man/sd_event_add_child.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
   4 <!ENTITY % entities SYSTEM "custom-entities.ent" >
   5 %entities;
   6 ]>
   7
   8 <!--
   9   This file is part of systemd.
  10
  11   Copyright 2014 Zbigniew Jędrzejewski-Szmek
  12
  13   systemd is free software; you can redistribute it and/or modify it
  14   under the terms of the GNU Lesser General Public License as published by
  15   the Free Software Foundation; either version 2.1 of the License, or
  16   (at your option) any later version.
  17
  18   systemd is distributed in the hope that it will be useful, but
  19   WITHOUT ANY WARRANTY; without even the implied warranty of
  20   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  21   Lesser General Public License for more details.
  22
  23   You should have received a copy of the GNU Lesser General Public License
  24   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  25 -->
  26
  27 <refentry id="sd_event_add_child">
  28
  29   <refentryinfo>
  30     <title>sd_event_add_child</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>More text</contrib>
  36         <firstname>Zbigniew</firstname>
  37         <surname>Jędrzejewski-Szmek</surname>
  38         <email>zbyszek@in.waw.pl</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>sd_event_add_child</refentrytitle>
  45     <manvolnum>3</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>sd_event_add_child</refname>
  50     <refname>sd_event_source_get_child_pid</refname>
  51
  52     <refpurpose>Add a child state change event source to an event loop</refpurpose>
  53   </refnamediv>
  54
  55   <refsynopsisdiv>
  56     <funcsynopsis>
  57       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  58
  59       <funcprototype>
  60         <funcdef>int <function>sd_event_add_child</function></funcdef>
  61         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  62         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  63         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  64         <paramdef>int <parameter>options</parameter></paramdef>
  65         <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>
  66         <paramdef>void *<parameter>userdata</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef>
  71         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  72         <paramdef>const siginfo_t *<parameter>si</parameter></paramdef>
  73         <paramdef>void *<parameter>userdata</parameter></paramdef>
  74       </funcprototype>
  75
  76       <funcprototype>
  77         <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>
  78         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  79         <paramdef>pid_t *<parameter>pid</parameter></paramdef>
  80       </funcprototype>
  81
  82     </funcsynopsis>
  83   </refsynopsisdiv>
  84
  85   <refsect1>
  86     <title>Description</title>
  87
  88     <para><function>sd_event_add_child()</function> adds a new child
  89     state change event source to an event loop object. The event loop
  90     is specified in <parameter>event</parameter>, the event source is
  91     returned in the <parameter>source</parameter> parameter. The
  92     <parameter>pid</parameter> parameter specifies the process to
  93     watch. The <parameter>handler</parameter> must reference a
  94     function to call when the process changes state. The handler
  95     function will be passed the <parameter>userdata</parameter>
  96     pointer, which may be chosen freely by the caller. The handler
  97     also receives a pointer to a <structname>const
  98     siginfo_t</structname> structure containing the information about
  99     the event. The <parameter>options</parameter> parameter determines
 100     which state changes will be watched for. It must contain an OR-ed
 101     mask of <constant>WEXITED</constant> (watch for the child
 102     terminating), <constant>WSTOPPED</constant> (watch for the child
 103     being stopped by a signal), and <constant>WCONTINUED</constant>
 104     (watch for the child being resumed by a signal). See
 105     <citerefentry><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 106     for further information.</para>
 107
 108     <para>Only a single handler may be installed for a specific
 109     child. The handler is enabled
 110     for a single event (<constant>SD_EVENT_ONESHOT</constant>),
 111     but this may be
 112     changed with
 113     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 114     If the handler function returns a negative error code, it will be
 115     disabled after the invocation, even if
 116     <constant>SD_EVENT_ON</constant> mode is set.
 117     </para>
 118
 119     <para><function>sd_event_source_get_child_pid()</function>
 120     retrieves the configured <parameter>pid</parameter> of a child
 121     state change event source created previously with
 122     <function>sd_event_add_child()</function>. It takes the event
 123     source object as the <parameter>source</parameter> parameter and a
 124     pointer to <type>pid_t</type> to return the result in.
 125     </para>
 126   </refsect1>
 127
 128   <refsect1>
 129     <title>Return Value</title>
 130
 131     <para>On success, these functions return 0 or a positive
 132     integer. On failure, they return a negative errno-style error
 133     code.</para>
 134   </refsect1>
 135
 136   <refsect1>
 137     <title>Errors</title>
 138
 139     <para>Returned errors may indicate the following problems:</para>
 140
 141     <variablelist>
 142       <varlistentry>
 143         <term><constant>-ENOMEM</constant></term>
 144
 145         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 146       </varlistentry>
 147
 148       <varlistentry>
 149         <term><constant>-EINVAL</constant></term>
 150
 151         <listitem><para>An invalid argument has been passed. This includes
 152         specifying an empty mask in <parameter>options</parameter> or a mask
 153         which contains values different than a combination of
 154         <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
 155         <constant>WCONTINUED</constant>.
 156         </para></listitem>
 157
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term><constant>-EBUSY</constant></term>
 162
 163         <listitem><para>An handler is already installed for this
 164         child.</para></listitem>
 165
 166       </varlistentry>
 167
 168       <varlistentry>
 169         <term><constant>-ESTALE</constant></term>
 170
 171         <listitem><para>The event loop is already terminated.</para></listitem>
 172
 173       </varlistentry>
 174
 175       <varlistentry>
 176         <term><constant>-ECHILD</constant></term>
 177
 178         <listitem><para>The event loop has been created in a different process.</para></listitem>
 179
 180       </varlistentry>
 181
 182     </variablelist>
 183   </refsect1>
 184
 185   <refsect1>
 186     <title>Notes</title>
 187
 188     <para><function>sd_event_add_child()</function> and the other functions
 189     described here are available as a shared library, which can be
 190     compiled and linked to with the
 191     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 192     file.</para>
 193   </refsect1>
 194
 195   <refsect1>
 196     <title>See Also</title>
 197
 198     <para>
 199       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 200       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 201       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 202       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 203       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 204       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 205       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 206     </para>
 207   </refsect1>
 208
 209 </refentry>