man/sd_event_get_fd.xml

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   8   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  23
  24 <refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_get_fd</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>More text</contrib>
  33         <firstname>Zbigniew</firstname>
  34         <surname>Jędrzejewski-Szmek</surname>
  35         <email>zbyszek@in.waw.pl</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_get_fd</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_get_fd</refname>
  47
  48     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  49   </refnamediv>
  50
  51   <refsynopsisdiv>
  52     <funcsynopsis>
  53       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  54
  55       <funcprototype>
  56         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  57         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  58       </funcprototype>
  59
  60     </funcsynopsis>
  61   </refsynopsisdiv>
  62
  63   <refsect1>
  64     <title>Description</title>
  65
  66     <para><function>sd_event_get_fd()</function> returns the file
  67     descriptor that an event loop object returned by the
  68     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  69     function uses to wait for events. This file descriptor may itself
  70     be polled for
  71     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  72     events. This makes it possible to embed an
  73     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  74     event loop into another, possibly foreign, event loop.</para>
  75
  76     <para>The returned file descriptor refers to an <citerefentry
  77     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  78     object. It is recommended not to alter it by invoking
  79     <citerefentry
  80     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  81     on it, in order to avoid interference with the event loop's inner
  82     logic and assumptions.</para>
  83   </refsect1>
  84
  85   <refsect1>
  86     <title>Return Value</title>
  87
  88     <para>On success, <function>sd_event_get_fd()</function> returns a
  89     non-negative file descriptor. On failure, it returns a negative
  90     errno-style error code.</para>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>Errors</title>
  95
  96     <para>Returned errors may indicate the following problems:</para>
  97
  98     <variablelist>
  99       <varlistentry>
 100         <term><constant>-EINVAL</constant></term>
 101
 102         <listitem><para><parameter>event</parameter> is not a valid
 103         pointer to an <structname>sd_event</structname> structure.
 104         </para></listitem>
 105       </varlistentry>
 106
 107       <varlistentry>
 108         <term><constant>-ECHILD</constant></term>
 109
 110         <listitem><para>The event loop has been created in a different process.</para></listitem>
 111
 112       </varlistentry>
 113     </variablelist>
 114   </refsect1>
 115
 116   <refsect1>
 117     <title>Examples</title>
 118
 119     <example>
 120       <title>Integration in the GLib event loop</title>
 121
 122       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
 123     </example>
 124   </refsect1>
 125
 126   <xi:include href="libsystemd-pkgconfig.xml" />
 127
 128   <refsect1>
 129     <title>See Also</title>
 130
 131     <para>
 132       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 133       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 134       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 135       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 136       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 137     </para>
 138   </refsect1>
 139
 140 </refentry>