[PATCH v10 00/12] fsmonitor: implement filesystem change listener for Linux
STALE169d
From: Paul Tarjan via GitGitGadget <hidden>
Date: 2026-03-05 01:16:22
Revision v10 of 10 in this series.
Revisions (10)
This series implements the built-in fsmonitor daemon for Linux using the inotify API, bringing it to feature parity with the existing Windows and macOS implementations. It also fixes two memory leaks in the platform-independent daemon code and deduplicates the IPC and settings logic that is now shared between macOS and Linux. 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 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 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. This series builds on work from https://github.com/git/git/pull/1352 by Eric DeCosta and https://github.com/git/git/pull/1667 by Marziyeh Esipreh, updated to work with the current codebase and address all review feedback. Changes since v8: * Replaced close_fd_above_stderr flag with generic pre_exec_cb callback in struct child_process per Junio's review * Provided close_fd_above_stderr() as a ready-made callback function * Fixed Windows build: close_fd_above_stderr() compiles as a no-op on Windows since there is no fork/exec Changes since v7: * Added patch 12: convert khash to strset in do_handle_client (Patrick's #leftoverbit suggestion) * Fixed "Forcing shutdown" trace message to start with lowercase * Fixed redundant statfs() call in find_mount() (caller already had the result) * Fixed CMakeLists.txt GIT-BUILD-OPTIONS: was hardcoded to "win32" for FSMONITOR_DAEMON_BACKEND and FSMONITOR_OS_SETTINGS, now uses the CMake variables * Fixed uninitialized strset on trivial response path (STRSET_INIT) * Removed V9FS_MAGIC from get_fs_typename() to match is_remote_fs() (9p is local VM mounts) * Split 30-second stop timeout into its own commit per review request * Fixed misleading indentation on shutdown assignment in handle_events() * Updated commit messages to describe all changes (test hardening, fsmonitor-ipc.c spawn changes) * Updated Makefile comment for FSMONITOR_OS_SETTINGS to mention fsm-ipc Changes since v6: * Introduced FSMONITOR_OS_SETTINGS build variable (set to "unix" for macOS and Linux, "win32" for Windows) to eliminate if/else conditionals in Makefile, meson.build, and CMakeLists.txt per Junio's review * Moved fsm-path-utils from FSMONITOR_OS_SETTINGS to FSMONITOR_DAEMON_BACKEND since path-utils files are platform-specific * Removed V9FS_MAGIC from remote filesystem detection (9p is used for local VM/container host mounts where fsmonitor works fine) * Removed redundant #include <libgen.h> (already provided by compat/posix.h) * Fixed cookie wait comment wording ("see" to "observe") * Rewrote commit messages for IPC and settings dedup patches Changes since v5: * Split monolithic commit into 10-patch series per Patrick's review * Deduplicated fsm-ipc and fsm-settings into shared Unix implementations * Rewrote commit message with prose paragraphs, explain inotify vs fanotify, removed "Issues addressed" sections, added Based-on-patch-by trailers * Removed redundant includes already provided by compat/posix.h * Fixed error/trace message capitalization per coding guidelines * Fixed stale rename check interval from 1000 seconds to 1 second * Changed poll timeout from 1ms to 50ms to reduce idle CPU wake-ups * Replaced infinite pthread_cond_wait cookie loop with one-second pthread_cond_timedwait (prevents daemon hangs on overlay filesystems where events are never delivered) * Added pthread_cond_timedwait to Windows pthread compatibility layer * Separated test into its own commit with smoke test that skips when inotify events are not delivered (e.g., overlayfs with older kernels) * Fixed test hang on Fedora CI: stop_git() looped forever when ps was unavailable because bash in POSIX/sh mode returns exit 0 from kill with an empty process group argument. Fixed by falling back to /proc/$pid/stat for process group ID and guarding stop_git against empty pgid. * Redirect spawn_daemon() stdout/stderr to /dev/null and close inherited file descriptors to prevent the intermediate process from holding test pipe file descriptors * Call setsid() on daemon detach to prevent shells with job control from waiting on the daemon process group * Close inherited file descriptors 3-7 in the test watchdog subprocess * Added 30-second timeout to "fsmonitor--daemon stop" to prevent indefinite blocking * Added helpful error message when inotify watch limit (max_user_watches) is reached * Initialize fd_inotify to -1 and use fd >= 0 check for correct fd 0 handling * Use sysconf(_SC_OPEN_MAX) instead of hardcoded 1024 for fd close limit * Check setsid() return value Changes since v4: * Added Meson build support Changes since v3: * Fix crash on rapid nested directory creation (EEXIST from inotify_add_watch with IN_MASK_CREATE) * Extensive stress testing Changes since v2: * Fix khash memory leak in do_handle_client Changes since v1: * Fix hashmap memory leak in fsmonitor_run_daemon() Paul Tarjan (12): fsmonitor: fix khash memory leak in do_handle_client fsmonitor: fix hashmap memory leak in fsmonitor_run_daemon compat/win32: add pthread_cond_timedwait fsmonitor: use pthread_cond_timedwait for cookie wait fsmonitor: rename fsm-ipc-darwin.c to fsm-ipc-unix.c fsmonitor: rename fsm-settings-darwin.c to fsm-settings-unix.c fsmonitor: implement filesystem change listener for Linux run-command: add pre-exec callback for child processes fsmonitor: close inherited file descriptors and detach in daemon fsmonitor: add timeout to daemon stop command fsmonitor: add tests for Linux fsmonitor: convert shown khash to strset in do_handle_client Documentation/config/fsmonitor--daemon.adoc | 4 +- Documentation/git-fsmonitor--daemon.adoc | 28 +- Makefile | 6 +- builtin/fsmonitor--daemon.c | 92 ++- compat/fsmonitor/fsm-health-linux.c | 33 + .../{fsm-ipc-darwin.c => fsm-ipc-unix.c} | 0 compat/fsmonitor/fsm-listen-linux.c | 746 ++++++++++++++++++ compat/fsmonitor/fsm-path-utils-linux.c | 217 +++++ ...-settings-darwin.c => fsm-settings-unix.c} | 0 compat/win32/pthread.c | 26 + compat/win32/pthread.h | 2 + config.mak.uname | 12 +- contrib/buildsystems/CMakeLists.txt | 33 +- fsmonitor-ipc.c | 3 + meson.build | 13 +- run-command.c | 18 + run-command.h | 16 + t/t7527-builtin-fsmonitor.sh | 89 ++- 18 files changed, 1275 insertions(+), 63 deletions(-) create mode 100644 compat/fsmonitor/fsm-health-linux.c rename compat/fsmonitor/{fsm-ipc-darwin.c => fsm-ipc-unix.c} (100%) create mode 100644 compat/fsmonitor/fsm-listen-linux.c create mode 100644 compat/fsmonitor/fsm-path-utils-linux.c rename compat/fsmonitor/{fsm-settings-darwin.c => fsm-settings-unix.c} (100%) base-commit: 3e0db84c88c57e70ac8be8c196dfa92c5d656fbc Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2147%2Fptarjan%2Fclaude%2Fupdate-pr-1352-current-85Gk8-v10 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2147/ptarjan/claude/update-pr-1352-current-85Gk8-v10 Pull-Request: https://github.com/git/git/pull/2147 Range-diff vs v9: 1: 4d4dec8fa1 = 1: 4d4dec8fa1 fsmonitor: fix khash memory leak in do_handle_client 2: cb270120f0 = 2: cb270120f0 fsmonitor: fix hashmap memory leak in fsmonitor_run_daemon 3: 44a063074d = 3: 44a063074d compat/win32: add pthread_cond_timedwait 4: b1081d1e13 = 4: b1081d1e13 fsmonitor: use pthread_cond_timedwait for cookie wait 5: dec0fb144f = 5: dec0fb144f fsmonitor: rename fsm-ipc-darwin.c to fsm-ipc-unix.c 6: b2aaadb4ae = 6: b2aaadb4ae fsmonitor: rename fsm-settings-darwin.c to fsm-settings-unix.c 7: 03cf12d01b = 7: 03cf12d01b fsmonitor: implement filesystem change listener for Linux 8: 31fa1fb324 ! 8: 39dcfbb7c8 run-command: add pre-exec callback for child processes @@ Commit message Signed-off-by: Paul Tarjan [off-list ref] ## run-command.c ## -@@ run-command.c: static void trace_run_command(const struct child_process *cp) - strbuf_release(&buf); +@@ run-command.c: static void atfork_parent(struct atfork_state *as) + "restoring signal mask"); + #endif } ++ + #endif /* GIT_WINDOWS_NATIVE */ +void close_fd_above_stderr(void) +{ ++#ifndef GIT_WINDOWS_NATIVE + long max_fd = sysconf(_SC_OPEN_MAX); + int fd; + if (max_fd < 0 || max_fd > 4096) @@ run-command.c: static void trace_run_command(const struct child_process *cp) + if (fd != child_notifier) + close(fd); + } ++#endif +} + - int start_command(struct child_process *cmd) + static inline void set_cloexec(int fd) { - int need_in, need_out, need_err; + int flags = fcntl(fd, F_GETFD); @@ run-command.c: fail_pipe: child_close(cmd->out); } @@ run-command.h: struct child_process { +/** + * Close file descriptors 3 and above. Suitable for use as a + * pre_exec_cb to prevent the child from inheriting pipe endpoints -+ * or other descriptors from the parent environment. ++ * or other descriptors from the parent environment. On Windows ++ * this is a no-op since there is no fork/exec. + */ +void close_fd_above_stderr(void); + 9: c963074cbd = 9: 5db0591c15 fsmonitor: close inherited file descriptors and detach in daemon 10: ee3ee75c94 = 10: 8a9a6ba4fa fsmonitor: add timeout to daemon stop command 11: 54bd8f604a = 11: 27d5560007 fsmonitor: add tests for Linux 12: e603fc7dde = 12: 8ea20aab4c fsmonitor: convert shown khash to strset in do_handle_client -- gitgitgadget