Description¶

sd_event_add_inotify() adds a new inotify(7) file system inode event source to an event loop. The event loop object is specified in the event parameter, the event source object is returned in the source parameter. The path parameter specifies the path of the file system inode to watch. The mask parameter specifies which types of inode events to watch specifically. It must contain an OR-ed combination of IN_ACCESS, IN_ATTRIB, IN_CLOSE_WRITE, … flags. See inotify(7) for further information.

The handler must reference a function to call when the inode changes or NULL. The handler function will be passed the userdata pointer, which may be chosen freely by the caller. The handler also receives a pointer to a struct inotify_event structure containing information about the inode event. The handler may return negative to signal an error (see below), other return values are ignored. If handler is NULL, a default handler that calls sd_event_exit(3) will be used.

sd_event_add_inotify_fd() is identical to sd_event_add_inotify(), except that it takes a file descriptor to an inode (possibly an O_PATH one, but any other will do too) instead of a path in the file system.

If multiple event sources are installed for the same inode the backing inotify watch descriptor is automatically shared. The mask parameter may contain any flag defined by the inotify API, with the exception of IN_MASK_ADD.

The handler is enabled continuously (SD_EVENT_ON), but this may be changed with sd_event_source_set_enabled(3). Alternatively, the IN_ONESHOT mask flag may be used to request SD_EVENT_ONESHOT mode. If the handler function returns a negative error code, it will be disabled after the invocation, even if the SD_EVENT_ON mode was requested before.

As a special limitation the priority of inotify event sources may only be altered (see sd_event_source_set_priority(3)) in the time between creation of the event source object with sd_event_add_inotify() and the beginning of the next event loop iteration. Attempts of changing the priority any later will be refused. Consider freeing and allocating a new inotify event source to change the priority at that point.

To destroy an event source object use sd_event_source_unref(3), but note that the event source is only removed from the event loop when all references to the event source are dropped. To make sure an event source does not fire anymore, even when there's still a reference to it kept, consider disabling it with sd_event_source_set_enabled(3).

If the second parameter of sd_event_add_inotify() is passed as NULL no reference to the event source object is returned. In this case the event source is considered "floating", and will be destroyed implicitly when the event loop itself is destroyed.

If the handler parameter to sd_event_add_inotify() is NULL, and the event source fires, this will be considered a request to exit the event loop. In this case, the userdata parameter, cast to an integer, is passed as the exit code parameter to sd_event_exit(3).

sd_event_source_get_inotify_mask() retrieves the configured inotify watch mask of an event source created previously with sd_event_add_inotify(). It takes the event source object as the source parameter and a pointer to a uint32_t variable to return the mask in.

Return Value¶

On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.

Examples¶

/* SPDX-License-Identifier: MIT-0 */

#include <stdio.h>
#include <string.h>
#include <sys/inotify.h>

#include <systemd/sd-event.h>

#define _cleanup_(f) __attribute__((cleanup(f)))

static int inotify_handler(sd_event_source *source,
                           const struct inotify_event *event,
                           void *userdata) {

  const char *desc = NULL;

  sd_event_source_get_description(source, &desc);

  if (event->mask & IN_Q_OVERFLOW)
    printf("inotify-handler <%s>: overflow\n", desc);
  else if (event->mask & IN_CREATE)
    printf("inotify-handler <%s>: create on %s\n", desc, event->name);
  else if (event->mask & IN_DELETE)
    printf("inotify-handler <%s>: delete on %s\n", desc, event->name);
  else if (event->mask & IN_MOVED_TO)
    printf("inotify-handler <%s>: moved-to on %s\n", desc, event->name);

  /* Terminate the program if an "exit" file appears */
  if ((event->mask & (IN_CREATE|IN_MOVED_TO)) &&
      strcmp(event->name, "exit") == 0)
    sd_event_exit(sd_event_source_get_event(source), 0);

  return 1;
}

int main(int argc, char **argv) {
  _cleanup_(sd_event_unrefp) sd_event *event = NULL;
  _cleanup_(sd_event_source_unrefp) sd_event_source *source1 = NULL, *source2 = NULL;

  const char *path1 = argc > 1 ? argv[1] : "/tmp";
  const char *path2 = argc > 2 ? argv[2] : NULL;

  /* Note: failure handling is omitted for brevity */

  sd_event_default(&event);

  sd_event_add_inotify(event, &source1, path1,
                       IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
                       inotify_handler, NULL);
  if (path2)
    sd_event_add_inotify(event, &source2, path2,
                         IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
                         inotify_handler, NULL);

  sd_event_loop(event);

  return 0;
}

Notes¶

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.

History¶

sd_event_inotify_handler_t(), sd_event_add_inotify(), and sd_event_source_get_inotify_mask() were added in version 239.

sd_event_add_inotify_fd() was added in version 250.

See Also¶

systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_defer(3), sd_event_add_child(3), sd_event_source_set_enabled(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_set_description(3), sd_event_source_set_floating(3), waitid(2)