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514094f9 | 1 | <?xml version='1.0'?> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
edf25737 | 5 | |
dc83f27a | 6 | <refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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7 | |
8 | <refentryinfo> | |
9 | <title>sd_event_add_child</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_event_add_child</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_event_add_child</refname> | |
80896433 | 20 | <refname>sd_event_add_child_pidfd</refname> |
edf25737 | 21 | <refname>sd_event_source_get_child_pid</refname> |
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22 | <refname>sd_event_source_get_child_pidfd</refname> |
23 | <refname>sd_event_source_get_child_pidfd_own</refname> | |
24 | <refname>sd_event_source_set_child_pidfd_own</refname> | |
25 | <refname>sd_event_source_get_child_process_own</refname> | |
26 | <refname>sd_event_source_set_child_process_own</refname> | |
27 | <refname>sd_event_source_send_child_signal</refname> | |
dc83f27a | 28 | <refname>sd_event_child_handler_t</refname> |
edf25737 | 29 | |
dc83f27a | 30 | <refpurpose>Add a child process state change event source to an event loop</refpurpose> |
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31 | </refnamediv> |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
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35 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
36 | ||
37 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
38 | ||
39 | <funcprototype> | |
40 | <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef> | |
41 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
42 | <paramdef>const siginfo_t *<parameter>si</parameter></paramdef> | |
43 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
44 | </funcprototype> | |
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45 | |
46 | <funcprototype> | |
47 | <funcdef>int <function>sd_event_add_child</function></funcdef> | |
48 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
49 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
50 | <paramdef>pid_t <parameter>pid</parameter></paramdef> | |
51 | <paramdef>int <parameter>options</parameter></paramdef> | |
52 | <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef> | |
53 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
54 | </funcprototype> | |
55 | ||
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56 | <funcprototype> |
57 | <funcdef>int <function>sd_event_add_child_pidfd</function></funcdef> | |
58 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
59 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
60 | <paramdef>int <parameter>pidfd</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 | ||
edf25737 ZJS |
66 | <funcprototype> |
67 | <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef> | |
68 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
69 | <paramdef>pid_t *<parameter>pid</parameter></paramdef> | |
70 | </funcprototype> | |
71 | ||
80896433 LP |
72 | <funcprototype> |
73 | <funcdef>int <function>sd_event_source_get_child_pidfd</function></funcdef> | |
74 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
75 | </funcprototype> | |
76 | ||
77 | <funcprototype> | |
78 | <funcdef>int <function>sd_event_source_get_child_pidfd_own</function></funcdef> | |
79 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
80 | </funcprototype> | |
81 | ||
82 | <funcprototype> | |
83 | <funcdef>int <function>sd_event_source_set_child_pidfd_own</function></funcdef> | |
84 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
85 | <paramdef>int <parameter>own</parameter></paramdef> | |
86 | </funcprototype> | |
87 | ||
88 | <funcprototype> | |
89 | <funcdef>int <function>sd_event_source_get_child_process_own</function></funcdef> | |
90 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
91 | </funcprototype> | |
92 | ||
93 | <funcprototype> | |
94 | <funcdef>int <function>sd_event_source_set_child_process_own</function></funcdef> | |
95 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
96 | <paramdef>int <parameter>own</parameter></paramdef> | |
97 | </funcprototype> | |
98 | ||
99 | <funcprototype> | |
100 | <funcdef>int <function>sd_event_source_send_child_signal</function></funcdef> | |
101 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
102 | <paramdef>int <parameter>sig</parameter></paramdef> | |
103 | <paramdef>const siginfo_t *<parameter>info</parameter></paramdef> | |
104 | <paramdef>unsigned <parameter>flags</parameter></paramdef> | |
105 | </funcprototype> | |
106 | ||
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107 | </funcsynopsis> |
108 | </refsynopsisdiv> | |
109 | ||
110 | <refsect1> | |
111 | <title>Description</title> | |
112 | ||
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113 | <para><function>sd_event_add_child()</function> adds a new child process state change event source to an |
114 | event loop. The event loop object is specified in the <parameter>event</parameter> parameter, the event | |
115 | source object is returned in the <parameter>source</parameter> parameter. The <parameter>pid</parameter> | |
116 | parameter specifies the PID of the process to watch, which must be a direct child process of the invoking | |
117 | process. The <parameter>handler</parameter> must reference a function to call when the process changes | |
118 | state. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be | |
119 | chosen freely by the caller. The handler also receives a pointer to a <structname>siginfo_t</structname> | |
120 | structure containing information about the child process event. The <parameter>options</parameter> | |
121 | parameter determines which state changes will be watched for. It must contain an OR-ed mask of | |
122 | <constant>WEXITED</constant> (watch for the child process terminating), <constant>WSTOPPED</constant> | |
123 | (watch for the child process being stopped by a signal), and <constant>WCONTINUED</constant> (watch for | |
124 | the child process being resumed by a signal). See <citerefentry | |
125 | project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> for | |
126 | further information.</para> | |
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127 | |
128 | <para>Only a single handler may be installed for a specific | |
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129 | child process. The handler is enabled for a single event |
130 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
131 | with | |
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132 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
133 | If the handler function returns a negative error code, it will be | |
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134 | disabled after the invocation, even if the |
135 | <constant>SD_EVENT_ON</constant> mode was requested before. | |
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136 | </para> |
137 | ||
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138 | <para>To destroy an event source object use |
139 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
140 | but note that the event source is only removed from the event loop | |
141 | when all references to the event source are dropped. To make sure | |
142 | an event source does not fire anymore, even when there's still a | |
143 | reference to it kept, consider setting the event source to | |
144 | <constant>SD_EVENT_OFF</constant> with | |
145 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
146 | ||
b3508072 LP |
147 | <para>The <constant>SIGCHLD</constant> signal must be blocked in all threads before this function is |
148 | called (using <citerefentry | |
149 | project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry> or | |
150 | <citerefentry | |
151 | project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>).</para> | |
152 | ||
7f3fdb7f | 153 | <para>If the second parameter of |
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154 | <function>sd_event_add_child()</function> is passed as NULL no |
155 | reference to the event source object is returned. In this case the | |
156 | event source is considered "floating", and will be destroyed | |
157 | implicitly when the event loop itself is destroyed.</para> | |
158 | ||
159 | <para>Note that the <parameter>handler</parameter> function is | |
160 | invoked at a time where the child process is not reaped yet (and | |
161 | thus still is exposed as a zombie process by the kernel). However, | |
162 | the child will be reaped automatically after the function | |
163 | returns. Child processes for which no child process state change | |
164 | event sources are installed will not be reaped by the event loop | |
165 | implementation.</para> | |
166 | ||
167 | <para>If both a child process state change event source and a | |
168 | <constant>SIGCHLD</constant> signal event source is installed in | |
169 | the same event loop, the configured event source priorities decide | |
170 | which event source is dispatched first. If the signal handler is | |
171 | processed first, it should leave the child processes for which | |
172 | child process state change event sources are installed unreaped.</para> | |
173 | ||
80896433 LP |
174 | <para><function>sd_event_add_child_pidfd()</function> is similar to |
175 | <function>sd_event_add_child()</function> but takes a file descriptor referencing the process ("pidfd") | |
176 | instead of the numeric PID. A suitable file descriptor may be acquired via <citerefentry | |
177 | project='man-pages'><refentrytitle>pidfd_open</refentrytitle><manvolnum>2</manvolnum></citerefentry> and | |
178 | related calls. The passed file descriptor is not closed when the event source is freed again, unless | |
179 | <function>sd_event_source_set_child_pidfd_own()</function> is used to turn this behaviour on. Note that | |
180 | regardless which of <function>sd_event_add_child()</function> and | |
181 | <function>sd_event_add_child_pidfd()</function> is used for allocating an event source, the watched | |
182 | process has to be a direct child process of the invoking process. Also in both cases | |
183 | <constant>SIGCHLD</constant> has to be blocked in the invoking process.</para> | |
184 | ||
edf25737 | 185 | <para><function>sd_event_source_get_child_pid()</function> |
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186 | retrieves the configured PID of a child process state change event |
187 | source created previously with | |
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188 | <function>sd_event_add_child()</function>. It takes the event |
189 | source object as the <parameter>source</parameter> parameter and a | |
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190 | pointer to a <type>pid_t</type> variable to return the process ID |
191 | in. | |
edf25737 | 192 | </para> |
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193 | |
194 | <para><function>sd_event_source_get_child_pidfd()</function> retrieves the file descriptor referencing | |
195 | the watched process ("pidfd") if this functionality is available. On kernels that support the concept the | |
196 | event loop will make use of pidfds to watch child processes, regardless if the individual event sources | |
197 | are allocated via <function>sd_event_add_child()</function> or | |
198 | <function>sd_event_add_child_pidfd()</function>. If the latter call was used to allocate the event | |
199 | source, this function returns the file descriptor used for allocation. On kernels that do not support the | |
200 | pidfd concept this function will fail with <constant>EOPNOTSUPP</constant>. This call takes the event | |
201 | source object as the <parameter>source</parameter> parameter and returns the numeric file descriptor. | |
202 | </para> | |
203 | ||
204 | <para><function>sd_event_source_get_child_pidfd_own()</function> may be used to query whether the pidfd | |
205 | the event source encapsulates shall be closed when the event source is freed. This function returns zero | |
206 | if the pidfd shall be left open, and positive if it shall be closed automatically. By default this | |
207 | setting defaults to on if the event source was allocated via <function>sd_event_add_child()</function> | |
208 | and off if it was allocated via <function>sd_event_add_child_pidfd()</function>. The | |
209 | <function>sd_event_source_set_child_pidfd_own()</function> function may be used to change the setting and | |
210 | takes a boolean parameter with the new setting.</para> | |
211 | ||
212 | <para><function>sd_event_source_get_child_process_own()</function> may be used to query whether the | |
213 | process the event source watches shall be killed (with <constant>SIGKILL</constant>) and reaped when the | |
214 | event source is freed. This function returns zero if the process shell be left running, and positive if | |
215 | it shall be killed and reaped automatically. By default this setting defaults to off. The | |
216 | <function>sd_event_source_set_child_process_own()</function> function may be used to change the setting | |
217 | and takes a boolean parameter with the new setting. Note that currently if the calling process is | |
218 | terminated abnormally the watched process might survive even thought the event source ceases to | |
219 | exist. This behaviour might change eventually.</para> | |
220 | ||
221 | <para><function>sd_event_source_send_child_signal()</function> may be used to send a UNIX signal to the | |
222 | watched process. If the pidfd concept is supported in the kernel, this is implemented via <citerefentry | |
223 | project='man-pages'><refentrytitle>pidfd_send_signal</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
224 | and otherwise via <citerefentry | |
225 | project='man-pages'><refentrytitle>rt_sigqueueinfo</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
226 | (or via <citerefentry | |
227 | project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry> in case | |
228 | <parameter>info</parameter> is <constant>NULL</constant>). The specified parameters match those of these | |
229 | underlying system calls, except that the <parameter>info</parameter> is never modified (and is thus | |
230 | declared constant). Like for the underlying system calls, the <parameter>flags</parameter> parameter | |
231 | currently must be zero.</para> | |
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232 | </refsect1> |
233 | ||
234 | <refsect1> | |
235 | <title>Return Value</title> | |
236 | ||
237 | <para>On success, these functions return 0 or a positive | |
238 | integer. On failure, they return a negative errno-style error | |
239 | code.</para> | |
edf25737 | 240 | |
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241 | <refsect2> |
242 | <title>Errors</title> | |
edf25737 | 243 | |
b1de39de | 244 | <para>Returned errors may indicate the following problems:</para> |
edf25737 | 245 | |
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246 | <variablelist> |
247 | <varlistentry> | |
248 | <term><constant>-ENOMEM</constant></term> | |
edf25737 | 249 | |
b1de39de ZJS |
250 | <listitem><para>Not enough memory to allocate an object.</para></listitem> |
251 | </varlistentry> | |
edf25737 | 252 | |
b1de39de ZJS |
253 | <varlistentry> |
254 | <term><constant>-EINVAL</constant></term> | |
edf25737 | 255 | |
b1de39de ZJS |
256 | <listitem><para>An invalid argument has been passed. This includes |
257 | specifying an empty mask in <parameter>options</parameter> or a mask | |
258 | which contains values different than a combination of | |
259 | <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and | |
260 | <constant>WCONTINUED</constant>. | |
261 | </para></listitem> | |
edf25737 | 262 | |
b1de39de | 263 | </varlistentry> |
edf25737 | 264 | |
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265 | <varlistentry> |
266 | <term><constant>-EBUSY</constant></term> | |
edf25737 | 267 | |
b3508072 LP |
268 | <listitem><para>A handler is already installed for this child process, or |
269 | <constant>SIGCHLD</constant> is not blocked.</para></listitem> | |
edf25737 | 270 | |
b1de39de | 271 | </varlistentry> |
edf25737 | 272 | |
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273 | <varlistentry> |
274 | <term><constant>-ESTALE</constant></term> | |
edf25737 | 275 | |
b1de39de | 276 | <listitem><para>The event loop is already terminated.</para></listitem> |
edf25737 | 277 | |
b1de39de | 278 | </varlistentry> |
edf25737 | 279 | |
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280 | <varlistentry> |
281 | <term><constant>-ECHILD</constant></term> | |
edf25737 | 282 | |
b1de39de | 283 | <listitem><para>The event loop has been created in a different process.</para></listitem> |
edf25737 | 284 | |
b1de39de | 285 | </varlistentry> |
edf25737 | 286 | |
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287 | <varlistentry> |
288 | <term><constant>-EDOM</constant></term> | |
edf25737 | 289 | |
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290 | <listitem><para>The passed event source is not a child process event source.</para></listitem> |
291 | </varlistentry> | |
edf25737 | 292 | |
80896433 LP |
293 | <varlistentry> |
294 | <term><constant>-EOPNOTSUPP</constant></term> | |
295 | ||
296 | <listitem><para>A pidfd was requested but the kernel does not support this concept.</para></listitem> | |
297 | </varlistentry> | |
298 | ||
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299 | </variablelist> |
300 | </refsect2> | |
edf25737 ZJS |
301 | </refsect1> |
302 | ||
dc83f27a LP |
303 | <xi:include href="libsystemd-pkgconfig.xml" /> |
304 | ||
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305 | <refsect1> |
306 | <title>See Also</title> | |
307 | ||
308 | <para> | |
309 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
310 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
311 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
dc83f27a LP |
312 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
313 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
edf25737 ZJS |
314 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
315 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 316 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
4dfefc19 | 317 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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318 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
319 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
320 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
321 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
0bca2831 | 322 | <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
b3508072 LP |
323 | <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>, |
324 | <citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
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325 | <citerefentry project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
326 | <citerefentry project='man-pages'><refentrytitle>pidfd_open</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
327 | <citerefentry project='man-pages'><refentrytitle>pidfd_send_signal</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
328 | <citerefentry project='man-pages'><refentrytitle>rt_sigqueueinfo</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
329 | <citerefentry project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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330 | </para> |
331 | </refsect1> | |
332 | ||
333 | </refentry> |