Merge connect_from_config into connect with optional arguments

Existing code which calls `Block.connect path` will still work.

New code can now request different behaviour by supplying the optional
arguments ?buffered and ?sync.

Signed-off-by: David Scott <[email protected]>

lib/block.ml

@@ -178,9 +178,11 @@ let remove_prefix prefix x =
   then true, String.sub x prefix' (x' - prefix')
   else false, x
 
-let connect name =
-  let buffered, path = remove_prefix buffered_prefix name in
-  let config = { Config.buffered; sync = false; path } in
+let connect ?buffered ?sync name =
+  let legacy_buffered, path = remove_prefix buffered_prefix name in
+  (* Keep support for the legacy buffered: prefix until version 3.x.y *)
+  let buffered = if legacy_buffered then Some true else buffered in
+  let config = Config.create ?buffered ?sync name in
   connect_from_config config
 
 let disconnect t = match t.fd with

lib/block.mli

@@ -32,8 +32,6 @@ val blkgetsize: string -> Unix.file_descr -> [ `Ok of int64 | `Error of error ]
     given by [fd]. [path] is only used to construct a human-readable error
     message. *)
 
-val connect : string -> [`Ok of t | `Error of error] io
-
 module Config: sig
   type t = {
     buffered: bool; (** true if I/O hits the OS disk caches, false if "direct" *)
@@ -54,9 +52,11 @@ module Config: sig
   (** Parse the result of a previous [to_string] invocation *)
 end
 
-val connect_from_config : Config.t -> [`Ok of t | `Error of error] io
-(** [connect_from_config config] connects to the block device described by
-    [config]. *)
+val connect : ?buffered:bool -> ?sync:bool -> string -> [`Ok of t | `Error of error] io
+(** [connect ?buffered ?sync path] connects to a block device on the filesystem
+    at [path]. By default I/O is unbuffered and fully synchronous. These defaults
+    can be changed by supplying the optional arguments [~buffered:true] and
+    [~sync:false] *)
 
 val resize : t -> int64 -> [ `Ok of unit | `Error of error ] io
 (** [resize t new_size_sectors] attempts to resize the connected device