->len;
+	for (i = 0; i < len; i++) {
+		if (buf[i] == '\0') {
+			parent_directory_hashmap_add(map, entry, buf + i - entry);
+			entry = buf + i + 1;
+		}
+	}
+}
+
+static int check_directory_hashmap(struct hashmap *map, const char *pathname, int pathlen)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct virtualfilesystem vfs;
+
+	/* Check for directory */
+	strbuf_reset(&sb);
+	strbuf_add(&sb, pathname, pathlen);
+	strbuf_addch(&sb, '/');
+	vfs.pattern = sb.buf;
+	vfs.patternlen = sb.len;
+	hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+	if (hashmap_get(map, &vfs, NULL)) {
+		strbuf_release(&sb);
+		return 0;
+	}
+
+	strbuf_release(&sb);
+	return 1;
+}
+
+/*
+ * Return 1 for exclude, 0 for include and -1 for undecided.
+ */
+int is_excluded_from_virtualfilesystem(const char *pathname, int pathlen, int dtype)
+{
+	if (!core_virtualfilesystem)
+		return -1;
+
+	if (dtype != DT_REG && dtype != DT_DIR && dtype != DT_LNK)
+		die(_("is_excluded_from_virtualfilesystem passed unhandled dtype"));
+
+	if (dtype == DT_REG || dtype == DT_LNK) {
+		int ret = is_included_in_virtualfilesystem(pathname, pathlen);
+		if (ret > 0)
+			return 0;
+		if (ret == 0)
+			return 1;
+		return ret;
+	}
+
+	if (dtype == DT_DIR) {
+		int ret = is_included_in_virtualfilesystem(pathname, pathlen);
+		if (ret > 0)
+			return 0;
+
+		if (!parent_directory_hashmap.tablesize && virtual_filesystem_data.len)
+			initialize_parent_directory_hashmap(&parent_directory_hashmap, &virtual_filesystem_data);
+		if (!parent_directory_hashmap.tablesize)
+			return -1;
+
+		return check_directory_hashmap(&parent_directory_hashmap, pathname, pathlen);
+	}
+
+	return -1;
+}
+
+/*
+ * Update the CE_SKIP_WORKTREE bits based on the virtual file system.
+ */
+void apply_virtualfilesystem(struct index_state *istate)
+{
+	char *buf, *entry;
+	int i;
+	int nr_unknown = 0;
+	int nr_vfs_dirs = 0;
+	int nr_vfs_rows = 0;
+	int nr_bulk_skip = 0;
+	int nr_explicit_skip = 0;
+
+	if (!git_config_get_virtualfilesystem())
+		return;
+
+	if (!virtual_filesystem_data.len)
+		get_virtual_filesystem_data(&virtual_filesystem_data);
+
+	/* set CE_SKIP_WORKTREE bit on all entries */
+	for (i = 0; i < istate->cache_nr; i++)
+		istate->cache[i]->ce_flags |= CE_SKIP_WORKTREE;
+
+	/* clear CE_SKIP_WORKTREE bit for everything in the virtual file system */
+	entry = buf = virtual_filesystem_data.buf;
+	for (i = 0; i < virtual_filesystem_data.len; i++) {
+		if (buf[i] == '\0') {
+			int pos, len;
+
+			nr_vfs_rows++;
+
+			len = buf + i - entry;
+
+			/* look for a directory wild card (ie "dir1/") */
+			if (buf[i - 1] == '/') {
+				nr_vfs_dirs++;
+				if (ignore_case)
+					adjust_dirname_case(istate, entry);
+				pos = index_name_pos(istate, entry, len);
+				if (pos < 0) {
+					pos = -pos - 1;
+					while (pos < istate->cache_nr && !fspathncmp(istate->cache[pos]->name, entry, len)) {
+						if (istate->cache[pos]->ce_flags & CE_SKIP_WORKTREE)
+							nr_bulk_skip++;
+						istate->cache[pos]->ce_flags &= ~CE_SKIP_WORKTREE;
+						pos++;
+					}
+				}
+			} else {
+				if (ignore_case) {
+					struct cache_entry *ce = index_file_exists(istate, entry, len, ignore_case);
+					if (ce) {
+						if (ce->ce_flags & CE_SKIP_WORKTREE)
+							nr_explicit_skip++;
+						ce->ce_flags &= ~CE_SKIP_WORKTREE;
+					}
+					else {
+						nr_unknown++;
+					}
+				} else {
+					int pos = index_name_pos(istate, entry, len);
+					if (pos >= 0) {
+						if (istate->cache[pos]->ce_flags & CE_SKIP_WORKTREE)
+							nr_explicit_skip++;
+						istate->cache[pos]->ce_flags &= ~CE_SKIP_WORKTREE;
+					}
+					else {
+						nr_unknown++;
+					}
+				}
+			}
+
+			entry += len + 1;
+		}
+	}
+
+	if (nr_vfs_rows > 0) {
+		trace2_data_intmax("vfs", the_repository, "apply/tracked", nr_bulk_skip + nr_explicit_skip);
+
+		trace2_data_intmax("vfs", the_repository, "apply/vfs_rows", nr_vfs_rows);
+		trace2_data_intmax("vfs", the_repository, "apply/vfs_dirs", nr_vfs_dirs);
+
+		trace2_data_intmax("vfs", the_repository, "apply/nr_unknown", nr_unknown);
+		trace2_data_intmax("vfs", the_repository, "apply/nr_bulk_skip", nr_bulk_skip);
+		trace2_data_intmax("vfs", the_repository, "apply/nr_explicit_skip", nr_explicit_skip);
+	}
+}
+
+/*
+ * Free the virtual file system data structures.
+ */
+void free_virtualfilesystem(void) {
+	hashmap_free(&virtual_filesystem_hashmap, 1);
+	hashmap_free(&parent_directory_hashmap, 1);
+	strbuf_release(&virtual_filesystem_data);
+}
diff --git a/virtualfilesystem.h b/virtualfilesystem.h
new file mode 100644
index 00000000000000..5e8c5b096df09a
--- /dev/null
+++ b/virtualfilesystem.h
@@ -0,0 +1,25 @@
+#ifndef VIRTUALFILESYSTEM_H
+#define VIRTUALFILESYSTEM_H
+
+/*
+ * Update the CE_SKIP_WORKTREE bits based on the virtual file system.
+ */
+void apply_virtualfilesystem(struct index_state *istate);
+
+/*
+ * Return 1 if the requested item is found in the virtual file system,
+ * 0 for not found and -1 for undecided.
+ */
+int is_included_in_virtualfilesystem(const char *pathname, int pathlen);
+
+/*
+ * Return 1 for exclude, 0 for include and -1 for undecided.
+ */
+int is_excluded_from_virtualfilesystem(const char *pathname, int pathlen, int dtype);
+
+/*
+ * Free the virtual file system data structures.
+ */
+void free_virtualfilesystem(void);
+
+#endif
diff --git a/walker.c b/walker.c
index d74ae59c77fb36..bf911b8456301c 100644
--- a/walker.c
+++ b/walker.c
@@ -82,7 +82,8 @@ static int process_commit(struct walker *walker, struct commit *commit)
 		return -1;
 
 	while (complete && complete->item->date >= commit->date) {
-		pop_most_recent_commit(&complete, COMPLETE);
+		pop_most_recent_commit(&complete, COMPLETE,
+				       GENERATION_NUMBER_ZERO);
 	}
 
 	if (commit->object.flags & COMPLETE)
diff --git a/wt-status-deserialize.c b/wt-status-deserialize.c
new file mode 100644
index 00000000000000..e1f7298bc758c5
--- /dev/null
+++ b/wt-status-deserialize.c
@@ -0,0 +1,863 @@
+#include "cache.h"
+#include "wt-status.h"
+#include "pkt-line.h"
+#include "trace.h"
+
+static void set_deserialize_reject_reason(const char *reason)
+{
+	trace2_data_string("status", the_repository, "deserialize/reject",
+			   reason);
+}
+
+int wt_status_deserialize_access(const char *path, int mode)
+{
+	int a = access(path, mode);
+
+	if (a != 0)
+		set_deserialize_reject_reason("status-cache/access");
+
+	return a;
+}
+
+static struct trace_key trace_deserialize = TRACE_KEY_INIT(DESERIALIZE);
+
+enum deserialize_parse_strategy {
+	DESERIALIZE_STRATEGY_AS_IS,
+	DESERIALIZE_STRATEGY_SKIP,
+	DESERIALIZE_STRATEGY_NORMAL,
+	DESERIALIZE_STRATEGY_ALL
+};
+
+static int check_path_contains(const char *out, int out_len, const char *in, int in_len)
+{
+	return (out_len > 0 &&
+		out_len < in_len &&
+		(out[out_len - 1] == '/') &&
+		!memcmp(out, in, out_len));
+}
+
+static const char *my_packet_read_line(int fd, int *line_len)
+{
+	static char buf[LARGE_PACKET_MAX];
+
+	*line_len = packet_read(fd, NULL, NULL, buf, sizeof(buf),
+				PACKET_READ_CHOMP_NEWLINE |
+				PACKET_READ_GENTLE_ON_EOF);
+	return (*line_len > 0) ? buf : NULL;
+}
+
+/*
+ * mtime_reported contains the mtime of the index when the
+ * serialization snapshot was computed.
+ *
+ * mtime_observed_on_disk contains the mtime of the index now.
+ *
+ * If these 2 times are different, then the .git/index has
+ * changed since the serialization cache was created and we
+ * must reject the cache because anything could have changed.
+ *
+ * If they are the same, we continue trying to use the cache.
+ */
+static int my_validate_index(const struct cache_time *mtime_reported)
+{
+	const char *path = get_index_file();
+	struct stat st;
+	struct cache_time mtime_observed_on_disk;
+
+	if (lstat(path, &st)) {
+		set_deserialize_reject_reason("index/not-found");
+		trace_printf_key(&trace_deserialize, "could not stat index");
+		return DESERIALIZE_ERR;
+	}
+	mtime_observed_on_disk.sec = st.st_mtime;
+	mtime_observed_on_disk.nsec = ST_MTIME_NSEC(st);
+	if ((mtime_observed_on_disk.sec != mtime_reported->sec) ||
+	    (mtime_observed_on_disk.nsec != mtime_reported->nsec)) {
+		set_deserialize_reject_reason("index/mtime-changed");
+		trace_printf_key(&trace_deserialize,
+				 "index mtime changed [des %d %d][obs %d %d]",
+			     mtime_reported->sec, mtime_reported->nsec,
+			     mtime_observed_on_disk.sec, mtime_observed_on_disk.nsec);
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+/*
+ * Use the given key and exclude pathname to compute a serialization header
+ * reflecting the current contents on disk.  See if that matches the value
+ * computed for this key when the cache was written.  Reject the cache if
+ * anything has changed.
+ */
+static int my_validate_excludes(const char *path, const char *key, const char *line)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int r;
+
+	wt_serialize_compute_exclude_header(&sb, key, path);
+
+	r = (strcmp(line, sb.buf) ? DESERIALIZE_ERR : DESERIALIZE_OK);
+
+	if (r == DESERIALIZE_ERR) {
+		set_deserialize_reject_reason("excludes/changed");
+		trace_printf_key(&trace_deserialize,
+				 "%s changed [cached '%s'][observed '%s']",
+				 key, line, sb.buf);
+	}
+
+	strbuf_release(&sb);
+	return r;
+}
+
+static int my_parse_core_excludes(const char *line)
+{
+	/*
+	 * In dir.c:setup_standard_excludes() they use either the value of
+	 * the "core.excludefile" variable (stored in the global "excludes_file"
+	 * variable) -or- the default value "$XDG_HOME/git/ignore".  This is done
+	 * during wt_status_collect_untracked() which we are hoping to not call.
+	 *
+	 * Fake the setup here.
+	 */
+
+	if (excludes_file) {
+		return my_validate_excludes(excludes_file, "core_excludes", line);
+	} else {
+		char *path = xdg_config_home("ignore");
+		int r = my_validate_excludes(path, "core_excludes", line);
+		free(path);
+		return r;
+	}
+}
+
+static int my_parse_repo_excludes(const char *line)
+{
+	char *path = git_pathdup("info/exclude");
+	int r = my_validate_excludes(path, "repo_excludes", line);
+	free(path);
+
+	return r;
+}
+
+static int wt_deserialize_v1_header(struct wt_status *s, int fd)
+{
+	struct cache_time index_mtime;
+	int line_len, nr_fields;
+	const char *line;
+	const char *arg;
+	int have_required_index_mtime = 0;
+	int have_required_core_excludes = 0;
+	int have_required_repo_excludes = 0;
+
+	/*
+	 * parse header lines up to the first flush packet.
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+
+		if (skip_prefix(line, "index_mtime ", &arg)) {
+			nr_fields = sscanf(arg, "%d %d",
+					   &index_mtime.sec,
+					   &index_mtime.nsec);
+			if (nr_fields != 2) {
+				set_deserialize_reject_reason("v1-header/invalid-index-mtime");
+				trace_printf_key(&trace_deserialize, "invalid index_mtime (%d) '%s'",
+					     nr_fields, line);
+				return DESERIALIZE_ERR;
+			}
+			have_required_index_mtime = 1;
+			continue;
+		}
+
+		if (skip_prefix(line, "core_excludes ", &arg)) {
+			if (my_parse_core_excludes(line) != DESERIALIZE_OK)
+				return DESERIALIZE_ERR;
+			have_required_core_excludes = 1;
+			continue;
+		}
+		if (skip_prefix(line, "repo_excludes ", &arg)) {
+			if (my_parse_repo_excludes(line) != DESERIALIZE_OK)
+				return DESERIALIZE_ERR;
+			have_required_repo_excludes = 1;
+			continue;
+		}
+
+		if (skip_prefix(line, "is_initial ", &arg)) {
+			s->is_initial = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "branch ", &arg)) {
+			s->branch = xstrdup(arg);
+			continue;
+		}
+		if (skip_prefix(line, "reference ", &arg)) {
+			s->reference = xstrdup(arg);
+			continue;
+		}
+		/* pathspec */
+		/* verbose */
+		/* amend */
+		if (skip_prefix(line, "whence ", &arg)) {
+			s->whence = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* nowarn */
+		/* use_color */
+		/* no_gettext */
+		/* display_comment_prefix */
+		/* relative_paths */
+		/* submodule_summary */
+		if (skip_prefix(line, "show_ignored_mode ", &arg)) {
+			s->show_ignored_mode = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "show_untracked_files ", &arg)) {
+			s->show_untracked_files = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "ignore_submodule_arg ", &arg)) {
+			s->ignore_submodule_arg = xstrdup(arg);
+			continue;
+		}
+		/* color_palette */
+		/* colopts */
+		/* null_termination */
+		/* commit_template */
+		/* show_branch */
+		/* show_stash */
+		if (skip_prefix(line, "hints ", &arg)) {
+			s->hints = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "detect_rename ", &arg)) {
+			s->detect_rename = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "rename_score ", &arg)) {
+			s->rename_score = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "rename_limit ", &arg)) {
+			s->rename_limit = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* status_format */
+		if (skip_prefix(line, "sha1_commit ", &arg)) {
+			if (get_sha1_hex(arg, s->sha1_commit)) {
+				set_deserialize_reject_reason("v1-header/invalid-commit-sha");
+				trace_printf_key(&trace_deserialize, "invalid sha1_commit");
+				return DESERIALIZE_ERR;
+			}
+			continue;
+		}
+		if (skip_prefix(line, "committable ", &arg)) {
+			s->committable = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "workdir_dirty ", &arg)) {
+			s->workdir_dirty = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* prefix */
+
+		set_deserialize_reject_reason("v1-header/unexpected-line");
+		trace_printf_key(&trace_deserialize, "unexpected line '%s'", line);
+		return DESERIALIZE_ERR;
+	}
+
+	if (!have_required_index_mtime) {
+		set_deserialize_reject_reason("v1-header/missing-index-mtime");
+		trace_printf_key(&trace_deserialize, "missing '%s'", "index_mtime");
+		return DESERIALIZE_ERR;
+	}
+	if (!have_required_core_excludes) {
+		set_deserialize_reject_reason("v1-header/missing-core-excludes");
+		trace_printf_key(&trace_deserialize, "missing '%s'", "core_excludes");
+		return DESERIALIZE_ERR;
+	}
+	if (!have_required_repo_excludes) {
+		set_deserialize_reject_reason("v1-header/missing-repo-excludes");
+		trace_printf_key(&trace_deserialize, "missing '%s'", "repo_excludes");
+		return DESERIALIZE_ERR;
+	}
+
+	return my_validate_index(&index_mtime);
+}
+
+/*
+ * Build a string-list of (count) <changed-item> lines from the input.
+ */
+static int wt_deserialize_v1_changed_items(const struct wt_status *cmd_s,
+					   struct wt_status *s, int fd, int count)
+{
+	struct wt_status_serialize_data *sd;
+	char *p;
+	int line_len;
+	const char *line;
+	struct string_list_item *item;
+
+	string_list_init(&s->change, 1);
+
+	/*
+	 * <wt_status_change_data_fields>+
+	 * <flush>
+	 *
+	 * <fixed_part><path> NUL [<head_path>] NUL
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		struct wt_status_change_data *d = xcalloc(1, sizeof(*d));
+		sd = (struct wt_status_serialize_data *)line;
+
+		d->worktree_status = ntohl(sd->fixed.worktree_status);
+		d->index_status = ntohl(sd->fixed.index_status);
+		d->stagemask = ntohl(sd->fixed.stagemask);
+		d->rename_status = ntohl(sd->fixed.rename_status);
+		d->rename_score = ntohl(sd->fixed.rename_score);
+		d->mode_head = ntohl(sd->fixed.mode_head);
+		d->mode_index = ntohl(sd->fixed.mode_index);
+		d->mode_worktree = ntohl(sd->fixed.mode_worktree);
+		d->dirty_submodule = ntohl(sd->fixed.dirty_submodule);
+		d->new_submodule_commits = ntohl(sd->fixed.new_submodule_commits);
+		oidcpy(&d->oid_head, &sd->fixed.oid_head);
+		oidcpy(&d->oid_index, &sd->fixed.oid_index);
+
+		p = sd->variant;
+		item = string_list_append(&s->change, p);
+		p += strlen(p) + 1;
+		if (*p)
+			d->rename_source = xstrdup(p);
+		item->util = d;
+		
+		trace_printf_key(
+			&trace_deserialize,
+			"change: %d %d %d %d %d %o %o %o %d %d %s %s '%s' '%s'",
+			d->worktree_status,
+			d->index_status,
+			d->stagemask,
+			d->rename_status,
+			d->rename_score,
+			d->mode_head,
+			d->mode_index,
+			d->mode_worktree,
+			d->dirty_submodule,
+			d->new_submodule_commits,
+			oid_to_hex(&d->oid_head),
+			oid_to_hex(&d->oid_index),
+			item->string,
+			(d->rename_source ? d->rename_source : ""));
+
+		if (d->stagemask &&
+		    cmd_s->status_format == STATUS_FORMAT_PORCELAIN_V2) {
+			/*
+			 * We have an unresolved conflict and the user wants
+			 * to see porcelain V2 output.  The cached status data
+			 * does not contain enough information for V2 (because
+			 * the main status computation does not capture it).
+			 * We only get a single change record for the file with
+			 * a single SHA -- we don't get the stage [123] mode
+			 * and SHA data.  The V2 detail-line print code looks
+			 * up this information directly from the index.  The
+			 * whole point of this serialization cache is to avoid
+			 * reading the index, so the V2 print code gets zeros.
+			 * So we reject the status cache and let the fallback
+			 * code run.
+			 */
+			set_deserialize_reject_reason("v1-data/unmerged");
+			trace_printf_key(
+				&trace_deserialize,
+				"reject: V2 format and umerged file: %s",
+				item->string);
+			return DESERIALIZE_ERR;
+		}
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1_untracked_items(struct wt_status *s,
+					     int fd,
+					     int count,
+					     enum deserialize_parse_strategy strategy)
+{
+	int line_len;
+	const char *line;
+	char *out = NULL;
+	int out_len = 0;
+
+	string_list_init(&s->untracked, 1);
+
+	/*
+	 * <pathname>+
+	 * <flush>
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (strategy == DESERIALIZE_STRATEGY_AS_IS)
+			string_list_append(&s->untracked, line);
+		if (strategy == DESERIALIZE_STRATEGY_SKIP)
+			continue;
+		if (strategy == DESERIALIZE_STRATEGY_NORMAL) {
+
+			/* Only add "normal" entries to list */
+			if (out &&
+				check_path_contains(out, out_len, line, line_len)) {
+				continue;
+			}
+			else {
+				out = string_list_append(&s->untracked, line)->string;
+				out_len = line_len;
+			}
+		}
+		if (strategy == DESERIALIZE_STRATEGY_ALL) {
+			/* Only add "all" entries to list */
+			if (line[line_len - 1] != '/')
+				string_list_append(&s->untracked, line);
+		}
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1_ignored_items(struct wt_status *s,
+					   int fd,
+					   int count,
+					   enum deserialize_parse_strategy strategy)
+{
+	int line_len;
+	const char *line;
+
+	string_list_init(&s->ignored, 1);
+
+	/*
+	 * <pathname>+
+	 * <flush>
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (strategy == DESERIALIZE_STRATEGY_AS_IS)
+			string_list_append(&s->ignored, line);
+		else
+			continue;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int validate_untracked_files_arg(enum untracked_status_type cmd,
+					enum untracked_status_type des,
+					enum deserialize_parse_strategy *strategy)
+{
+	*strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (cmd == des) {
+		*strategy = DESERIALIZE_STRATEGY_AS_IS;
+	} else if (cmd == SHOW_NO_UNTRACKED_FILES) {
+		*strategy = DESERIALIZE_STRATEGY_SKIP;
+	} else if (des == SHOW_COMPLETE_UNTRACKED_FILES) {
+		if (cmd == SHOW_ALL_UNTRACKED_FILES)
+			*strategy = DESERIALIZE_STRATEGY_ALL;
+		else if (cmd == SHOW_NORMAL_UNTRACKED_FILES)
+			*strategy = DESERIALIZE_STRATEGY_NORMAL;
+	} else {
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int validate_ignored_files_arg(enum show_ignored_type cmd,
+				      enum show_ignored_type des,
+				      enum deserialize_parse_strategy *strategy)
+{
+	*strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (cmd == SHOW_NO_IGNORED) {
+		*strategy = DESERIALIZE_STRATEGY_SKIP;
+	}
+	else if (cmd != des) {
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1(const struct wt_status *cmd_s, struct wt_status *s, int fd)
+{
+	int line_len;
+	const char *line;
+	const char *arg;
+	int nr_changed = 0;
+	int nr_untracked = 0;
+	int nr_ignored = 0;
+
+	enum deserialize_parse_strategy ignored_strategy = DESERIALIZE_STRATEGY_AS_IS, untracked_strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (wt_deserialize_v1_header(s, fd) == DESERIALIZE_ERR)
+		return DESERIALIZE_ERR;
+
+	/*
+	 * We now have the header parsed. Look at the command args (as passed in), and see how to parse
+	 * the serialized data
+	*/
+	if (validate_untracked_files_arg(cmd_s->show_untracked_files, s->show_untracked_files, &untracked_strategy)) {
+		set_deserialize_reject_reason("args/untracked-files");
+		trace_printf_key(&trace_deserialize, "reject: show_untracked_file: command: %d, serialized : %d",
+				cmd_s->show_untracked_files,
+				s->show_untracked_files);
+		return DESERIALIZE_ERR;
+	}
+
+	if (validate_ignored_files_arg(cmd_s->show_ignored_mode, s->show_ignored_mode, &ignored_strategy)) {
+		set_deserialize_reject_reason("args/ignored-mode");
+		trace_printf_key(&trace_deserialize, "reject: show_ignored_mode: command: %d, serialized: %d",
+				cmd_s->show_ignored_mode,
+				s->show_ignored_mode);
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * [<changed-header> [<changed-item>+] <flush>]
+	 * [<untracked-header> [<untracked-item>+] <flush>]
+	 * [<ignored-header> [<ignored-item>+] <flush>]
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (skip_prefix(line, "changed ", &arg)) {
+			nr_changed = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_changed_items(cmd_s, s, fd, nr_changed)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		if (skip_prefix(line, "untracked ", &arg)) {
+			nr_untracked = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_untracked_items(s, fd, nr_untracked, untracked_strategy)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		if (skip_prefix(line, "ignored ", &arg)) {
+			nr_ignored = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_ignored_items(s, fd, nr_ignored, ignored_strategy)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		set_deserialize_reject_reason("v1-data/unexpected-line");
+		trace_printf_key(&trace_deserialize, "unexpected line '%s'", line);
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_parse(const struct wt_status *cmd_s, struct wt_status *s, int fd)
+{
+	int line_len;
+	const char *line;
+	const char *arg;
+
+	memset(s, 0, sizeof(*s));
+
+	if ((line = my_packet_read_line(fd, &line_len)) &&
+	    (skip_prefix(line, "version ", &arg))) {
+		int version = (int)strtol(arg, NULL, 10);
+		if (version == 1)
+			return wt_deserialize_v1(cmd_s, s, fd);
+	}
+	set_deserialize_reject_reason("status-cache/unsupported-version");
+	trace_printf_key(&trace_deserialize, "missing/unsupported version");
+	return DESERIALIZE_ERR;
+}
+
+static inline int my_strcmp_null(const char *a, const char *b)
+{
+	const char *alt_a = (a) ? a : "";
+	const char *alt_b = (b) ? b : "";
+
+	return strcmp(alt_a, alt_b);
+}
+
+static int wt_deserialize_fd(const struct wt_status *cmd_s, struct wt_status *des_s, int fd)
+{
+	memset(des_s, 0, sizeof(*des_s));
+
+	/*
+	 * Check the path spec on the current command
+	 */
+	if (cmd_s->pathspec.nr > 1) {
+		set_deserialize_reject_reason("args/multiple-pathspecs");
+		trace_printf_key(&trace_deserialize, "reject: multiple pathspecs");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * If we have a pathspec, but it maches the root (e.g. no filtering)
+	 * then this is OK.
+	 */
+	if (cmd_s->pathspec.nr == 1 &&
+		my_strcmp_null(cmd_s->pathspec.items[0].match, "")) {
+		set_deserialize_reject_reason("args/root-pathspec");
+		trace_printf_key(&trace_deserialize, "reject: pathspec");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * Deserialize cached status
+	 */
+	if (wt_deserialize_parse(cmd_s, des_s, fd) == DESERIALIZE_ERR)
+		return DESERIALIZE_ERR;
+
+	/*
+	 * Compare fields in cmd_s with those observed in des_s and
+	 * complain if they are incompatible (such as different "-u"
+	 * or "--ignored" settings).
+	 */
+	if (cmd_s->is_initial != des_s->is_initial) {
+		set_deserialize_reject_reason("args/is-initial-changed");
+		trace_printf_key(&trace_deserialize, "reject: is_initial");
+		return DESERIALIZE_ERR;
+	}
+	if (my_strcmp_null(cmd_s->branch, des_s->branch)) {
+		set_deserialize_reject_reason("args/branch-changed");
+		trace_printf_key(&trace_deserialize, "reject: branch");
+		return DESERIALIZE_ERR;
+	}
+	if (my_strcmp_null(cmd_s->reference, des_s->reference)) {
+		set_deserialize_reject_reason("args/reference-changed");
+		trace_printf_key(&trace_deserialize, "reject: reference");
+		return DESERIALIZE_ERR;
+	}
+	/* verbose */
+	/* amend */
+	if (cmd_s->whence != des_s->whence) {
+		set_deserialize_reject_reason("args/whence-changed");
+		trace_printf_key(&trace_deserialize, "reject: whence");
+		return DESERIALIZE_ERR;
+	}
+	/* nowarn */
+	/* use_color */
+	/* no_gettext */
+	/* display_comment_prefix */
+	/* relative_paths */
+	/* submodule_summary */
+
+	/* show_ignored_files - already validated */
+	/* show_untrackes_files - already validated */
+
+	/*
+	 * Submodules are not supported by status serialization.
+	 * The status will not be serialized if it contains submodules,
+	 * and so this check is not needed.
+	 *
+	 * if (my_strcmp_null(cmd_s->ignore_submodule_arg, des_s->ignore_submodule_arg)) {
+	 *	trace_printf_key(&trace_deserialize, "reject: ignore_submodule_arg");
+	 * 	return DESERIALIZE_ERR;
+	 * }
+	 */
+
+	/* color_palette */
+	/* colopts */
+	/* null_termination */
+	/* commit_template */
+	/* show_branch */
+	/* show_stash */
+	/* hints */
+	/* ahead_behind_flags */
+	if (cmd_s->detect_rename != des_s->detect_rename) {
+		set_deserialize_reject_reason("args/detect-rename-changed");
+		trace_printf_key(&trace_deserialize, "reject: detect_rename");
+		return DESERIALIZE_ERR;
+	}
+	if (cmd_s->rename_score != des_s->rename_score) {
+		set_deserialize_reject_reason("args/rename-score-changed");
+		trace_printf_key(&trace_deserialize, "reject: rename_score");
+		return DESERIALIZE_ERR;
+	}
+	if (cmd_s->rename_limit != des_s->rename_limit) {
+		set_deserialize_reject_reason("args/rename-limit-changed");
+		trace_printf_key(&trace_deserialize, "reject: rename_limit");
+		return DESERIALIZE_ERR;
+	}
+	/* status_format */
+	if (!hasheq(cmd_s->sha1_commit, des_s->sha1_commit)) {
+		set_deserialize_reject_reason("args/commit-changed");
+		trace_printf_key(&trace_deserialize, "reject: sha1_commit");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * Copy over display-related fields from the current command.
+	 */
+	des_s->verbose = cmd_s->verbose;
+	/* amend */
+	/* whence */
+	des_s->nowarn = cmd_s->nowarn;
+	des_s->use_color = cmd_s->use_color;
+	des_s->no_gettext = cmd_s->no_gettext;
+	des_s->display_comment_prefix = cmd_s->display_comment_prefix;
+	des_s->relative_paths = cmd_s->relative_paths;
+	des_s->submodule_summary = cmd_s->submodule_summary;
+	memcpy(des_s->color_palette, cmd_s->color_palette,
+	       sizeof(char)*WT_STATUS_MAXSLOT*COLOR_MAXLEN);
+	des_s->colopts = cmd_s->colopts;
+	des_s->null_termination = cmd_s->null_termination;
+	/* commit_template */
+	des_s->show_branch = cmd_s->show_branch;
+	des_s->show_stash = cmd_s->show_stash;
+	/* hints */
+	des_s->ahead_behind_flags = cmd_s->ahead_behind_flags;
+	des_s->status_format = cmd_s->status_format;
+	des_s->fp = cmd_s->fp;
+	if (cmd_s->prefix && *cmd_s->prefix)
+		des_s->prefix = xstrdup(cmd_s->prefix);
+
+	return DESERIALIZE_OK;
+}
+
+static struct cache_time deserialize_prev_mtime = { 0, 0 };
+
+static int try_deserialize_read_from_file_1(const struct wt_status *cmd_s,
+					    const char *path,
+					    struct wt_status *des_s)
+{
+	struct stat st;
+	int result;
+	int fd;
+
+	/*
+	 * If we are spinning waiting for the status cache to become
+	 * valid, skip re-reading it if the mtime has not changed
+	 * since the last time we read it.
+	 */
+	if (lstat(path, &st)) {
+		trace_printf_key(&trace_deserialize,
+				 "could not lstat '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+	if (st.st_mtime == deserialize_prev_mtime.sec &&
+	    ST_MTIME_NSEC(st) == deserialize_prev_mtime.nsec) {
+		trace_printf_key(&trace_deserialize,
+				 "mtime has not changed '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+
+	fd = xopen(path, O_RDONLY);
+	if (fd == -1) {
+		trace_printf_key(&trace_deserialize,
+				 "could not read '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+
+	deserialize_prev_mtime.sec = st.st_mtime;
+	deserialize_prev_mtime.nsec = ST_MTIME_NSEC(st);
+
+	trace_printf_key(&trace_deserialize,
+			 "reading serialization file (%d %d) '%s'",
+			 deserialize_prev_mtime.sec,
+			 deserialize_prev_mtime.nsec,
+			 path);
+
+	result = wt_deserialize_fd(cmd_s, des_s, fd);
+	close(fd);
+
+	return result;
+}
+
+static int try_deserialize_read_from_file(const struct wt_status *cmd_s,
+					  const char *path,
+					  enum wt_status_deserialize_wait dw,
+					  struct wt_status *des_s)
+{
+	int k = 0;
+	int limit;
+	int result = DESERIALIZE_ERR;
+
+	/*
+	 * For "fail" or "no", try exactly once to read the status cache.
+	 * Return an error if the file is stale.
+	 */
+	if (dw == DESERIALIZE_WAIT__FAIL || dw == DESERIALIZE_WAIT__NO) {
+		result = try_deserialize_read_from_file_1(cmd_s, path, des_s);
+		goto done;
+	}
+
+	/*
+	 * Wait for the status cache file to refresh.  Wait duration can
+	 * be in tenths of a second or unlimited.  Poll every 100ms.
+	 */
+	if (dw == DESERIALIZE_WAIT__BLOCK) {
+		/*
+		 * Convert "unlimited" to 1 day.
+		 */
+		limit = 10 * 60 * 60 * 24;
+	} else {
+		/* spin for dw tenths of a second */
+		limit = dw;
+	}
+	for (k = 0; k < limit; k++) {
+		result = try_deserialize_read_from_file_1(
+			cmd_s, path, des_s);
+
+		if (result == DESERIALIZE_OK)
+			break;
+
+		sleep_millisec(100);
+	}
+
+done:
+	trace2_data_string("status", the_repository, "deserialize/path", path);
+	trace2_data_intmax("status", the_repository, "deserialize/polled", k);
+	trace2_data_string("status", the_repository, "deserialize/result",
+			   ((result == DESERIALIZE_OK) ? "ok" : "reject"));
+
+	trace_printf_key(&trace_deserialize,
+			 "wait polled=%d result=%d '%s'",
+			 k, result, path);
+	return result;
+}
+
+/*
+ * Read raw serialized status data from the given file (or STDIN).
+ *
+ * Verify that the args specified in the current command
+ * are compatible with the deserialized data (such as "-uno").
+ *
+ * Copy display-related fields from the current command
+ * into the deserialized data (so that the user can request
+ * long or short as they please).
+ *
+ * Print status report using cached data.
+ */
+int wt_status_deserialize(const struct wt_status *cmd_s,
+			  const char *path,
+			  enum wt_status_deserialize_wait dw)
+{
+	struct wt_status des_s;
+	int result;
+
+	trace2_region_enter("status", "deserialize", the_repository);
+
+	if (path && *path && strcmp(path, "0")) {
+		result = try_deserialize_read_from_file(cmd_s, path, dw, &des_s);
+	} else {
+		trace_printf_key(&trace_deserialize, "reading stdin");
+
+		/*
+		 * Read status cache data from stdin.  Ignore the deserialize-wait
+		 * term, since we cannot read stdin multiple times.
+		 */
+		result = wt_deserialize_fd(cmd_s, &des_s, 0);
+
+		trace2_data_string("status", the_repository, "deserialize/path", "STDIN");
+		trace2_data_string("status", the_repository, "deserialize/result",
+				   ((result == DESERIALIZE_OK) ? "ok" : "reject"));
+	}
+
+	trace2_region_leave("status", "deserialize", the_repository);
+
+	if (result == DESERIALIZE_OK) {
+		wt_status_get_state(cmd_s->repo, &des_s.state, des_s.branch &&
+				    !strcmp(des_s.branch, "HEAD"));
+		wt_status_print(&des_s);
+	}
+
+	return result;
+}
diff --git a/wt-status-serialize.c b/wt-status-serialize.c
new file mode 100644
index 00000000000000..a5f9eea69db9d4
--- /dev/null
+++ b/wt-status-serialize.c
@@ -0,0 +1,337 @@
+#include "cache.h"
+#include "wt-status.h"
+#include "pkt-line.h"
+
+static struct trace_key trace_serialize = TRACE_KEY_INIT(SERIALIZE);
+
+/*
+ * Compute header record for exclude file using format:
+ *      <key> SP <status_char> SP <variant> LF
+ */
+void wt_serialize_compute_exclude_header(struct strbuf *sb,
+					 const char *key,
+					 const char *path)
+{
+	struct stat st;
+	struct stat_data sd;
+
+	memset(&sd, 0, sizeof(sd));
+
+	strbuf_setlen(sb, 0);
+
+	if (!path || !*path) {
+		strbuf_addf(sb, "%s U (unset)", key);
+	} else if (lstat(path, &st) == -1) {
+		if (is_missing_file_error(errno))
+			strbuf_addf(sb, "%s E (not-found) %s", key, path);
+		else
+			strbuf_addf(sb, "%s E (other) %s", key, path);
+	} else {
+		fill_stat_data(&sd, &st);
+		strbuf_addf(sb, "%s F %d %d %s",
+			    key, sd.sd_mtime.sec, sd.sd_mtime.nsec, path);
+	}
+}
+
+static void append_exclude_info(int fd, const char *path, const char *key)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	wt_serialize_compute_exclude_header(&sb, key, path);
+
+	packet_write_fmt(fd, "%s\n", sb.buf);
+
+	strbuf_release(&sb);
+}
+
+static void append_core_excludes_file_info(int fd)
+{
+	/*
+	 * Write pathname and mtime of the core/global excludes file to
+	 * the status cache header.  Since a change in the global excludes
+	 * will/may change the results reported by status, the deserialize
+	 * code should be able to reject the status cache if the excludes
+	 * file changes since when the cache was written.
+	 *
+	 * The "core.excludefile" setting defaults to $XDG_HOME/git/ignore
+	 * and uses a global variable which should have been set during
+	 * wt_status_collect_untracked().
+	 *
+	 * See dir.c:setup_standard_excludes()
+	 */
+	append_exclude_info(fd, excludes_file, "core_excludes");
+}
+
+static void append_repo_excludes_file_info(int fd)
+{
+	/*
+	 * Likewise, there is a per-repo excludes file in .git/info/excludes
+	 * that can change the results reported by status.  And the deserialize
+	 * code needs to be able to reject the status cache if this file
+	 * changes.
+	 *
+	 * See dir.c:setup_standard_excludes() and git_path_info_excludes().
+	 * We replicate the pathname construction here because of the static
+	 * variables/functions used in dir.c.
+	 */
+	char *path = git_pathdup("info/exclude");
+
+	append_exclude_info(fd, path, "repo_excludes");
+
+	free(path);
+}
+
+/*
+ * WARNING: The status cache attempts to preserve the essential in-memory
+ * status data after a status scan into a "serialization" (aka "status cache")
+ * file.  It allows later "git status --deserialize=<foo>" instances to
+ * just print the cached status results without scanning the workdir (and
+ * without reading the index).
+ *
+ * The status cache file is valid as long as:
+ * [1] the set of functional command line options are the same (think "-u").
+ * [2] repo-local and user-global configuration settings are compatible.
+ * [3] nothing in the workdir has changed.
+ *
+ * We rely on:
+ * [1.a] We remember the relevant (functional, non-display) command line
+ *       arguments in the status cache header.
+ * [2.a] We use the mtime of the .git/index to detect staging changes.
+ * [2.b] We use the mtimes of the excludes files to detect changes that
+ *      might affect untracked file reporting.
+ *
+ * But we need external help to verify [3].
+ * [] This includes changes to tracked files.
+ * [] This includes changes to tracked .gitignore files that might change
+ *    untracked file reporting.
+ * [] This includes the creation of new, untracked per-directory .gitignore
+ *    files that might change untracked file reporting.
+ *
+ * [3.a] On GVFS repos, we rely on the GVFS service (mount) daemon to
+ *      watch the filesystem and invalidate (delete) the status cache
+ *      when anything changes inside the workdir.
+ *
+ * [3.b] TODO This problem is not solved for non-GVFS repos.
+ *       [] It is possible that the untracked-cache index extension
+ *          could help with this but that requires status to read the
+ *          index to load the extension.
+ *       [] It is possible that the new fsmonitor facility could also
+ *          provide this information, but that to requires reading the
+ *          index.
+ */
+
+/*
+ * Write V1 header fields.
+ */
+static void wt_serialize_v1_header(struct wt_status *s, int fd)
+{
+	/*
+	 * Write select fields from the current index to help
+	 * the deserializer recognize a stale data set.
+	 */
+	packet_write_fmt(fd, "index_mtime %d %d\n",
+			 s->repo->index->timestamp.sec,
+			 s->repo->index->timestamp.nsec);
+	append_core_excludes_file_info(fd);
+	append_repo_excludes_file_info(fd);
+
+	/*
+	 * Write data from wt_status to qualify this status report.
+	 * That is, if this run specified "-uno", the consumer of
+	 * our serialization should know that.
+	 */
+	packet_write_fmt(fd, "is_initial %d\n", s->is_initial);
+	if (s->branch)
+		packet_write_fmt(fd, "branch %s\n", s->branch);
+	if (s->reference)
+		packet_write_fmt(fd, "reference %s\n", s->reference);
+	/* pathspec */
+	/* verbose */
+	/* amend */
+	packet_write_fmt(fd, "whence %d\n", s->whence);
+	/* nowarn */
+	/* use_color */
+	/* no_gettext */
+	/* display_comment_prefix */
+	/* relative_paths */
+	/* submodule_summary */
+	packet_write_fmt(fd, "show_ignored_mode %d\n", s->show_ignored_mode);
+	packet_write_fmt(fd, "show_untracked_files %d\n", s->show_untracked_files);
+	if (s->ignore_submodule_arg)
+		packet_write_fmt(fd, "ignore_submodule_arg %s\n", s->ignore_submodule_arg);
+	/* color_palette */
+	/* colopts */
+	/* null_termination */
+	/* commit_template */
+	/* show_branch */
+	/* show_stash */
+	packet_write_fmt(fd, "hints %d\n", s->hints);
+	/* ahead_behind_flags */
+	packet_write_fmt(fd, "detect_rename %d\n", s->detect_rename);
+	packet_write_fmt(fd, "rename_score %d\n", s->rename_score);
+	packet_write_fmt(fd, "rename_limit %d\n", s->rename_limit);
+	/* status_format */
+	packet_write_fmt(fd, "sha1_commit %s\n", sha1_to_hex(s->sha1_commit));
+	packet_write_fmt(fd, "committable %d\n", s->committable);
+	packet_write_fmt(fd, "workdir_dirty %d\n", s->workdir_dirty);
+	/* prefix */
+	packet_flush(fd);
+}
+
+/*
+ * Print changed/unmerged items.
+ * We write raw (not c-quoted) pathname(s).  The rename_source is only
+ * set when status computed a rename/copy.
+ *
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allow LFs.
+ */
+static inline void wt_serialize_v1_changed(struct wt_status *s, int fd,
+					   struct string_list_item *item)
+{
+	struct wt_status_change_data *d = item->util;
+	struct wt_status_serialize_data sd;
+	char *begin;
+	char *end;
+	char *p;
+	int len_path, len_rename_source;
+
+	trace_printf_key(&trace_serialize,
+		"change: %d %d %d %d %d %o %o %o %d %d %s %s '%s' '%s'",
+		d->worktree_status,
+		d->index_status,
+		d->stagemask,
+		d->rename_status,
+		d->rename_score,
+		d->mode_head,
+		d->mode_index,
+		d->mode_worktree,
+		d->dirty_submodule,
+		d->new_submodule_commits,
+		oid_to_hex(&d->oid_head),
+		oid_to_hex(&d->oid_index),
+		item->string,
+		(d->rename_source ? d->rename_source : ""));
+
+	sd.fixed.worktree_status       = htonl(d->worktree_status);
+	sd.fixed.index_status          = htonl(d->index_status);
+	sd.fixed.stagemask             = htonl(d->stagemask);
+	sd.fixed.rename_status         = htonl(d->rename_status);
+	sd.fixed.rename_score          = htonl(d->rename_score);
+	sd.fixed.mode_head             = htonl(d->mode_head);
+	sd.fixed.mode_index            = htonl(d->mode_index);
+	sd.fixed.mode_worktree         = htonl(d->mode_worktree);
+	sd.fixed.dirty_submodule       = htonl(d->dirty_submodule);
+	sd.fixed.new_submodule_commits = htonl(d->new_submodule_commits);
+	oidcpy(&sd.fixed.oid_head,  &d->oid_head);
+	oidcpy(&sd.fixed.oid_index, &d->oid_index);
+
+	begin = (char *)&sd;
+	end = begin + sizeof(sd);
+
+	p = sd.variant;
+
+	/*
+	 * Write <path> NUL [<rename_source>] NUL LF at the end of the buffer.
+	 */
+	len_path = strlen(item->string);
+	len_rename_source = d->rename_source ? strlen(d->rename_source) : 0;
+
+	/*
+	 * This is a bit of a hack, but I don't want to split the
+	 * status detail record across multiple pkt-lines.
+	 */
+	if (p + len_path + 1 + len_rename_source + 1 + 1 >= end)
+		BUG("path to long to serialize '%s'", item->string);
+
+	memcpy(p, item->string, len_path);
+	p += len_path;
+	*p++ = '\0';
+
+	if (len_rename_source) {
+		memcpy(p, d->rename_source, len_rename_source);
+		p += len_rename_source;
+	}
+	*p++ = '\0';
+	*p++ = '\n';
+
+	if (packet_write_gently(fd, begin, (p - begin)))
+		BUG("cannot serialize '%s'", item->string);
+}
+
+/*
+ * Write raw (not c-quoted) pathname for an untracked item.
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allows LFs.  That is, deserialization
+ * should use the packet-line length and omit the final LF.
+ */
+static inline void wt_serialize_v1_untracked(struct wt_status *s, int fd,
+					     struct string_list_item *item)
+{
+	packet_write_fmt(fd, "%s\n", item->string);
+}
+
+/*
+ * Write raw (not c-quoted) pathname for an ignored item.
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allows LFs.
+ */
+static inline void wt_serialize_v1_ignored(struct wt_status *s, int fd,
+					   struct string_list_item *item)
+{
+	packet_write_fmt(fd, "%s\n", item->string);
+}
+
+/*
+ * Serialize the list of changes to the given file.  The goal of this
+ * is to just serialize the key fields in wt_status so that a
+ * later command can rebuilt it and do the printing.
+ *
+ * We DO NOT include the contents of wt_status_state NOR
+ * current branch info.  This info easily gets stale and
+ * is relatively quick for the status consumer to compute
+ * as necessary.
+ */
+void wt_status_serialize_v1(int fd, struct wt_status *s)
+{
+	struct string_list_item *iter;
+	int k;
+
+	trace2_region_enter("status", "serialize", the_repository);
+
+	/*
+	 * version header must be first line.
+	 */
+	packet_write_fmt(fd, "version 1\n");
+
+	wt_serialize_v1_header(s, fd);
+
+	if (s->change.nr > 0) {
+		packet_write_fmt(fd, "changed %d\n", s->change.nr);
+		for (k = 0; k < s->change.nr; k++) {
+			iter = &(s->change.items[k]);
+			wt_serialize_v1_changed(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+
+	if (s->untracked.nr > 0) {
+		packet_write_fmt(fd, "untracked %d\n", s->untracked.nr);
+		for (k = 0; k < s->untracked.nr; k++) {
+			iter = &(s->untracked.items[k]);
+			wt_serialize_v1_untracked(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+
+	if (s->ignored.nr > 0) {
+		packet_write_fmt(fd, "ignored %d\n", s->ignored.nr);
+		for (k = 0; k < s->ignored.nr; k++) {
+			iter = &(s->ignored.items[k]);
+			wt_serialize_v1_ignored(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+
+	trace2_region_leave("status", "serialize", the_repository);
+}
diff --git a/wt-status.c b/wt-status.c
index 1f564b12d25995..9024e142475a49 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -18,6 +18,8 @@
 #include "worktree.h"
 #include "lockfile.h"
 
+#define AB_DELAY_WARNING_IN_MS (2 * 1000)
+
 static const char cut_line[] =
 "------------------------ >8 ------------------------\n";
 
@@ -696,6 +698,9 @@ static void wt_status_collect_untracked(struct wt_status *s)
 	if (s->show_untracked_files != SHOW_ALL_UNTRACKED_FILES)
 		dir.flags |=
 			DIR_SHOW_OTHER_DIRECTORIES | DIR_HIDE_EMPTY_DIRECTORIES;
+	if (s->show_untracked_files == SHOW_COMPLETE_UNTRACKED_FILES)
+		dir.flags |= DIR_KEEP_UNTRACKED_CONTENTS;
+
 	if (s->show_ignored_mode) {
 		dir.flags |= DIR_SHOW_IGNORED_TOO;
 
@@ -748,12 +753,23 @@ static int has_unmerged(struct wt_status *s)
 
 void wt_status_collect(struct wt_status *s)
 {
+	trace2_region_enter("status", "worktrees", the_repository);
 	wt_status_collect_changes_worktree(s);
-	if (s->is_initial)
+	trace2_region_leave("status", "worktrees", the_repository);
+
+	if (s->is_initial) {
+		trace2_region_enter("status", "initial", the_repository);
 		wt_status_collect_changes_initial(s);
-	else
+		trace2_region_leave("status", "initial", the_repository);
+	} else {
+		trace2_region_enter("status", "index", the_repository);
 		wt_status_collect_changes_index(s);
+		trace2_region_leave("status", "index", the_repository);
+	}
+
+	trace2_region_enter("status", "untracked", the_repository);
 	wt_status_collect_untracked(s);
+	trace2_region_leave("status", "untracked", the_repository);
 
 	wt_status_get_state(s->repo, &s->state, s->branch && !strcmp(s->branch, "HEAD"));
 	if (s->state.merge_in_progress && !has_unmerged(s))
@@ -1067,14 +1083,29 @@ static void wt_longstatus_print_tracking(struct wt_status *s)
 	struct branch *branch;
 	char comment_line_string[3];
 	int i;
+	uint64_t t_begin = 0;
 
 	assert(s->branch && !s->is_initial);
 	if (!skip_prefix(s->branch, "refs/heads/", &branch_name))
 		return;
 	branch = branch_get(branch_name);
+
+	t_begin = getnanotime();
+
 	if (!format_tracking_info(branch, &sb, s->ahead_behind_flags))
 		return;
 
+	if (advice_status_ahead_behind_warning &&
+	    s->ahead_behind_flags == AHEAD_BEHIND_FULL) {
+		uint64_t t_delta_in_ms = (getnanotime() - t_begin) / 1000000;
+		if (t_delta_in_ms > AB_DELAY_WARNING_IN_MS) {
+			strbuf_addf(&sb, _("\n"
+					   "It took %.2f seconds to compute the branch ahead/behind values.\n"
+					   "You can use '--no-ahead-behind' to avoid this.\n"),
+				    t_delta_in_ms / 1000.0);
+		}
+	}
+
 	i = 0;
 	if (s->display_comment_prefix) {
 		comment_line_string[i++] = comment_line_char;
@@ -2291,6 +2322,13 @@ static void wt_porcelain_v2_print(struct wt_status *s)
 
 void wt_status_print(struct wt_status *s)
 {
+	trace2_data_intmax("status", the_repository, "count/changed", s->change.nr);
+	trace2_data_intmax("status", the_repository, "count/untracked",
+			   s->untracked.nr);
+	trace2_data_intmax("status", the_repository, "count/ignored", s->ignored.nr);
+
+	trace2_region_enter("status", "print", the_repository);
+
 	switch (s->status_format) {
 	case STATUS_FORMAT_SHORT:
 		wt_shortstatus_print(s);
@@ -2308,7 +2346,12 @@ void wt_status_print(struct wt_status *s)
 	case STATUS_FORMAT_LONG:
 		wt_longstatus_print(s);
 		break;
+	case STATUS_FORMAT_SERIALIZE_V1:
+		wt_status_serialize_v1(1, s);
+		break;
 	}
+
+	trace2_region_leave("status", "print", the_repository);
 }
 
 /**
diff --git a/wt-status.h b/wt-status.h
index 3a95975032bb1e..ebc6635484bad9 100644
--- a/wt-status.h
+++ b/wt-status.h
@@ -5,6 +5,7 @@
 #include "string-list.h"
 #include "color.h"
 #include "pathspec.h"
+#include "pkt-line.h"
 #include "remote.h"
 
 struct repository;
@@ -26,7 +27,8 @@ enum color_wt_status {
 enum untracked_status_type {
 	SHOW_NO_UNTRACKED_FILES,
 	SHOW_NORMAL_UNTRACKED_FILES,
-	SHOW_ALL_UNTRACKED_FILES
+	SHOW_ALL_UNTRACKED_FILES,
+	SHOW_COMPLETE_UNTRACKED_FILES,
 };
 
 enum show_ignored_type {
@@ -61,6 +63,7 @@ enum wt_status_format {
 	STATUS_FORMAT_SHORT,
 	STATUS_FORMAT_PORCELAIN,
 	STATUS_FORMAT_PORCELAIN_V2,
+	STATUS_FORMAT_SERIALIZE_V1,
 
 	STATUS_FORMAT_UNSPECIFIED
 };
@@ -158,4 +161,72 @@ int require_clean_work_tree(struct repository *repo,
 			    int ignore_submodules,
 			    int gently);
 
+#define DESERIALIZE_OK  0
+#define DESERIALIZE_ERR 1
+
+struct wt_status_serialize_data_fixed
+{
+	uint32_t worktree_status;
+	uint32_t index_status;
+	uint32_t stagemask;
+	uint32_t rename_status;
+	uint32_t rename_score;
+	uint32_t mode_head;
+	uint32_t mode_index;
+	uint32_t mode_worktree;
+	uint32_t dirty_submodule;
+	uint32_t new_submodule_commits;
+	struct object_id oid_head;
+	struct object_id oid_index;
+};
+
+/*
+ * Consume the maximum amount of data possible in a
+ * packet-line record.  This is overkill because we
+ * have at most 2 relative pathnames, but means we
+ * don't need to allocate a variable length structure.
+ */
+struct wt_status_serialize_data
+{
+	struct wt_status_serialize_data_fixed fixed;
+	char variant[LARGE_PACKET_DATA_MAX
+		     - sizeof(struct wt_status_serialize_data_fixed)];
+};
+
+enum wt_status_deserialize_wait
+{
+	DESERIALIZE_WAIT__UNSET = -3,
+	DESERIALIZE_WAIT__FAIL = -2, /* return error, do not fallback */
+	DESERIALIZE_WAIT__BLOCK = -1, /* unlimited timeout */
+	DESERIALIZE_WAIT__NO = 0, /* immediately fallback */
+	/* any positive value is a timeout in tenths of a second */
+};
+
+/*
+ * Serialize computed status scan results using "version 1" format
+ * to the given file.
+ */
+void wt_status_serialize_v1(int fd, struct wt_status *s);
+
+/*
+ * Deserialize existing status results from the given file and
+ * populate a (new) "struct wt_status".  Use the contents of "cmd_s"
+ * (computed from the command line arguments) to verify that the
+ * cached data is compatible and overlay various display-related
+ * fields.
+ */
+int wt_status_deserialize(const struct wt_status *cmd_s,
+			  const char *path,
+			  enum wt_status_deserialize_wait dw);
+
+int wt_status_deserialize_access(const char *path, int mode);
+
+/*
+ * A helper routine for serialize and deserialize to compute
+ * metadata for the user-global and repo-local excludes files.
+ */
+void wt_serialize_compute_exclude_header(struct strbuf *sb,
+					 const char *key,
+					 const char *path);
+
 #endif /* STATUS_H */