man/sd_event_get_fd.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   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   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_event_get_fd</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_event_get_fd</refname>
  23
  24     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <funcsynopsis>
  29       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  30
  31       <funcprototype>
  32         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  33         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  34       </funcprototype>
  35
  36     </funcsynopsis>
  37   </refsynopsisdiv>
  38
  39   <refsect1>
  40     <title>Description</title>
  41
  42     <para><function>sd_event_get_fd()</function> returns the file
  43     descriptor that an event loop object returned by the
  44     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  45     function uses to wait for events. This file descriptor may itself
  46     be polled for
  47     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  48     events. This makes it possible to embed an
  49     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  50     event loop into another, possibly foreign, event loop.</para>
  51
  52     <para>The returned file descriptor refers to an <citerefentry
  53     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  54     object. It is recommended not to alter it by invoking
  55     <citerefentry
  56     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  57     on it, in order to avoid interference with the event loop's inner
  58     logic and assumptions.</para>
  59   </refsect1>
  60
  61   <refsect1>
  62     <title>Return Value</title>
  63
  64     <para>On success, <function>sd_event_get_fd()</function> returns a
  65     non-negative file descriptor. On failure, it returns a negative
  66     errno-style error code.</para>
  67   </refsect1>
  68
  69   <refsect1>
  70     <title>Errors</title>
  71
  72     <para>Returned errors may indicate the following problems:</para>
  73
  74     <variablelist>
  75       <varlistentry>
  76         <term><constant>-EINVAL</constant></term>
  77
  78         <listitem><para><parameter>event</parameter> is not a valid
  79         pointer to an <structname>sd_event</structname> structure.
  80         </para></listitem>
  81       </varlistentry>
  82
  83       <varlistentry>
  84         <term><constant>-ECHILD</constant></term>
  85
  86         <listitem><para>The event loop has been created in a different process.</para></listitem>
  87
  88       </varlistentry>
  89     </variablelist>
  90   </refsect1>
  91
  92   <refsect1>
  93     <title>Examples</title>
  94
  95     <example>
  96       <title>Integration in the GLib event loop</title>
  97
  98       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
  99     </example>
 100   </refsect1>
 101
 102   <xi:include href="libsystemd-pkgconfig.xml" />
 103
 104   <refsect1>
 105     <title>See Also</title>
 106
 107     <para>
 108       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 109       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 110       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 111       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 112       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 113     </para>
 114   </refsect1>
 115
 116 </refentry>