man: add sd_event_add_child(3)

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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 &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 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>