sd_event_get_fd(3) — Linux manual page

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

SD_EVENT_GET_FD(3)             sd_event_get_fd            SD_EVENT_GET_FD(3)

NAME         top

       sd_event_get_fd - Obtain a file descriptor to poll for event loop
       events

SYNOPSIS         top

       #include <systemd/sd-event.h>

       int sd_event_get_fd(sd_event *event);

DESCRIPTION         top

       sd_event_get_fd() returns the file descriptor that an event loop
       object returned by the sd_event_new(3) function uses to wait for
       events. This file descriptor may itself be polled for POLLIN/EPOLLIN
       events. This makes it possible to embed an sd-event(3) event loop
       into another, possibly foreign, event loop.

       The returned file descriptor refers to an epoll(7) object. It is
       recommended not to alter it by invoking epoll_ctl(2) on it, in order
       to avoid interference with the event loop's inner logic and
       assumptions.

RETURN VALUE         top

       On success, sd_event_get_fd() returns a non-negative file descriptor.
       On failure, it returns a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           event is not a valid pointer to an sd_event structure.

       -ECHILD
           The event loop has been created in a different process.

EXAMPLES         top

       Example 1. Integration in the GLib event loop

           /* SPDX-License-Identifier: MIT */

           #include <stdlib.h>
           #include <glib.h>
           #include <systemd/sd-event.h>

           typedef struct SDEventSource {
             GSource source;
             GPollFD pollfd;
             sd_event *event;
           } SDEventSource;

           static gboolean event_prepare(GSource *source, gint *timeout_) {
             return sd_event_prepare(((SDEventSource *)source)->event) > 0;
           }

           static gboolean event_check(GSource *source) {
             return sd_event_wait(((SDEventSource *)source)->event, 0) > 0;
           }

           static gboolean event_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) {
             return sd_event_dispatch(((SDEventSource *)source)->event) > 0;
           }

           static void event_finalize(GSource *source) {
             sd_event_unref(((SDEventSource *)source)->event);
           }

           static GSourceFuncs event_funcs = {
             .prepare = event_prepare,
             .check = event_check,
             .dispatch = event_dispatch,
             .finalize = event_finalize,
           };

           GSource *g_sd_event_create_source(sd_event *event) {
             SDEventSource *source;

             source = (SDEventSource *)g_source_new(&event_funcs, sizeof(SDEventSource));

             source->event = sd_event_ref(event);
             source->pollfd.fd = sd_event_get_fd(event);
             source->pollfd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;

             g_source_add_poll((GSource *)source, &source->pollfd);

             return (GSource *)source;
           }

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

       sd-event(3), sd_event_new(3), sd_event_wait(3), epoll_ctl(2),
       epoll(7)

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 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-11.)  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 246                                               SD_EVENT_GET_FD(3)

Pages that refer to this page: sd-event(3)sd_event_armed(3)SD_EVENT_ARMED(3)sd_event_dispatch(3)sd_event_exiting(3)SD_EVENT_EXITING(3)sd_event_finished(3)SD_EVENT_FINISHED(3)sd_event_get_iteration(3)sd_event_get_state(3)sd_event_initial(3)SD_EVENT_INITIAL(3)sd_event_loop(3)sd_event_pending(3)SD_EVENT_PENDING(3)sd_event_prepare(3)sd_event_preparing(3)SD_EVENT_PREPARING(3)sd_event_run(3)sd_event_running(3)SD_EVENT_RUNNING(3)sd_event_wait(3)30-systemd-environment-d-generator(7)systemd.directives(7)systemd.index(7)