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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">

<refentryinfo>

<title>sd_event_get_fd</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>More text</contrib>

<firstname>Zbigniew</firstname>

<surname>Jędrzejewski-Szmek</surname>

<email>zbyszek@in.waw.pl</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_event_get_fd</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_event_get_fd</refname>

<refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int <function>sd_event_get_fd</function></funcdef>

<paramdef>sd_event *<parameter>event</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_event_get_fd()</function> returns the file

descriptor that an event loop object returned by the

<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>

function uses to wait for events. This file descriptor may itself

be polled for

<constant>POLLIN</constant>/<constant>EPOLLIN</constant>

events. This makes it possible to embed an

<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>

event loop into another, possibly foreign, event loop.</para>

<para>The returned file descriptor refers to an <citerefentry

project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>

object. It is recommended not to alter it by invoking

<citerefentry

project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>

on it, in order to avoid interference with the event loop's inner

logic and assumptions.</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, <function>sd_event_get_fd()</function> returns a

non-negative file descriptor. On failure, it returns a negative

errno-style error code.</para>

</refsect1>

<refsect1>

<title>Errors</title>

<para>Returned errors may indicate the following problems:</para>

<variablelist>

<varlistentry>

<term><constant>-EINVAL</constant></term>

<listitem><para><parameter>event</parameter> is not a valid

pointer to an <structname>sd_event</structname> structure.

</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ECHILD</constant></term>

<listitem><para>The event loop has been created in a different process.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Examples</title>

<example>

<title>Integration in the GLib event loop</title>

<programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>

</example>

</refsect1>

<xi:include href="libsystemd-pkgconfig.xml" />

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>