Index · Directives systemd 239

Name

sd_event_add_inotify, sd_event_source_get_inotify_mask, sd_event_inotify_handler_t — Add an "inotify" file system inode event source to an event loop

Synopsis

#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_inotify_handler_t)(sd_event_source *s,
 const struct inotify_event *event,
 void *userdata);
 
int sd_event_add_inotify(sd_event *event,
 sd_event_source **source,
 const char *path,
 uint32_t mask,
 sd_event_inotify_handler_t handler,
 void *userdata);
 
int sd_event_source_get_inotify_mask(sd_event_source *source,
 uint32_t *mask);
 

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 handler must reference a function to call when the inode changes. 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 mask parameter specifie 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.

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.

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.

Errors

Returned errors may indicate the following problems:

-ENOMEM

Not enough memory to allocate an object.

-EINVAL

An invalid argument has been passed. This includes specifying a mask with IN_MASK_ADD set.

-ESTALE

The event loop is already terminated.

-ECHILD

The event loop has been created in a different process.

-EDOM

The passed event source is not an inotify process event source.

Examples

Example 1. A simple program that uses inotify to monitor one or two directories

#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

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

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), waitid(2)