sd_event_add_inotify(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLES | NOTES | SEE ALSO | COLOPHON

SD_EVENT_ADD_INOTIFY(3)   sd_event_add_inotify   SD_EVENT_ADD_INOTIFY(3)

NAME         top

       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         top

       #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         top

       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 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.

       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         top

       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         top

       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         top

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

SEE ALSO         top

       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)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-04-01.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-04-01.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 248                                      SD_EVENT_ADD_INOTIFY(3)

Pages that refer to this page: sd-event(3)sd_event_add_child(3)sd_event_add_defer(3)sd_event_add_io(3)sd_event_add_signal(3)sd_event_add_time(3)sd_event_exit(3)sd_event_new(3)sd_event_run(3)sd_event_set_watchdog(3)sd_event_source_get_event(3)sd_event_source_get_pending(3)sd_event_source_set_description(3)sd_event_source_set_destroy_callback(3)sd_event_source_set_enabled(3)sd_event_source_set_exit_on_failure(3)sd_event_source_set_floating(3)sd_event_source_set_prepare(3)sd_event_source_set_priority(3)sd_event_source_set_ratelimit(3)sd_event_source_set_userdata(3)sd_event_source_unref(3)sd_event_wait(3)systemd.directives(7)systemd.index(7)