1<?xml version='1.0'?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
7
8  <refentryinfo>
9    <title>sd_event_get_fd</title>
10    <productname>systemd</productname>
11  </refentryinfo>
12
13  <refmeta>
14    <refentrytitle>sd_event_get_fd</refentrytitle>
15    <manvolnum>3</manvolnum>
16  </refmeta>
17
18  <refnamediv>
19    <refname>sd_event_get_fd</refname>
20
21    <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
22  </refnamediv>
23
24  <refsynopsisdiv>
25    <funcsynopsis>
26      <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
27
28      <funcprototype>
29        <funcdef>int <function>sd_event_get_fd</function></funcdef>
30        <paramdef>sd_event *<parameter>event</parameter></paramdef>
31      </funcprototype>
32
33    </funcsynopsis>
34  </refsynopsisdiv>
35
36  <refsect1>
37    <title>Description</title>
38
39    <para><function>sd_event_get_fd()</function> returns the file
40    descriptor that an event loop object returned by the
41    <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
42    function uses to wait for events. This file descriptor may itself
43    be polled for
44    <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
45    events. This makes it possible to embed an
46    <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
47    event loop into another, possibly foreign, event loop.</para>
48
49    <para>The returned file descriptor refers to an <citerefentry
50    project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
51    object. It is recommended not to alter it by invoking
52    <citerefentry
53    project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
54    on it, in order to avoid interference with the event loop's inner
55    logic and assumptions.</para>
56  </refsect1>
57
58  <refsect1>
59    <title>Return Value</title>
60
61    <para>On success, <function>sd_event_get_fd()</function> returns a non-negative file descriptor. On
62    failure, it returns a negative errno-style error code.</para>
63
64    <refsect2>
65      <title>Errors</title>
66
67      <para>Returned errors may indicate the following problems:</para>
68
69      <variablelist>
70        <varlistentry>
71          <term><constant>-EINVAL</constant></term>
72
73          <listitem><para><parameter>event</parameter> is not a valid pointer to an
74          <structname>sd_event</structname> structure.</para></listitem>
75        </varlistentry>
76
77        <varlistentry>
78          <term><constant>-ECHILD</constant></term>
79
80          <listitem><para>The event loop has been created in a different process.</para></listitem>
81
82        </varlistentry>
83      </variablelist>
84    </refsect2>
85  </refsect1>
86
87  <refsect1>
88    <title>Examples</title>
89
90    <example>
91      <title>Integration in the GLib event loop</title>
92
93      <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
94    </example>
95  </refsect1>
96
97  <xi:include href="libsystemd-pkgconfig.xml" />
98
99  <refsect1>
100    <title>See Also</title>
101
102    <para>
103      <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
104      <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
105      <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
106      <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
107      <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
108    </para>
109  </refsect1>
110
111</refentry>
112