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149c19ba1b
Implement the built-in fsmonitor daemon for Linux using the inotify API, bringing it to feature parity with the existing Windows and macOS implementations. The implementation uses inotify rather than fanotify because fanotify requires either CAP_SYS_ADMIN or CAP_PERFMON capabilities, making it unsuitable for an unprivileged user-space daemon. While inotify has the limitation of requiring a separate watch on every directory (unlike macOS's FSEvents, which can monitor an entire directory tree with a single watch), it operates without elevated privileges and provides the per-file event granularity needed for fsmonitor. The listener uses inotify_init1(O_NONBLOCK) with a poll loop that checks for events with a 50-millisecond timeout, keeping the inotify queue well-drained to minimize the risk of overflows. Bidirectional hashmaps map between watch descriptors and directory paths for efficient event resolution. Directory renames are tracked using inotify's cookie mechanism to correlate IN_MOVED_FROM and IN_MOVED_TO event pairs; a periodic check detects stale renames where the matching IN_MOVED_TO never arrived, forcing a resync. New directory creation triggers recursive watch registration to ensure all subdirectories are monitored. The IN_MASK_CREATE flag is used where available to prevent modifying existing watches, with a fallback for older kernels. When IN_MASK_CREATE is available and inotify_add_watch returns EEXIST, it means another thread or recursive scan has already registered the watch, so it is safe to ignore. Remote filesystem detection uses statfs() to identify network-mounted filesystems (NFS, CIFS, SMB, FUSE, etc.) via their magic numbers. Mount point information is read from /proc/mounts and matched against the statfs f_fsid to get accurate, human-readable filesystem type names for logging. When the .git directory is on a remote filesystem, the IPC socket falls back to $HOME or a user-configured directory via the fsmonitor.socketDir setting. Based-on-patch-by: Eric DeCosta <edecosta@mathworks.com> Based-on-patch-by: Marziyeh Esipreh <marziyeh.esipreh@gmail.com> Signed-off-by: Paul Tarjan <github@paulisageek.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
127 lines
4.1 KiB
Plaintext
127 lines
4.1 KiB
Plaintext
git-fsmonitor{litdd}daemon(1)
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=============================
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NAME
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----
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git-fsmonitor--daemon - A Built-in Filesystem Monitor
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SYNOPSIS
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--------
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[verse]
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'git fsmonitor{litdd}daemon' start
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'git fsmonitor{litdd}daemon' run
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'git fsmonitor{litdd}daemon' stop
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'git fsmonitor{litdd}daemon' status
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DESCRIPTION
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-----------
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A daemon to watch the working directory for file and directory
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changes using platform-specific filesystem notification facilities.
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This daemon communicates directly with commands like `git status`
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using the link:technical/api-simple-ipc.html[simple IPC] interface
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instead of the slower linkgit:githooks[5] interface.
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This daemon is built into Git so that no third-party tools are
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required.
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OPTIONS
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-------
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start::
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Starts a daemon in the background.
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run::
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Runs a daemon in the foreground.
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stop::
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Stops the daemon running in the current working
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directory, if present.
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status::
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Exits with zero status if a daemon is watching the
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current working directory.
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REMARKS
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-------
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This daemon is a long running process used to watch a single working
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directory and maintain a list of the recently changed files and
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directories. Performance of commands such as `git status` can be
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increased if they just ask for a summary of changes to the working
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directory and can avoid scanning the disk.
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When `core.fsmonitor` is set to `true` (see linkgit:git-config[1])
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commands, such as `git status`, will ask the daemon for changes and
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automatically start it (if necessary).
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For more information see the "File System Monitor" section in
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linkgit:git-update-index[1].
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CAVEATS
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-------
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The fsmonitor daemon does not currently know about submodules and does
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not know to filter out filesystem events that happen within a
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submodule. If fsmonitor daemon is watching a super repo and a file is
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modified within the working directory of a submodule, it will report
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the change (as happening against the super repo). However, the client
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will properly ignore these extra events, so performance may be affected
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but it will not cause an incorrect result.
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By default, the fsmonitor daemon refuses to work with network-mounted
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repositories; this may be overridden by setting `fsmonitor.allowRemote` to
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`true`. Note, however, that the fsmonitor daemon is not guaranteed to work
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correctly with all network-mounted repositories, so such use is considered
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experimental.
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On Mac OS and Linux, the inter-process communication (IPC) between various Git
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commands and the fsmonitor daemon is done via a Unix domain socket (UDS) -- a
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special type of file -- which is supported by native Mac OS and Linux filesystems,
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but not on network-mounted filesystems, NTFS, or FAT32. Other filesystems
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may or may not have the needed support; the fsmonitor daemon is not guaranteed
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to work with these filesystems and such use is considered experimental.
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By default, the socket is created in the `.git` directory. However, if the
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`.git` directory is on a network-mounted filesystem, it will instead be
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created at `$HOME/.git-fsmonitor-*` unless `$HOME` itself is on a
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network-mounted filesystem, in which case you must set the configuration
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variable `fsmonitor.socketDir` to the path of a directory on a native
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filesystem in which to create the socket file.
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If none of the above directories (`.git`, `$HOME`, or `fsmonitor.socketDir`)
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is on a native filesystem the fsmonitor daemon will report an
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error that will cause the daemon and the currently running command to exit.
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LINUX CAVEATS
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~~~~~~~~~~~~~
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On Linux, the fsmonitor daemon uses inotify to monitor filesystem events.
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The inotify system has per-user limits on the number of watches that can
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be created. The default limit is typically 8192 watches per user.
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For large repositories with many directories, you may need to increase
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this limit. Check the current limit with:
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cat /proc/sys/fs/inotify/max_user_watches
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To temporarily increase the limit:
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sudo sysctl fs.inotify.max_user_watches=65536
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To make the change permanent, add to `/etc/sysctl.conf`:
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fs.inotify.max_user_watches=65536
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CONFIGURATION
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-------------
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include::includes/cmd-config-section-all.adoc[]
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include::config/fsmonitor--daemon.adoc[]
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GIT
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---
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Part of the linkgit:git[1] suite
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