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 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         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 2020-06-09.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-06-09.)  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 245                                          SD_EVENT_ADD_INOTIFY(3)

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