man/sd_event_add_child.xml

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   8   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  23
  24 <refentry id="sd_event_add_child">
  25
  26   <refentryinfo>
  27     <title>sd_event_add_child</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_add_child</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_add_child</refname>
  47     <refname>sd_event_source_get_child_pid</refname>
  48
  49     <refpurpose>Add a child state change event source to an event loop</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <funcsynopsis>
  54       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_event_add_child</function></funcdef>
  58         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  59         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  60         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  61         <paramdef>int <parameter>options</parameter></paramdef>
  62         <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>
  63         <paramdef>void *<parameter>userdata</parameter></paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef>
  68         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  69         <paramdef>const siginfo_t *<parameter>si</parameter></paramdef>
  70         <paramdef>void *<parameter>userdata</parameter></paramdef>
  71       </funcprototype>
  72
  73       <funcprototype>
  74         <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>
  75         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  76         <paramdef>pid_t *<parameter>pid</parameter></paramdef>
  77       </funcprototype>
  78
  79     </funcsynopsis>
  80   </refsynopsisdiv>
  81
  82   <refsect1>
  83     <title>Description</title>
  84
  85     <para><function>sd_event_add_child()</function> adds a new child
  86     state change event source to an event loop object. The event loop
  87     is specified in <parameter>event</parameter>, the event source is
  88     returned in the <parameter>source</parameter> parameter. The
  89     <parameter>pid</parameter> parameter specifies the process to
  90     watch. The <parameter>handler</parameter> must reference a
  91     function to call when the process changes state. The handler
  92     function will be passed the <parameter>userdata</parameter>
  93     pointer, which may be chosen freely by the caller. The handler
  94     also receives a pointer to a <structname>const
  95     siginfo_t</structname> structure containing the information about
  96     the event. The <parameter>options</parameter> parameter determines
  97     which state changes will be watched for. It must contain an OR-ed
  98     mask of <constant>WEXITED</constant> (watch for the child
  99     terminating), <constant>WSTOPPED</constant> (watch for the child
 100     being stopped by a signal), and <constant>WCONTINUED</constant>
 101     (watch for the child being resumed by a signal). See
 102     <citerefentry><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 103     for further information.</para>
 104
 105     <para>Only a single handler may be installed for a specific
 106     child. The handler is enabled
 107     for a single event (<constant>SD_EVENT_ONESHOT</constant>),
 108     but this may be
 109     changed with
 110     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 111     If the handler function returns a negative error code, it will be
 112     disabled after the invocation, even if
 113     <constant>SD_EVENT_ON</constant> mode is set.
 114     </para>
 115
 116     <para><function>sd_event_source_get_child_pid()</function>
 117     retrieves the configured <parameter>pid</parameter> of a child
 118     state change event source created previously with
 119     <function>sd_event_add_child()</function>. It takes the event
 120     source object as the <parameter>source</parameter> parameter and a
 121     pointer to <type>pid_t</type> to return the result in.
 122     </para>
 123   </refsect1>
 124
 125   <refsect1>
 126     <title>Return Value</title>
 127
 128     <para>On success, these functions return 0 or a positive
 129     integer. On failure, they return a negative errno-style error
 130     code.</para>
 131   </refsect1>
 132
 133   <refsect1>
 134     <title>Errors</title>
 135
 136     <para>Returned errors may indicate the following problems:</para>
 137
 138     <variablelist>
 139       <varlistentry>
 140         <term><constant>-ENOMEM</constant></term>
 141
 142         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 143       </varlistentry>
 144
 145       <varlistentry>
 146         <term><constant>-EINVAL</constant></term>
 147
 148         <listitem><para>An invalid argument has been passed. This includes
 149         specifying an empty mask in <parameter>options</parameter> or a mask
 150         which contains values different than a combination of
 151         <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
 152         <constant>WCONTINUED</constant>.
 153         </para></listitem>
 154
 155       </varlistentry>
 156
 157       <varlistentry>
 158         <term><constant>-EBUSY</constant></term>
 159
 160         <listitem><para>A handler is already installed for this
 161         child.</para></listitem>
 162
 163       </varlistentry>
 164
 165       <varlistentry>
 166         <term><constant>-ESTALE</constant></term>
 167
 168         <listitem><para>The event loop is already terminated.</para></listitem>
 169
 170       </varlistentry>
 171
 172       <varlistentry>
 173         <term><constant>-ECHILD</constant></term>
 174
 175         <listitem><para>The event loop has been created in a different process.</para></listitem>
 176
 177       </varlistentry>
 178
 179     </variablelist>
 180   </refsect1>
 181
 182   <refsect1>
 183     <title>Notes</title>
 184
 185     <para><function>sd_event_add_child()</function> and the other functions
 186     described here are available as a shared library, which can be
 187     compiled and linked to with the
 188     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 189     file.</para>
 190   </refsect1>
 191
 192   <refsect1>
 193     <title>See Also</title>
 194
 195     <para>
 196       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 197       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 198       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 199       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 200       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 201       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 202       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 203     </para>
 204   </refsect1>
 205
 206 </refentry>