man/sd_event_get_fd.xml

   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, library or module instance.</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>History</title>
 101     <para><function>sd_event_get_fd()</function> was added in version 217.</para>
 102   </refsect1>
 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>2</manvolnum></citerefentry>,
 112       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 113     </para>
 114   </refsect1>
 115
 116 </refentry>