Snabb is an extensible, virtualized, Ethernet networking toolkit. With Snabb you can implement networking applications using the Lua language. Snabb includes all the tools you need to quickly realize your network designs and its really fast too! Furthermore, Snabb is extensible and encourages you to grow the ecosystem to match your requirements.
DIAGRAM: Architecture
+---------------------+
| Your Network Design |
+----*-----*-----*----+
| | |
(Built in and custom Apps and Libraries)
| | |
+-----*-----*-----*-----+
| Snabb Core |
+-----------------------+
The Snabb Core forms a runtime environment (engine) which executes your design. A design is simply a Lua script used to drive the Snabb stack, you can think of it as your top-level "main" routine.
In order to add functionality to the Snabb stack you can load modules into the Snabb engine. These can be Lua modules as well as native code objects. We differentiate between two classes of modules, namely libraries and Apps. Libraries are simple collections of program utilities to be used in your designs, apps or other libraries, just as you might expect. Apps, on the other hand, are code objects that implement a specific interface, which is used by the Snabb engine to organize an App Network.
DIAGRAM: Network
+---------+
| |
+->* Filter0 *--+
| | | |
| +---------+ |
+---+----+ | | +----+---+
| *--+ +->* |
| NIC0 | | NIC1 |
| *<-+ +--* |
+---+----+ | | +----+---+
| +---------+ |
| | | |
+--* Filter1 *<-+
| |
+---------+
Usually, a Snabb design will create a series of apps, interconnect these in a desired way using links and finally pass the resulting app network on to the Snabb engine. The engine's job is to:
- Pump traffic through the app network
- Apply, and inform apps of configuration and link changes
- Report on the network status
The core modules defined below can be loaded using Lua's require. For
example:
local config = require("core.config")
local c = config.new()
...
An app is an isolated implementation of a specific networking function. For example, a switch, a router, or a packet filter.
Apps receive packets on input ports, perform some processing, and transmit packets on output ports. Each app has zero or more input and output ports. For example, a packet filter may have one input and one output port, while a packet recorder may have only an input port. Every app must implement the interface below. Methods which may be left unimplemented are marked as "optional".
— Method myapp:new arg
Required. Create an instance of the app with a given argument arg.
Myapp:new must return an instance of the app. The handling of arg is
up to the app but it is encouraged to use core.config's parse_app_arg
to parse arg.
— Field myapp.input
— Field myapp.output
Tables of named input and output links. These tables are initialized by the engine for use in processing and are read-only.
— Field myapp.appname
Name of the app. Read-only.
— Field myapp.shm
Can be set to a specification for core.shm.create_frame. When set, this field
will be initialized to a frame of shared memory objects by the engine.
— Field myapp.config
Can be set to a specification for core.lib.parse. When set, the specification
will be used to validate the app’s arg when it is configured using
config.app.
— Method myapp:link dir name
Optional. Called during engine.configure() when a link of the app is
added. Unless unlink is specified this method is also called when a link
is removed.
Guaranteed to be called before pull and push are called with new links.
Dir is either 'input' or 'output', and name is the string name
of the link. I.e., the added link can be accessed at self[dir][name].
— Method myapp:unlink dir name
Optional. Called during engine.configure() when a link of the app is
removed.
Dir is either 'input' or 'output', and name is the string name
of the link.
— Method myapp:pull
Optional. Pull packets into the network.
For example: Pull packets from a network adapter into the app network by transmitting them to output ports.
— Method myapp:push
Optional. Push packets through the system.
For example: Move packets from input ports to output ports or to a network adapter.
— Field myapp.push_link
Optional. When specified must be a table of per-link push() methods
that take an input link as an argument. For example an app could specify
a push_link method for its input link foo:
Myapp = { push_link={} }
function Myapp.push_link:foo (input)
while not link.empty(input) do something() end
end
Push_link methods are copied to a fresh table when the app is started,
and it is valid to create push_link methods dynamically during link(),
for example like so:
Myapp = { push_link={} }
function Myapp:link (dir, name)
-- NB: Myapp.push_link ~= self.push_link
if dir == 'input' then
self.push_link[name] = function (self, input)
while not link.empty(input) do something() end
end
end
end
function Myapp:unlink (dir, name)
if dir == 'input' then
self.push_link[name] = nil
end
end
Push is not called when an app has push_link methods for all of its input links. If, however, an app at least one input link without an associated push_link method then push is called in addition to the push_link methods.
— Method myapp:tick
Optional. Called periodically at engine.tick_Hz frequency.
For example: Move packets from input ports to output ports or to a network adapter.
— Method myapp:reconfig arg
Optional. Reconfigure the app with a new arg. If this method is not implemented the app instance is discarded and a new instance is created.
— Method myapp:report
Optional. Print a report of the current app status.
— Method myapp:stop
Optional. Stop the app and release associated external resources.
— Field myapp.zone
Optional. Name of the LuaJIT profiling zone used for this app (descriptive string). The default is the module name.
A config is a description of a packet-processing network. The network is a directed graph. Nodes in the graph are apps that each process packets in a specific way. Each app has a set of named input and output ports—often called rx and tx. Edges of the graph are unidirectional links that carry packets from an output port to an input port.
The config is a purely passive data structure. Creating and
manipulating a config object does not immediately affect operation.
The config has to be activated using engine.configure.
— Function config.new
Creates and returns a new empty configuration.
— Function config.app config, name, class, arg
Adds an app of class with arg to the config where it will be assigned to name.
Example:
config.app(c, "nic", Intel82599, {pciaddr = "0000:00:00.0"})
— Function config.link config, linkspec
Add a link defined by linkspec to the config config. Linkspec must be a string of the format
app_name1.output_port->app_name2.input_port
where app_name1 and app_name2 are names of apps in config and
output_port and input_port are valid output and input ports of the
referenced apps respectively.
Example:
config.link(c, "nic1.tx->nic2.rx")
The engine executes a config by initializing apps, creating links, and
driving the flow of execution. The engine also performs profiling and
reporting functions. It can be reconfigured during runtime. Within Snabb
Switch scripts the core.app module is bound to the global engine
variable.
— Function engine.configure config
Configure the engine to use a new config config. You can safely call this method many times to incrementally update the running app network. The engine updates the app network as follows:
- Apps that did not exist in the old configuration are started.
- Apps that do not exist in the new configuration are stopped. (The app
stop()method is called if defined.) - Apps with unchanged configurations are preserved.
- Apps with changed configurations are updated by calling their
reconfig()method. If thereconfig()method is not implemented then the old instance is stopped a new one started. - Links with unchanged endpoints are preserved.
— Function engine.main options
Run the Snabb engine. Options is a table of key/value pairs. The following keys are recognized:
duration- Duration in seconds to run the engine for (as a floating point number). If this is set you cannot supplydone.done- A function to be called repeatedly byengine.mainuntil it returnstrue. Once it returnstruethe engine will be stopped andengine.mainwill return. If this is set you cannot supplyduration.report- A table which configures the report printed beforeengine.main()returns. The keysshowlinksandshowappscan be set to boolean values to force or suppress link and app reporting individually. By default `engine.main()' will report on links but not on apps.measure_latency- By default, thebreathe()loop is instrumented to record the latency distribution of running the app graph. This information can be processed by thesnabb topprogram. Passingmeasure_latency=falsein the options will disable this instrumentation.no_report- A boolean value. Iftrueno final report will be printed.
— Function engine.stop
Stop all apps in the engine by loading an empty configuration.
— Function engine.now
Returns monotonic time in seconds as a floating point number. Suitable for timers.
— Variable engine.busywait
If set to true then the engine polls continuously for new packets to process. This consumes 100% CPU and makes processing latency less vulnerable to kernel scheduling behavior which can cause pauses of more than one millisecond.
Default: false
— Variable engine.Hz
Frequency at which to poll for new input packets. The default value is 'false' which means to adjust dynamically up to 100us during low traffic. The value can be overridden with a constant integer saying how many times per second to poll.
This setting is not used when engine.busywait is true.
— Variable engine.tick_Hz
Frequency at which to call app:tick methods. The default value is
1000 (call tick()s every millisecond).
A value of 0 effectively disables tick() methods.
A link is a ring buffer used to store packets between apps. Links can be treated either like arrays—accessing their internal structure directly—or as streams of packets by using their API functions.
— Function link.empty link
Predicate used to test if a link is empty. Returns true if link is empty and false otherwise.
— Function link.full link
Predicate used to test if a link is full. Returns true if link is full and false otherwise.
— Function link.nreadable link
Returns the number of packets on link.
— Function link.nwriteable link
Returns the remaining number of packets that fit onto link.
— Function link.receive link
Returns the next available packet (and advances the read cursor) on link. If the link is empty an error is signaled.
— Function link.front link
Return the next available packet without advancing the read cursor on
link. If the link is empty, nil is returned.
— Function link.transmit link, packet
Transmits packet onto link. If the link is full packet is dropped (and the drop counter increased).
— Function link.stats link
Returns a structure holding ring statistics for the link:
txbytes,rxbytes: Counts of transferred bytes.txpackets,rxpackets: Counts of transferred packets.txdrop: Count of packets dropped due to ring overflow.
A packet is an FFI object of type struct packet representing a network
packet that is currently being processed. The packet is used to explicitly
manage the life cycle of the packet. Packets are explicitly allocated and freed
by using packet.allocate and packet.free. When a packet is received using
link.receive its ownership is acquired by the calling app. The app must then
ensure to either transfer the packet ownership to another app by calling
link.transmit on the packet or free the packet using packet.free. Apps may
only use packets they own, e.g. packets that have not been transmitted or
freed. The number of allocatable packets is limited by the size of the
underlying “freelist”, e.g. a pool of unused packet objects from and to which
packets are allocated and freed.
— Type struct packet
struct packet {
uint16_t length;
uint8_t data[packet.max_payload];
};
— Constant packet.max_payload
The maximum payload length of a packet.
— Function packet.allocate
Returns a new empty packet. An an error is raised if there are no packets left
on the freelist. Initially the length of the allocated is 0, and its data
is uninitialized garbage.
— Function packet.free packet
Frees packet and puts in back onto the freelist.
— Function packet.clone packet
Returns an exact copy of packet.
— Function packet.resize packet, length
Sets the payload length of packet, truncating or extending its payload. In the latter case the contents of the extended area at the end of the payload are filled with zeros.
— Function packet.append packet, pointer, length
Appends length bytes starting at pointer to the end of packet. An error is raised if there is not enough space in packet to accomodate length additional bytes.
— Function packet.prepend packet, pointer, length
Prepends length bytes starting at pointer to the front of packet, taking ownership of the packet and returning a new packet. An error is raised if there is not enough space in packet to accomodate length additional bytes.
— Function packet.shiftleft packet, length
Take ownership of packet, truncate it by length bytes from the
front, and return a new packet. Length must be less than or equal to
length of packet.
— Function packet.shiftright packet, length
Take ownership of packet, moves packet payload to the right by
length bytes, growing packet by length. Returns a new packet.
The sum of length and length of packet must be less than or
equal to packet.max_payload.
— Function packet.from_pointer pointer, length
Allocate packet and fill it with length bytes from pointer.
— Function packet.from_string string
Allocate packet and fill it with the contents of string.
— Function packet.account_free packet
Increment internal engine statistics (frees, freebytes, freebits) as if packet were freed, but do not actually put it back onto the freelist.
This function is intended to be used by I/O apps in special cases that need more finegrained control over packet freeing.
— Function packet.free_internal packet
Free packet and put it back onto the freelist, but do not increment internal engine statistics (frees, freebytes, freebits).
See packet.account_free, packet.free.
Snabb allocates special DMA memory that can be accessed directly by network cards. The important characteristic of DMA memory is being located in contiguous physical memory at a stable address.
— Function memory.dma_alloc bytes, [alignment]
Returns a pointer to bytes of new DMA memory.
Optionally a specific alignment requirement can be provided (in bytes). The default alignment is 128.
— Function memory.virtual_to_physical pointer
Returns the physical address (uint64_t) the DMA memory at pointer.
— Variable memory.huge_page_size
Size of a single huge page in bytes. Read-only.
This module facilitates creation and management of named shared memory objects.
Objects can be created using shm.create similar to ffi.new, except that
separate calls to shm.open for the same name will each return a new mapping
of the same shared memory. Different processes can share memory by mapping an
object with the same name (and type). Each process can map any object any
number of times.
Mappings are deleted on process termination or with an explicit shm.unmap.
Names are unlinked from objects that are no longer needed using shm.unlink.
Object memory is freed when the name is unlinked and all mappings have been
deleted.
Names can be fully qualified or abbreviated to be within the current process.
Here are examples of names and how they are resolved where <pid> is the PID
of this process:
- Local:
foo/bar⇒/var/run/snabb/<pid>/foo/bar - Fully qualified:
/1234/foo/bar⇒/var/run/snabb/1234/foo/bar
Behind the scenes the objects are backed by files on ram disk
(/var/run/snabb/<pid>) and accessed with the equivalent of POSIX
shared memory (shm_overview(7)). The files are automatically removed
on shutdown unless the environment SNABB_SHM_KEEP is set. The
location /var/run/snabb can be overridden by the environment
variable SNABB_SHM_ROOT.
Shared memory objects are created world-readable for convenient access
by diagnostic tools. You can lock this down by setting
SNABB_SHM_ROOT to a path under a directory with appropriate
permissions.
The practical limit on the number of objects that can be mapped will depend on the operating system limit for memory mappings. On Linux the default limit is 65,530 mappings:
$ sysctl vm.max_map_count vm.max_map_count = 65530
— Function shm.create name, type
Creates and maps a shared object of type into memory via a hierarchical name. Returns a pointer to the mapped object.
— Function shm.open name, type, [readonly]
Maps an existing shared object of type into memory via a hierarchical name. If readonly is non-nil the shared object is mapped in read-only mode. Readonly defaults to nil. Fails if the shared object does not already exist. Returns a pointer to the mapped object.
— Function shm.alias new-path existing-path
Create an alias (symbolic link) for an object.
— Function shm.path name
Returns the fully-qualified path for an object called name.
— Function shm.exists name
Returns a true value if shared object by name exists.
— Function shm.unmap pointer
Deletes the memory mapping for pointer.
— Function shm.unlink path
Unlinks the subtree of objects designated by path from the filesystem.
— Function shm.children path
Returns an array of objects in the directory designated by path.
— Function shm.register type, module
Registers an abstract shared memory object type implemented by module in
shm.types. Module must provide the following functions:
- create name, ...
- open, name
and can optionally provide the function:
- delete, name
The module’s type variable must be bound to type. To register a new type
a module might invoke shm.register like so:
type = shm.register('mytype', getfenv())
-- Now the following holds true:
-- shm.types[type] == getfenv()
— Variable shm.types
A table that maps types to modules. See shm.register.
— Function shm.create_frame path, specification
Creates and returns a shared memory frame by specification under path. A frame is a table of mapped—possibly abstract‑shared memory objects. Specification must be of the form:
{ <name> = {<module>, ...},
... }
Module must implement an abstract type registered with shm.register, and is
followed by additional initialization arguments to its create function.
Example usage:
local counter = require("core.counter")
-- Create counters foo/bar/{dtime,rxpackets,txpackets}.counter
local f = shm.create_frame(
"foo/bar",
{dtime = {counter, C.get_unix_time()},
rxpackets = {counter},
txpackets = {counter}})
counter.add(f.rxpackets)
counter.read(f.dtime)
— Function shm.open_frame path
Opens and returns the shared memory frame under path for reading.
— Function shm.delete_frame frame
Deletes/unmaps a shared memory frame. The frame directory is unlinked if
frame was created by shm.create_frame.
Double-buffered shared memory counters. Counters are 64-bit unsigned values.
Registered with core.shm as type counter.
— Function counter.create name, [initval]
Creates and returns a counter by name, initialized to initval. Initval
defaults to 0.
— Function counter.open name
Opens and returns the counter by name for reading.
— Function counter.delete name
Deletes and unmaps the counter by name.
— Function counter.commit
Commits buffered counter values to public shared memory.
— Function counter.set counter, value
Sets counter to value.
— Function counter.add counter, [value]
Increments counter by value. Value defaults to 1.
— Function counter.read counter
Returns the value of counter.
Shared memory histogram with logarithmic buckets. Registered with core.shm as
type histogram.
— Function histogram.new min, max
Returns a new histogram, with buckets covering the range from min to max.
The range between min and max will be divided logarithmically.
— Function histogram.create name, min, max
Creates and returns a histogram as in histogram.new by name. If the file
exists already, it will be cleared.
— Function histogram.open name
Opens and returns histogram by name for reading.
— Method histogram:add measurement
Adds measurement to histogram.
— Method histogram:iterate prev
When used as for count, lo, hi in histogram:iterate(), visits all buckets in
histogram in order from lowest to highest. Count is the number of samples
recorded in that bucket, and lo and hi are the lower and upper bounds of
the bucket. Note that count is an unsigned 64-bit integer; to get it as a Lua
number, use tonumber.
If prev is given, it should be a snapshot of the previous version of the histogram. In that case, the count values will be returned as a difference between their values in histogram and their values in prev.
— Method histogram:snapshot [dest]
Copies out the contents of histogram into the histogram dest and returns
dest. If dest is not given, the result will be a fresh histogram.
— Method histogram:clear
Clears the buckets of histogram.
— Method *histogram:wrap_thunk thunk, now
Returns a closure that wraps thunk, measuring and recording the difference between calls to now before and after thunk into histogram.
— Method *histogram:summarize prev
Returns the approximate minimum, average, and maximum values recorded in histogram.
If prev is given, it should be a snapshot of a previous version of the histogram. In that case, this method returns the approximate minimum, average and maximum values for the difference between histogram and prev.
The core.lib module contains miscellaneous utilities.
— Function lib.equal x, y
Predicate to test if x and y are structurally similar (isomorphic).
— Function lib.can_open filename, mode
Predicate to test if file at filename can be successfully opened with mode.
— Function lib.can_read filename
Predicate to test if file at filename can be successfully opened for reading.
— Function lib.can_write filename
Predicate to test if file at filename can be successfully opened for writing.
— Function lib.readcmd command, what
Runs Unix shell command and returns what of its output. What must
be a valid argument to file:read.
— Function lib.readfile filename, what
Reads and returns what from file at filename. What must be a valid
argument to file:read.
— Function lib.writefile filename, value
Writes value to file at filename using file:write. Returns the
value returned by file:write.
— Function lib.readlink filename
Returns the true name of symbolic link at filename.
— Function lib.dirname filename
Returns the dirname(3) of filename.
— Function lib.basename filename
Returns the basename(3) of filename.
— Function lib.firstfile directory
Returns the filename of the first file in directory.
— Function lib.firstline filename
Returns the first line of file at filename as a string.
— Function lib.load_string string
Evaluates and returns the value of the Lua expression in string.
— Function lib.load_conf filename
Evaluates and returns the value of the Lua expression in file at filename.
— Function lib.store_conf filename, value
Writes value to file at filename as a Lua expression. Supports
tables, strings and everything that can be readably printed using
print.
— Function lib.bits bitset, basevalue
Returns a bitmask using the values of bitset as indexes. The keys of bitset are ignored (and can be used as comments).
Example:
bits({RESET=0,ENABLE=4}, 123) => 1<<0 | 1<<4 | 123
— Function lib.bitset value, n
Predicate to test if bit number n of value is set.
— Function lib.bitfield size, struct, member, offset, nbits, value
Combined accesor and setter function for bit ranges of integers in cdata structs. Sets nbits (number of bits) starting from offset to value. If value is not given the current value is returned.
Size may be one of 8, 16 or 32 depending on the bit size of the integer being set or read.
Struct must be a pointer to a cdata object and member must be the literal name of a member of struct.
Example:
local struct_t = ffi.typeof[[struct { uint16_t flags; }]]
-- Assuming `s' is an instance of `struct_t', set bits 4-7 to 0xF:
lib.bitfield(16, s, 'flags', 4, 4, 0xf)
-- Get the value:
lib.bitfield(16, s, 'flags', 4, 4) -- => 0xF
— Function string:split pattern
Returns an iterator over the string split by pattern. Pattern must be
a valid argument to string:gmatch.
Example:
for word, sep in ("foo!bar!baz"):split("(!)") do
print(word, sep)
end
> foo !
> bar !
> baz nil
— Function lib.hexdump string
Returns hexadecimal string for bytes in string.
— Function lib.hexundump hexstring, n, error
Returns string of n bytes for hexstring. Throws an error if less than n
hex-encoded bytes could be parsed unless error is false.
Error is optional and can be the error message to throw.
— Function lib.comma_value n
Returns a string for decimal number n with magnitudes separated by commas. Example:
comma_value(1000000) => "1,000,000"
— Function lib.random_bytes_from_dev_urandom length
Return length bytes of random data, as a byte array, taken from
/dev/urandom. Suitable for cryptographic usage.
— Function lib.random_bytes_from_math_random length
Return length bytes of random data, as a byte array, where each byte
was taken from math.random(0, 255). Not suitable for cryptographic
usage.
— Function lib.random_bytes length — Function lib.randomseed seed
Initialize Snabb's random number generation facility. If seed is nil,
then the Lua math.random() function will be seeded from
/dev/urandom, and lib.random_bytes will be initialized to
lib.random_bytes_from_dev_urandom. This is Snabb's default mode of
operation.
Sometimes it's useful to make Snabb use deterministic random numbers.
In that case, pass a seed to lib.randomseed; Snabb will set
lib.random_bytes to lib.random_bytes_from_math_random, and also
print out a message to stderr indicating that we are using lower-quality
deterministic random numbers.
As part of its initialization process, Snabb will call lib.randomseed
with the value of the SNABB_RANDOM_SEED environment variable (if
any). Set this environment variable to enable deterministic random
numbers.
— Function lib.bounds_checked type, base, offset, size
Returns a table that acts as a bounds checked wrapper around a C array of
type and size starting at base plus offset. Type must be a
ctype and the caller must ensure that the allocated memory region at
base/offset is at least sizeof(type)*size bytes long.
— Function lib.throttle seconds
Return a closure that returns true at most once during any seconds
(a floating point value) time interval, otherwise false.
— Function lib.timeout seconds
Returns a closure that returns true if seconds (a floating point
value) have elapsed since it was created, otherwise false.
— Function lib.waitfor condition
Blocks until the function condition returns a true value.
— Function lib.waitfor2 name, condition, attempts, interval
Repeatedly calls the function condition in interval
(milliseconds). If condition returns a true value waitfor2
returns. If condition does not return a true value after attempts
waitfor2 raises an error identified by name.
— Function lib.yesno flag
Returns the string "yes" if flag is a true value and "no"
otherwise.
— Function lib.align value, size
Return the next integer that is a multiple of size starting from value.
— Function lib.csum pointer, length
Computes and returns the "IP checksum" length bytes starting at pointer.
— Function lib.update_csum pointer, length, checksum
Returns checksum updated by length bytes starting at
pointer. The default of checksum is 0LL.
— Function lib.finish_csum checksum
Returns the finalized checksum.
— Function lib.malloc etype
Returns a pointer to newly allocated DMA memory for etype.
— Function lib.deepcopy object
Returns a copy of object. Supports tables as well as ctypes.
— Function lib.array_copy array
Returns a copy of array. Array must not be a "sparse array".
— Function lib.htonl n
— Function lib.htons n
Host to network byte order conversion functions for 32 and 16 bit integers n respectively. Unsigned.
— Function lib.ntohl n
— Function lib.ntohs n
Network to host byte order conversion functions for 32 and 16 bit integers n respectively. Unsigned.
— Function lib.random_bytes count
Return a fresh array of count random bytes. Suitable for cryptographic usage.
— Function lib.parse arg, config
Validates arg against the specification in config, and returns a fresh
table containing the parameters in arg and any omitted optional parameters
with their default values. Given arg, a table of parameters or nil, assert
that from config all of the required keys are present, fill in any missing
values for optional keys, and error if any unknown keys are found. Config has
the following format:
config := { key = {[required=boolean], [default=value]}, ... }
Each key is optional unless required is set to a true value, and its default
value defaults to nil.
Example:
lib.parse({foo=42, bar=43}, {foo={required=true}, bar={}, baz={default=44}})
=> {foo=42, bar=43, baz=44}
- Function lib.set vargs
Reads a variable number of arguments and returns a table representing a set. The returned value can be used to query whether an element belongs or not to the set.
Example:
local t = set('foo', 'bar')
t['foo'] -- yields true.
t['quax'] -- yields false.
Snabb can operate as a group of cooperating processes. The main
process is the initial one that you start directly. The optional
worker processes are children spawned when the main process calls
the core.worker module.
DIAGRAM: Multiprocessing
+----------+
+-------+ Main +-------+
| +----------+ |
: : :
+-----+----+ +----+-----+ +----+-----+
| worker 1 | : .... | | worker N |
+----------+ +----------+ +----------+
Each worker is a complete Snabb process. They can define app networks, run the engine, and do everything else that ordinary Snabb processes do. The exact behavior of each worker is determined by a Lua expression provided upon creation.
Groups of Snabb processes each have the following special properties:
- Group termination: Terminating the main process automatically terminates all of the
workers. This works for all process termination scenarios including
kill -9. - Shared DMA memory: DMA memory pointers obtained with
memory.dma_alloc()are usable by all processes in the group. This means that you can share DMA memory pointers between processes, for example viashmshared memory objects, and reference them from any process. (The memory is automatically mapped at the expected address via aSEGVsignal handler.) - PCI device shutdown: For each PCI device opened by a process within the group, bus mastering (DMA) is disabled upon termination before any DMA memory is returned to the kernel. This prevents "dangling" DMA requests from corrupting memory that has been freed and reused. See lib.hardware.pci for details.
The core.worker API functions are available in the main process only:
— Function worker.start name luacode
Start a named worker process. The worker starts with a completely
fresh Snabb process image (fork()+execve()) and then executes the
string luacode as a Lua source code expression.
Example:
worker.start("myworker", [[
print("hello world, from a Snabb worker process!")
print("could configure and run the engine now...")
]])
— Function worker.stop name
Stop a named worker process. The worker is abruptly killed.
Example:
worker.stop("myworker")
— Function worker.status
Return a table summarizing the status of all workers. The table key is
the worker name and the value is a table with pid and alive
attributes.
Example:
for w, s in pairs(worker.status()) do
print((" worker %s: pid=%s alive=%s"):format(
w, s.pid, s.alive))
end
Output:
worker w3: pid=21949 alive=true
worker w1: pid=21947 alive=true
worker w2: pid=21948 alive=true
Snabb designs can be run either with:
snabb <snabb-arg>* <design> <design-arg>*
or
#!/usr/bin/env snabb <snabb-arg>*
...
The main module provides an interface for running Snabb scripts. It exposes various operating system functions to scripts.
— Field main.parameters
A list of command-line arguments to the running script. Read-only.
— Function main.exit status
Cleanly exits the process with status.