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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2014 Zbigniew Jędrzejewski-Szmek
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<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 <systemd/sd-bus.h></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 futher 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><varname>-ENOMEM</varname></term>
<listitem><para>Not enough memory to allocate an object.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>-EINVAL</varname></term>
<listitem><para>An invalid argument has been passed. This includes
specyfing an empty mask in <parameter>options</parameter> or a mask
which constains values different than a combination of
<constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
<constant>WCONTINUED</constant>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>-EBUSY</varname></term>
<listitem><para>An handler is already installed for this
child.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>-ESTALE</varname></term>
<listitem><para>The event loop is already terminated.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>-ECHILD</varname></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_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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