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514094f9 | 1 | <?xml version='1.0'?> |
edf25737 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
dc83f27a | 9 | <refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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10 | |
11 | <refentryinfo> | |
12 | <title>sd_event_add_child</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_event_add_child</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_event_add_child</refname> | |
23 | <refname>sd_event_source_get_child_pid</refname> | |
dc83f27a | 24 | <refname>sd_event_child_handler_t</refname> |
edf25737 | 25 | |
dc83f27a | 26 | <refpurpose>Add a child process state change event source to an event loop</refpurpose> |
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27 | </refnamediv> |
28 | ||
29 | <refsynopsisdiv> | |
30 | <funcsynopsis> | |
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31 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
32 | ||
33 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
34 | ||
35 | <funcprototype> | |
36 | <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef> | |
37 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
38 | <paramdef>const siginfo_t *<parameter>si</parameter></paramdef> | |
39 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
40 | </funcprototype> | |
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41 | |
42 | <funcprototype> | |
43 | <funcdef>int <function>sd_event_add_child</function></funcdef> | |
44 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
45 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
46 | <paramdef>pid_t <parameter>pid</parameter></paramdef> | |
47 | <paramdef>int <parameter>options</parameter></paramdef> | |
48 | <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef> | |
49 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
50 | </funcprototype> | |
51 | ||
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52 | <funcprototype> |
53 | <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef> | |
54 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
55 | <paramdef>pid_t *<parameter>pid</parameter></paramdef> | |
56 | </funcprototype> | |
57 | ||
58 | </funcsynopsis> | |
59 | </refsynopsisdiv> | |
60 | ||
61 | <refsect1> | |
62 | <title>Description</title> | |
63 | ||
64 | <para><function>sd_event_add_child()</function> adds a new child | |
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65 | process state change event source to an event loop. The event loop |
66 | object is specified in the <parameter>event</parameter> parameter, | |
67 | the event source object is returned in the | |
68 | <parameter>source</parameter> parameter. The | |
69 | <parameter>pid</parameter> parameter specifies the PID of the | |
70 | process to watch. The <parameter>handler</parameter> must | |
71 | reference a function to call when the process changes state. The | |
72 | handler function will be passed the | |
73 | <parameter>userdata</parameter> pointer, which may be chosen | |
74 | freely by the caller. The handler also receives a pointer to a | |
75 | <structname>siginfo_t</structname> structure containing | |
76 | information about the child process event. The | |
77 | <parameter>options</parameter> parameter determines which state | |
78 | changes will be watched for. It must contain an OR-ed mask of | |
79 | <constant>WEXITED</constant> (watch for the child process | |
edf25737 | 80 | terminating), <constant>WSTOPPED</constant> (watch for the child |
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81 | process being stopped by a signal), and |
82 | <constant>WCONTINUED</constant> (watch for the child process being | |
83 | resumed by a signal). See <citerefentry | |
84 | project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
922d948b | 85 | for further information.</para> |
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86 | |
87 | <para>Only a single handler may be installed for a specific | |
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88 | child process. The handler is enabled for a single event |
89 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
90 | with | |
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91 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
92 | If the handler function returns a negative error code, it will be | |
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93 | disabled after the invocation, even if the |
94 | <constant>SD_EVENT_ON</constant> mode was requested before. | |
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95 | </para> |
96 | ||
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97 | <para>To destroy an event source object use |
98 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
99 | but note that the event source is only removed from the event loop | |
100 | when all references to the event source are dropped. To make sure | |
101 | an event source does not fire anymore, even when there's still a | |
102 | reference to it kept, consider setting the event source to | |
103 | <constant>SD_EVENT_OFF</constant> with | |
104 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
105 | ||
7f3fdb7f | 106 | <para>If the second parameter of |
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107 | <function>sd_event_add_child()</function> is passed as NULL no |
108 | reference to the event source object is returned. In this case the | |
109 | event source is considered "floating", and will be destroyed | |
110 | implicitly when the event loop itself is destroyed.</para> | |
111 | ||
112 | <para>Note that the <parameter>handler</parameter> function is | |
113 | invoked at a time where the child process is not reaped yet (and | |
114 | thus still is exposed as a zombie process by the kernel). However, | |
115 | the child will be reaped automatically after the function | |
116 | returns. Child processes for which no child process state change | |
117 | event sources are installed will not be reaped by the event loop | |
118 | implementation.</para> | |
119 | ||
120 | <para>If both a child process state change event source and a | |
121 | <constant>SIGCHLD</constant> signal event source is installed in | |
122 | the same event loop, the configured event source priorities decide | |
123 | which event source is dispatched first. If the signal handler is | |
124 | processed first, it should leave the child processes for which | |
125 | child process state change event sources are installed unreaped.</para> | |
126 | ||
edf25737 | 127 | <para><function>sd_event_source_get_child_pid()</function> |
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128 | retrieves the configured PID of a child process state change event |
129 | source created previously with | |
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130 | <function>sd_event_add_child()</function>. It takes the event |
131 | source object as the <parameter>source</parameter> parameter and a | |
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132 | pointer to a <type>pid_t</type> variable to return the process ID |
133 | in. | |
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134 | </para> |
135 | </refsect1> | |
136 | ||
137 | <refsect1> | |
138 | <title>Return Value</title> | |
139 | ||
140 | <para>On success, these functions return 0 or a positive | |
141 | integer. On failure, they return a negative errno-style error | |
142 | code.</para> | |
143 | </refsect1> | |
144 | ||
145 | <refsect1> | |
146 | <title>Errors</title> | |
147 | ||
148 | <para>Returned errors may indicate the following problems:</para> | |
149 | ||
150 | <variablelist> | |
151 | <varlistentry> | |
8474b70c | 152 | <term><constant>-ENOMEM</constant></term> |
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153 | |
154 | <listitem><para>Not enough memory to allocate an object.</para></listitem> | |
155 | </varlistentry> | |
156 | ||
157 | <varlistentry> | |
8474b70c | 158 | <term><constant>-EINVAL</constant></term> |
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159 | |
160 | <listitem><para>An invalid argument has been passed. This includes | |
cc98b302 | 161 | specifying an empty mask in <parameter>options</parameter> or a mask |
f131770b | 162 | which contains values different than a combination of |
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163 | <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and |
164 | <constant>WCONTINUED</constant>. | |
165 | </para></listitem> | |
166 | ||
167 | </varlistentry> | |
168 | ||
169 | <varlistentry> | |
8474b70c | 170 | <term><constant>-EBUSY</constant></term> |
edf25737 | 171 | |
a8eaaee7 | 172 | <listitem><para>A handler is already installed for this |
dc83f27a | 173 | child process.</para></listitem> |
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174 | |
175 | </varlistentry> | |
176 | ||
177 | <varlistentry> | |
8474b70c | 178 | <term><constant>-ESTALE</constant></term> |
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179 | |
180 | <listitem><para>The event loop is already terminated.</para></listitem> | |
181 | ||
182 | </varlistentry> | |
183 | ||
184 | <varlistentry> | |
8474b70c | 185 | <term><constant>-ECHILD</constant></term> |
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186 | |
187 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
188 | ||
189 | </varlistentry> | |
190 | ||
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191 | <varlistentry> |
192 | <term><constant>-EDOM</constant></term> | |
edf25737 | 193 | |
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194 | <listitem><para>The passed event source is not a child process event source.</para></listitem> |
195 | </varlistentry> | |
edf25737 | 196 | |
dc83f27a | 197 | </variablelist> |
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198 | </refsect1> |
199 | ||
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200 | <xi:include href="libsystemd-pkgconfig.xml" /> |
201 | ||
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202 | <refsect1> |
203 | <title>See Also</title> | |
204 | ||
205 | <para> | |
206 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
207 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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209 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
210 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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211 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
212 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 213 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
4dfefc19 | 214 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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215 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
216 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
217 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
218 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
219 | <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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220 | </para> |
221 | </refsect1> | |
222 | ||
223 | </refentry> |