man/sd_event_get_fd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_event_get_fd</title>
  13     <productname>systemd</productname>
  14
  15     <authorgroup>
  16       <author>
  17         <contrib>More text</contrib>
  18         <firstname>Zbigniew</firstname>
  19         <surname>Jędrzejewski-Szmek</surname>
  20         <email>zbyszek@in.waw.pl</email>
  21       </author>
  22     </authorgroup>
  23   </refentryinfo>
  24
  25   <refmeta>
  26     <refentrytitle>sd_event_get_fd</refentrytitle>
  27     <manvolnum>3</manvolnum>
  28   </refmeta>
  29
  30   <refnamediv>
  31     <refname>sd_event_get_fd</refname>
  32
  33     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  34   </refnamediv>
  35
  36   <refsynopsisdiv>
  37     <funcsynopsis>
  38       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  39
  40       <funcprototype>
  41         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  42         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  43       </funcprototype>
  44
  45     </funcsynopsis>
  46   </refsynopsisdiv>
  47
  48   <refsect1>
  49     <title>Description</title>
  50
  51     <para><function>sd_event_get_fd()</function> returns the file
  52     descriptor that an event loop object returned by the
  53     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  54     function uses to wait for events. This file descriptor may itself
  55     be polled for
  56     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  57     events. This makes it possible to embed an
  58     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  59     event loop into another, possibly foreign, event loop.</para>
  60
  61     <para>The returned file descriptor refers to an <citerefentry
  62     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  63     object. It is recommended not to alter it by invoking
  64     <citerefentry
  65     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  66     on it, in order to avoid interference with the event loop's inner
  67     logic and assumptions.</para>
  68   </refsect1>
  69
  70   <refsect1>
  71     <title>Return Value</title>
  72
  73     <para>On success, <function>sd_event_get_fd()</function> returns a
  74     non-negative file descriptor. On failure, it returns a negative
  75     errno-style error code.</para>
  76   </refsect1>
  77
  78   <refsect1>
  79     <title>Errors</title>
  80
  81     <para>Returned errors may indicate the following problems:</para>
  82
  83     <variablelist>
  84       <varlistentry>
  85         <term><constant>-EINVAL</constant></term>
  86
  87         <listitem><para><parameter>event</parameter> is not a valid
  88         pointer to an <structname>sd_event</structname> structure.
  89         </para></listitem>
  90       </varlistentry>
  91
  92       <varlistentry>
  93         <term><constant>-ECHILD</constant></term>
  94
  95         <listitem><para>The event loop has been created in a different process.</para></listitem>
  96
  97       </varlistentry>
  98     </variablelist>
  99   </refsect1>
 100
 101   <refsect1>
 102     <title>Examples</title>
 103
 104     <example>
 105       <title>Integration in the GLib event loop</title>
 106
 107       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
 108     </example>
 109   </refsect1>
 110
 111   <xi:include href="libsystemd-pkgconfig.xml" />
 112
 113   <refsect1>
 114     <title>See Also</title>
 115
 116     <para>
 117       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 118       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 119       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 120       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 121       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 122     </para>
 123   </refsect1>
 124
 125 </refentry>