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<refentry id="sd_event_add_child" conditional="ENABLE_KDBUS">

<refentryinfo>

<title>sd_event_add_child</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>More text</contrib>

<firstname>Zbigniew</firstname>

<surname>Jędrzejewski-Szmek</surname>

<email>zbyszek@in.waw.pl</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_event_add_child</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_event_add_child</refname>

<refname>sd_event_source_get_child_pid</refname>

<refpurpose>Add a child state change event source to an event loop</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int <function>sd_event_add_child</function></funcdef>

<paramdef>sd_event *<parameter>event</parameter></paramdef>

<paramdef>sd_event_source **<parameter>source</parameter></paramdef>

<paramdef>pid_t <parameter>pid</parameter></paramdef>

<paramdef>int <parameter>options</parameter></paramdef>

<paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>

<paramdef>void *<parameter>userdata</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef>

<paramdef>sd_event_source *<parameter>s</parameter></paramdef>

<paramdef>const siginfo_t *<parameter>si</parameter></paramdef>

<paramdef>void *<parameter>userdata</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>

<paramdef>sd_event_source *<parameter>source</parameter></paramdef>

<paramdef>pid_t *<parameter>pid</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_event_add_child()</function> adds a new child

state change event source to an event loop object. The event loop

is specified in <parameter>event</parameter>, the event source is

returned in the <parameter>source</parameter> parameter. The

<parameter>pid</parameter> parameter specifies the process to

watch. The <parameter>handler</parameter> must reference a

function to call when the process changes state. The handler

function will be passed the <parameter>userdata</parameter>

pointer, which may be chosen freely by the caller. The handler

also receives a pointer to a <structname>const

siginfo_t</structname> structure containing the information about

the event. The <parameter>options</parameter> parameter determines

which state changes will be watched for. It must contain an OR-ed

mask of <constant>WEXITED</constant> (watch for the child

terminating), <constant>WSTOPPED</constant> (watch for the child

being stopped by a signal), and <constant>WCONTINUED</constant>

(watch for the child being resumed by a signal). See

<citerefentry><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>

for further information.</para>

<para>Only a single handler may be installed for a specific

child. The handler is enabled

for a single event (<constant>SD_EVENT_ONESHOT</constant>),

but this may be

changed with

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.

If the handler function returns a negative error code, it will be

disabled after the invocation, even if

<constant>SD_EVENT_ON</constant> mode is set.

</para>

<para><function>sd_event_source_get_child_pid()</function>

retrieves the configured <parameter>pid</parameter> of a child

state change event source created previously with

<function>sd_event_add_child()</function>. It takes the event

source object as the <parameter>source</parameter> parameter and a

pointer to <type>pid_t</type> to return the result in.

</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, these functions return 0 or a positive

integer. On failure, they return a negative errno-style error

code.</para>

</refsect1>

<refsect1>

<title>Errors</title>

<para>Returned errors may indicate the following problems:</para>

<variablelist>

<varlistentry>

<term><constant>-ENOMEM</constant></term>

<listitem><para>Not enough memory to allocate an object.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EINVAL</constant></term>

<listitem><para>An invalid argument has been passed. This includes

specyfing an empty mask in <parameter>options</parameter> or a mask

which contains values different than a combination of

<constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and

<constant>WCONTINUED</constant>.

</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EBUSY</constant></term>

<listitem><para>An handler is already installed for this

child.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ESTALE</constant></term>

<listitem><para>The event loop is already terminated.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ECHILD</constant></term>

<listitem><para>The event loop has been created in a different process.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Notes</title>

<para><function>sd_event_add_child()</function> and the other functions

described here are available as a shared library, which can be

compiled and linked to with the

<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</para>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>