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+ -->
6 <refentry id=
"sd_event_get_fd" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
9 <title>sd_event_get_fd
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>sd_event_get_fd
</refentrytitle>
15 <manvolnum>3</manvolnum>
19 <refname>sd_event_get_fd
</refname>
21 <refpurpose>Obtain a file descriptor to poll for event loop events
</refpurpose>
26 <funcsynopsisinfo>#include
<systemd/sd-event.h
></funcsynopsisinfo>
29 <funcdef>int
<function>sd_event_get_fd
</function></funcdef>
30 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
37 <title>Description
</title>
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
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>
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
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>
59 <title>Return Value
</title>
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>
67 <para>Returned errors may indicate the following problems:
</para>
71 <term><constant>-EINVAL
</constant></term>
73 <listitem><para><parameter>event
</parameter> is not a valid pointer to an
74 <structname>sd_event
</structname> structure.
</para></listitem>
78 <term><constant>-ECHILD
</constant></term>
80 <listitem><para>The event loop has been created in a different process.
</para></listitem>
88 <title>Examples
</title>
91 <title>Integration in the GLib event loop
</title>
93 <programlisting><xi:include href=
"glib-event-glue.c" parse=
"text" /></programlisting>
97 <xi:include href=
"libsystemd-pkgconfig.xml" />
100 <title>See Also
</title>
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>