Add an experimental built-in FSMonitor

.gitignore

@@ -71,6 +71,7 @@
 /git-format-patch
 /git-fsck
 /git-fsck-objects
+/git-fsmonitor--daemon
 /git-gc
 /git-get-tar-commit-id
 /git-grep

Documentation/config/core.txt

@@ -66,18 +66,45 @@ core.fsmonitor::
 	will identify all files that may have changed since the
 	requested date/time. This information is used to speed up git by
 	avoiding unnecessary processing of files that have not changed.
-	See the "fsmonitor-watchman" section of linkgit:githooks[5].
++
+See the "fsmonitor-watchman" section of linkgit:githooks[5].
++
+Note: FSMonitor hooks (and this config setting) are ignored if the
+(experimental) built-in FSMonitor is enabled (see
+`core.useBuiltinFSMonitor`).
 
 core.fsmonitorHookVersion::
-	Sets the version of hook that is to be used when calling fsmonitor.
-	There are currently versions 1 and 2. When this is not set,
-	version 2 will be tried first and if it fails then version 1
-	will be tried. Version 1 uses a timestamp as input to determine
-	which files have changes since that time but some monitors
-	like watchman have race conditions when used with a timestamp.
-	Version 2 uses an opaque string so that the monitor can return
-	something that can be used to determine what files have changed
-	without race conditions.
+	Sets the version of hook that is to be used when calling the
+	FSMonitor hook (as configured via `core.fsmonitor`).
++
+There are currently versions 1 and 2. When this is not set,
+version 2 will be tried first and if it fails then version 1
+will be tried. Version 1 uses a timestamp as input to determine
+which files have changes since that time but some monitors
+like watchman have race conditions when used with a timestamp.
+Version 2 uses an opaque string so that the monitor can return
+something that can be used to determine what files have changed
+without race conditions.
++
+Note: FSMonitor hooks (and this config setting) are ignored if the
+built-in FSMonitor is enabled (see `core.useBuiltinFSMonitor`).
+
+core.useBuiltinFSMonitor::
+	(EXPERIMENTAL) If set to true, enable the built-in filesystem
+	event watcher (for technical details, see
+	linkgit:git-fsmonitor--daemon[1]).
++
+Like external (hook-based) FSMonitors, the built-in FSMonitor can speed up
+Git commands that need to refresh the Git index (e.g. `git status`) in a
+worktree with many files. The built-in FSMonitor facility eliminates the
+need to install and maintain an external third-party monitoring tool.
++
+The built-in FSMonitor is currently available only on a limited set of
+supported platforms.
++
+Note: if this config setting is set to `true`, any FSMonitor hook
+configured via `core.fsmonitor` (and possibly `core.fsmonitorHookVersion`)
+is ignored.
 
 core.trustctime::
 	If false, the ctime differences between the index and the

Documentation/git-fsmonitor--daemon.txt

@@ -0,0 +1,107 @@
+git-fsmonitor--daemon(1)
+========================
+
+NAME
+----
+git-fsmonitor--daemon - (EXPERIMENTAL) Builtin file system monitor daemon
+
+SYNOPSIS
+--------
+[verse]
+'git fsmonitor--daemon' --start
+'git fsmonitor--daemon' --run
+'git fsmonitor--daemon' --stop
+'git fsmonitor--daemon' --is-running
+'git fsmonitor--daemon' --is-supported
+'git fsmonitor--daemon' --query <token>
+'git fsmonitor--daemon' --query-index
+'git fsmonitor--daemon' --flush
+
+DESCRIPTION
+-----------
+
+NOTE! This command is still only an experiment, subject to change dramatically
+(or even to be abandoned).
+
+Monitors files and directories in the working directory for changes using
+platform-specific file system notification facilities.
+
+It communicates directly with commands like `git status` using the
+link:technical/api-simple-ipc.html[simple IPC] interface instead of
+the slower linkgit:githooks[5] interface.
+
+OPTIONS
+-------
+
+--start::
+	Starts the fsmonitor daemon in the background.
+
+--run::
+	Runs the fsmonitor daemon in the foreground.
+
+--stop::
+	Stops the fsmonitor daemon running for the current working
+	directory, if present.
+
+--is-running::
+	Exits with zero status if the fsmonitor daemon is watching the
+	current working directory.
+
+--is-supported::
+	Exits with zero status if the fsmonitor daemon feature is supported
+	on this platform.
+
+--query <token>::
+	Connects to the fsmonitor daemon (starting it if necessary) and
+	requests the list of changed files and directories since the
+	given token.
+	This is intended for testing purposes.
+
+--query-index::
+	Read the current `<token>` from the File System Monitor index
+	extension (if present) and use it to query the fsmonitor daemon.
+	This is intended for testing purposes.
+
+--flush::
+	Force the fsmonitor daemon to flush its in-memory cache and
+	re-sync with the file system.
+	This is intended for testing purposes.
+
+REMARKS
+-------
+The fsmonitor daemon is a long running process that will watch a single
+working directory.  Commands, such as `git status`, should automatically
+start it (if necessary) when `core.useBuiltinFSMonitor` is set to `true`
+(see linkgit:git-config[1]).
+
+Configure the built-in FSMonitor via `core.useBuiltinFSMonitor` in each
+working directory separately, or globally via `git config --global
+core.useBuiltinFSMonitor true`.
+
+Tokens are opaque strings.  They are used by the fsmonitor daemon to
+mark a point in time and the associated internal state.  Callers should
+make no assumptions about the content of the token.  In particular,
+the should not assume that it is a timestamp.
+
+Query commands send a request-token to the daemon and it responds with
+a summary of the changes that have occurred since that token was
+created.  The daemon also returns a response-token that the client can
+use in a future query.
+
+For more information see the "File System Monitor" section in
+linkgit:git-update-index[1].
+
+CAVEATS
+-------
+
+The fsmonitor daemon does not currently know about submodules and does
+not know to filter out file system events that happen within a
+submodule.  If fsmonitor daemon is watching a super repo and a file is
+modified within the working directory of a submodule, it will report
+the change (as happening against the super repo).  However, the client
+should properly ignore these extra events, so performance may be affected
+but it should not cause an incorrect result.
+
+GIT
+---
+Part of the linkgit:git[1] suite

Documentation/git-update-index.txt

@@ -498,7 +498,9 @@ FILE SYSTEM MONITOR
 This feature is intended to speed up git operations for repos that have
 large working directories.
 
-It enables git to work together with a file system monitor (see the
+It enables git to work together with a file system monitor (see
+linkgit:git-fsmonitor--daemon[1]
+and the
 "fsmonitor-watchman" section of linkgit:githooks[5]) that can
 inform it as to what files have been modified. This enables git to avoid
 having to lstat() every file to find modified files.

Documentation/githooks.txt

@@ -584,7 +584,8 @@ fsmonitor-watchman
 
 This hook is invoked when the configuration option `core.fsmonitor` is
 set to `.git/hooks/fsmonitor-watchman` or `.git/hooks/fsmonitor-watchmanv2`
-depending on the version of the hook to use.
+depending on the version of the hook to use, unless overridden via
+`core.useBuiltinFSMonitor` (see linkgit:git-config[1]).
 
 Version 1 takes two arguments, a version (1) and the time in elapsed
 nanoseconds since midnight, January 1, 1970.

Documentation/technical/api-simple-ipc.txt

@@ -0,0 +1,105 @@
+Simple-IPC API
+==============
+
+The Simple-IPC API is a collection of `ipc_` prefixed library routines
+and a basic communication protocol that allow an IPC-client process to
+send an application-specific IPC-request message to an IPC-server
+process and receive an application-specific IPC-response message.
+
+Communication occurs over a named pipe on Windows and a Unix domain
+socket on other platforms.  IPC-clients and IPC-servers rendezvous at
+a previously agreed-to application-specific pathname (which is outside
+the scope of this design) that is local to the computer system.
+
+The IPC-server routines within the server application process create a
+thread pool to listen for connections and receive request messages
+from multiple concurrent IPC-clients.  When received, these messages
+are dispatched up to the server application callbacks for handling.
+IPC-server routines then incrementally relay responses back to the
+IPC-client.
+
+The IPC-client routines within a client application process connect
+to the IPC-server and send a request message and wait for a response.
+When received, the response is returned back the caller.
+
+For example, the `fsmonitor--daemon` feature will be built as a server
+application on top of the IPC-server library routines.  It will have
+threads watching for file system events and a thread pool waiting for
+client connections.  Clients, such as `git status` will request a list
+of file system events since a point in time and the server will
+respond with a list of changed files and directories.  The formats of
+the request and response are application-specific; the IPC-client and
+IPC-server routines treat them as opaque byte streams.
+
+
+Comparison with sub-process model
+---------------------------------
+
+The Simple-IPC mechanism differs from the existing `sub-process.c`
+model (Documentation/technical/long-running-process-protocol.txt) and
+used by applications like Git-LFS.  In the LFS-style sub-process model
+the helper is started by the foreground process, communication happens
+via a pair of file descriptors bound to the stdin/stdout of the
+sub-process, the sub-process only serves the current foreground
+process, and the sub-process exits when the foreground process
+terminates.
+
+In the Simple-IPC model the server is a very long-running service.  It
+can service many clients at the same time and has a private socket or
+named pipe connection to each active client.  It might be started
+(on-demand) by the current client process or it might have been
+started by a previous client or by the OS at boot time.  The server
+process is not associated with a terminal and it persists after
+clients terminate.  Clients do not have access to the stdin/stdout of
+the server process and therefore must communicate over sockets or
+named pipes.
+
+
+Server startup and shutdown
+---------------------------
+
+How an application server based upon IPC-server is started is also
+outside the scope of the Simple-IPC design and is a property of the
+application using it.  For example, the server might be started or
+restarted during routine maintenance operations, or it might be
+started as a system service during the system boot-up sequence, or it
+might be started on-demand by a foreground Git command when needed.
+
+Similarly, server shutdown is a property of the application using
+the simple-ipc routines.  For example, the server might decide to
+shutdown when idle or only upon explicit request.
+
+
+Simple-IPC protocol
+-------------------
+
+The Simple-IPC protocol consists of a single request message from the
+client and an optional response message from the server.  Both the
+client and server messages are unlimited in length and are terminated
+with a flush packet.
+
+The pkt-line routines (Documentation/technical/protocol-common.txt)
+are used to simplify buffer management during message generation,
+transmission, and reception.  A flush packet is used to mark the end
+of the message.  This allows the sender to incrementally generate and
+transmit the message.  It allows the receiver to incrementally receive
+the message in chunks and to know when they have received the entire
+message.
+
+The actual byte format of the client request and server response
+messages are application specific.  The IPC layer transmits and
+receives them as opaque byte buffers without any concern for the
+content within.  It is the job of the calling application layer to
+understand the contents of the request and response messages.
+
+
+Summary
+-------
+
+Conceptually, the Simple-IPC protocol is similar to an HTTP REST
+request.  Clients connect, make an application-specific and
+stateless request, receive an application-specific
+response, and disconnect.  It is a one round trip facility for
+querying the server.  The Simple-IPC routines hide the socket,
+named pipe, and thread pool details and allow the application
+layer to focus on the application at hand.

Makefile

@@ -464,6 +464,11 @@ all::
 # directory, and the JSON compilation database 'compile_commands.json' will be
 # created at the root of the repository.
 #
+# If your platform supports an built-in fsmonitor backend, set
+# FSMONITOR_DAEMON_BACKEND to the name of the corresponding
+# `compat/fsmonitor/fsmonitor-fs-listen-<name>.c` that implements the
+# `fsmonitor_fs_listen__*()` routines.
+#
 # Define DEVELOPER to enable more compiler warnings. Compiler version
 # and family are auto detected, but could be overridden by defining
 # COMPILER_FEATURES (see config.mak.dev). You can still set
@@ -736,6 +741,7 @@ TEST_BUILTINS_OBJS += test-serve-v2.o
 TEST_BUILTINS_OBJS += test-sha1.o
 TEST_BUILTINS_OBJS += test-sha256.o
 TEST_BUILTINS_OBJS += test-sigchain.o
+TEST_BUILTINS_OBJS += test-simple-ipc.o
 TEST_BUILTINS_OBJS += test-strcmp-offset.o
 TEST_BUILTINS_OBJS += test-string-list.o
 TEST_BUILTINS_OBJS += test-submodule-config.o
@@ -882,6 +888,7 @@ LIB_OBJS += fetch-pack.o
 LIB_OBJS += fmt-merge-msg.o
 LIB_OBJS += fsck.o
 LIB_OBJS += fsmonitor.o
+LIB_OBJS += fsmonitor-ipc.o
 LIB_OBJS += gettext.o
 LIB_OBJS += gpg-interface.o
 LIB_OBJS += graph.o
@@ -1081,6 +1088,7 @@ BUILTIN_OBJS += builtin/fmt-merge-msg.o
 BUILTIN_OBJS += builtin/for-each-ref.o
 BUILTIN_OBJS += builtin/for-each-repo.o
 BUILTIN_OBJS += builtin/fsck.o
+BUILTIN_OBJS += builtin/fsmonitor--daemon.o
 BUILTIN_OBJS += builtin/gc.o
 BUILTIN_OBJS += builtin/get-tar-commit-id.o
 BUILTIN_OBJS += builtin/grep.o
@@ -1667,6 +1675,14 @@ ifdef NO_UNIX_SOCKETS
 	BASIC_CFLAGS += -DNO_UNIX_SOCKETS
 else
 	LIB_OBJS += unix-socket.o
+	LIB_OBJS += unix-stream-server.o
+	LIB_OBJS += compat/simple-ipc/ipc-shared.o
+	LIB_OBJS += compat/simple-ipc/ipc-unix-socket.o
+endif
+
+ifdef USE_WIN32_IPC
+	LIB_OBJS += compat/simple-ipc/ipc-shared.o
+	LIB_OBJS += compat/simple-ipc/ipc-win32.o
 endif
 
 ifdef NO_ICONV
@@ -1881,6 +1897,11 @@ ifdef NEED_ACCESS_ROOT_HANDLER
 	COMPAT_OBJS += compat/access.o
 endif
 
+ifdef FSMONITOR_DAEMON_BACKEND
+	COMPAT_CFLAGS += -DHAVE_FSMONITOR_DAEMON_BACKEND
+	COMPAT_OBJS += compat/fsmonitor/fsmonitor-fs-listen-$(FSMONITOR_DAEMON_BACKEND).o
+endif
+
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK = NoThanks
 endif
@@ -2731,6 +2752,9 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo PAGER_ENV=\''$(subst ','\'',$(subst ','\'',$(PAGER_ENV)))'\' >>$@+
 	@echo DC_SHA1=\''$(subst ','\'',$(subst ','\'',$(DC_SHA1)))'\' >>$@+
 	@echo X=\'$(X)\' >>$@+
+ifdef FSMONITOR_DAEMON_BACKEND
+	@echo FSMONITOR_DAEMON_BACKEND=\''$(subst ','\'',$(subst ','\'',$(FSMONITOR_DAEMON_BACKEND)))'\' >>$@+
+endif
 ifdef TEST_OUTPUT_DIRECTORY
 	@echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@+
 endif

builtin.h

@@ -158,6 +158,7 @@ int cmd_for_each_ref(int argc, const char **argv, const char *prefix);
 int cmd_for_each_repo(int argc, const char **argv, const char *prefix);
 int cmd_format_patch(int argc, const char **argv, const char *prefix);
 int cmd_fsck(int argc, const char **argv, const char *prefix);
+int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix);
 int cmd_gc(int argc, const char **argv, const char *prefix);
 int cmd_get_tar_commit_id(int argc, const char **argv, const char *prefix);
 int cmd_grep(int argc, const char **argv, const char *prefix);

builtin/credential-cache--daemon.c

@@ -203,9 +203,10 @@ static int serve_cache_loop(int fd)
 
 static void serve_cache(const char *socket_path, int debug)
 {
+	struct unix_stream_listen_opts opts = UNIX_STREAM_LISTEN_OPTS_INIT;
 	int fd;
 
-	fd = unix_stream_listen(socket_path);
+	fd = unix_stream_listen(socket_path, &opts);
 	if (fd < 0)
 		die_errno("unable to bind to '%s'", socket_path);