NAME

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

SYNOPSIS

       #include <systemd/sd-event.h>

       int sd_event_get_fd(sd_event *event);

DESCRIPTION

       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

       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

       Example 1. Integration in the GLib event loop

           /***
             Copyright 2014 Tom Gundersen

             Permission is hereby granted, free of charge, to any person
             obtaining a copy of this software and associated documentation files
             (the "Software"), to deal in the Software without restriction,
             including without limitation the rights to use, copy, modify, merge,
             publish, distribute, sublicense, and/or sell copies of the Software,
             and to permit persons to whom the Software is furnished to do so,
             subject to the following conditions:

             The above copyright notice and this permission notice shall be
             included in all copies or substantial portions of the Software.

             THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
             EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
             MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
             NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
             BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
             ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
             CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
             SOFTWARE.
           ***/

           #include <stdlib.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

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

SEE ALSO

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