On Wed, Dec 31, 2025 at 05:41:34PM +0000, Paul Tarjan via GitGitGadget wrote:

From: Paul Tarjan <redacted>

Implement fsmonitor for Linux using the inotify API, bringing it to
feature parity with existing Windows and macOS implementations.

The Linux implementation uses inotify to monitor filesystem events.
Unlike macOS's FSEvents which can watch a single root directory,
inotify requires registering watches on every directory of interest.
The implementation carefully handles directory renames and moves
using inotify's cookie mechanism to track IN_MOVED_FROM/IN_MOVED_TO
event pairs.

Key implementation details:
- Uses inotify_init1(O_NONBLOCK) for non-blocking event monitoring
- Maintains bidirectional hashmaps between watch descriptors and paths
  for efficient event processing
- Handles directory creation, deletion, and renames dynamically
- Detects remote filesystems (NFS, CIFS, SMB, etc.) via statfs()
- Falls back to $HOME/.git-fsmonitor-* for socket when .git is remote
- Creates batches lazily (only for actual file events, not cookies)
  to avoid spurious sequence number increments

Build configuration:
- Enabled via FSMONITOR_DAEMON_BACKEND=linux and FSMONITOR_OS_SETTINGS=linux
- Requires NO_PTHREADS and NO_UNIX_SOCKETS to be unset
- Adds HAVE_LINUX_MAGIC_H for filesystem type detection

This would also need the below patch to support Meson. Would be great if
you include it, otherwise I can send it as a separate patch once this
topic lands. Thanks!

Patrick

-- >8 --

diff --git a/meson.build b/meson.build
index dd52efd1c8..0130d40702 100644
--- a/meson.build
+++ b/meson.build

@@ -1322,6 +1322,9 @@ endif
 fsmonitor_backend = ''
 if host_machine.system() == 'windows'
   fsmonitor_backend = 'win32'
+elif host_machine.system() == 'linux' and threads.found() and compiler.has_header('linux/magic.h')
+  fsmonitor_backend = 'linux'
+  libgit_c_args += '-DHAVE_LINUX_MAGIC_H'
 elif host_machine.system() == 'darwin'
   fsmonitor_backend = 'darwin'
   libgit_dependencies += dependency('CoreServices')