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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>