man/sd_event_get_fd.xml

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  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  25
  26 <refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
  27
  28   <refentryinfo>
  29     <title>sd_event_get_fd</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>More text</contrib>
  35         <firstname>Zbigniew</firstname>
  36         <surname>Jędrzejewski-Szmek</surname>
  37         <email>zbyszek@in.waw.pl</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_event_get_fd</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_event_get_fd</refname>
  49
  50     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <funcsynopsis>
  55       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  56
  57       <funcprototype>
  58         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  59         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  60       </funcprototype>
  61
  62     </funcsynopsis>
  63   </refsynopsisdiv>
  64
  65   <refsect1>
  66     <title>Description</title>
  67
  68     <para><function>sd_event_get_fd()</function> returns the file
  69     descriptor that an event loop object returned by the
  70     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  71     function uses to wait for events. This file descriptor may itself
  72     be polled for
  73     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  74     events. This makes it possible to embed an
  75     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  76     event loop into another, possibly foreign, event loop.</para>
  77
  78     <para>The returned file descriptor refers to an <citerefentry
  79     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  80     object. It is recommended not to alter it by invoking
  81     <citerefentry
  82     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  83     on it, in order to avoid interference with the event loop's inner
  84     logic and assumptions.</para>
  85   </refsect1>
  86
  87   <refsect1>
  88     <title>Return Value</title>
  89
  90     <para>On success, <function>sd_event_get_fd()</function> returns a
  91     non-negative file descriptor. On failure, it returns a negative
  92     errno-style error code.</para>
  93   </refsect1>
  94
  95   <refsect1>
  96     <title>Errors</title>
  97
  98     <para>Returned errors may indicate the following problems:</para>
  99
 100     <variablelist>
 101       <varlistentry>
 102         <term><constant>-EINVAL</constant></term>
 103
 104         <listitem><para><parameter>event</parameter> is not a valid
 105         pointer to an <structname>sd_event</structname> structure.
 106         </para></listitem>
 107       </varlistentry>
 108
 109       <varlistentry>
 110         <term><constant>-ECHILD</constant></term>
 111
 112         <listitem><para>The event loop has been created in a different process.</para></listitem>
 113
 114       </varlistentry>
 115     </variablelist>
 116   </refsect1>
 117
 118   <refsect1>
 119     <title>Examples</title>
 120
 121     <example>
 122       <title>Integration in the GLib event loop</title>
 123
 124       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
 125     </example>
 126   </refsect1>
 127
 128   <xi:include href="libsystemd-pkgconfig.xml" />
 129
 130   <refsect1>
 131     <title>See Also</title>
 132
 133     <para>
 134       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 135       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 136       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 139     </para>
 140   </refsect1>
 141
 142 </refentry>