sd_event_get_fd

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## Name

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

## Synopsis

    #include <systemd/sd-bus.h>

`int sd_event_get_fd(` | sd_bus *event`)`;

## Description

`sd_event_get_fd()` returns the file descriptor that the event loop object returned by the sd_event_new(3) function uses to wait for events. This file descriptor can be polled for events. This makes it possible to embed the sd-event(3) event loop inside of another event loop.

## Return Value

On success, `sd_event_get_fd()` returns a non-negative integer. 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 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

`sd_event_get_fd()` is available 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_ref(3)