mirror of
https://github.com/systemd/systemd-stable.git
synced 2024-12-23 17:34:00 +03:00
5ca99dfabd
The thing with blocking SIGCHLD is rather annoying. I think we could/should make this automatic.
353 lines
19 KiB
XML
353 lines
19 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_event_add_child</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>sd_event_add_child</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>sd_event_add_child</refname>
|
|
<refname>sd_event_add_child_pidfd</refname>
|
|
<refname>sd_event_source_get_child_pid</refname>
|
|
<refname>sd_event_source_get_child_pidfd</refname>
|
|
<refname>sd_event_source_get_child_pidfd_own</refname>
|
|
<refname>sd_event_source_set_child_pidfd_own</refname>
|
|
<refname>sd_event_source_get_child_process_own</refname>
|
|
<refname>sd_event_source_set_child_process_own</refname>
|
|
<refname>sd_event_source_send_child_signal</refname>
|
|
<refname>sd_event_child_handler_t</refname>
|
|
|
|
<refpurpose>Add a child process state change event source to an event loop</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
|
|
|
|
<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
|
|
|
|
<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_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>int <function>sd_event_add_child_pidfd</function></funcdef>
|
|
<paramdef>sd_event *<parameter>event</parameter></paramdef>
|
|
<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
|
|
<paramdef>int <parameter>pidfd</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>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>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_get_child_pidfd</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_get_child_pidfd_own</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_set_child_pidfd_own</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
<paramdef>int <parameter>own</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_get_child_process_own</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_set_child_process_own</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
<paramdef>int <parameter>own</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_send_child_signal</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
<paramdef>int <parameter>sig</parameter></paramdef>
|
|
<paramdef>const siginfo_t *<parameter>info</parameter></paramdef>
|
|
<paramdef>unsigned <parameter>flags</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para><function>sd_event_add_child()</function> adds a new child process state change event source to an
|
|
event loop. The event loop object is specified in the <parameter>event</parameter> parameter, the event
|
|
source object is returned in the <parameter>source</parameter> parameter. The <parameter>pid</parameter>
|
|
parameter specifies the PID of the process to watch, which must be a direct child process of the invoking
|
|
process. 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 process terminating),
|
|
<constant>WSTOPPED</constant> (watch for the child process being stopped by a signal), and
|
|
<constant>WCONTINUED</constant> (watch for the child process being resumed by a signal). See
|
|
<citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
|
|
for further information.</para>
|
|
|
|
<para>The <parameter>handler</parameter> must be a function to call when the process changes state or
|
|
<constant>NULL</constant>. 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>siginfo_t</structname> structure containing information about the child process event. The
|
|
handler may return negative to signal an error (see below), other return values are ignored. If
|
|
<parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
|
|
<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
|
|
used.</para>
|
|
|
|
<para>Only a single handler may be installed for a specific child process. 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 either be disabled after the invocation,
|
|
even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to
|
|
terminate, see
|
|
<citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
|
|
</para>
|
|
|
|
<para>To destroy an event source object use
|
|
<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
but note that the event source is only removed from the event loop
|
|
when all references to the event source are dropped. To make sure
|
|
an event source does not fire anymore, even when there's still a
|
|
reference to it kept, consider setting the event source to
|
|
<constant>SD_EVENT_OFF</constant> with
|
|
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
|
|
|
|
<para>The <constant>SIGCHLD</constant> signal must be blocked in all threads before this function is
|
|
called (using <citerefentry
|
|
project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
|
|
<citerefentry
|
|
project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>).</para>
|
|
|
|
<para>If the second parameter of <function>sd_event_add_child()</function> is passed as
|
|
<constant>NULL</constant> no reference to the event source object is returned. In this case the event
|
|
source is considered "floating", and will be destroyed implicitly when the event loop itself is
|
|
destroyed.</para>
|
|
|
|
<para>Note that the <parameter>handler</parameter> function is
|
|
invoked at a time where the child process is not reaped yet (and
|
|
thus still is exposed as a zombie process by the kernel). However,
|
|
the child will be reaped automatically after the function
|
|
returns. Child processes for which no child process state change
|
|
event sources are installed will not be reaped by the event loop
|
|
implementation.</para>
|
|
|
|
<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_child()</function> is
|
|
<constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
|
|
event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
|
|
the exit code parameter to
|
|
<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
|
|
|
|
<para>If both a child process state change event source and a
|
|
<constant>SIGCHLD</constant> signal event source is installed in
|
|
the same event loop, the configured event source priorities decide
|
|
which event source is dispatched first. If the signal handler is
|
|
processed first, it should leave the child processes for which
|
|
child process state change event sources are installed unreaped.</para>
|
|
|
|
<para><function>sd_event_add_child_pidfd()</function> is similar to
|
|
<function>sd_event_add_child()</function> but takes a file descriptor referencing the process ("pidfd")
|
|
instead of the numeric PID. A suitable file descriptor may be acquired via <citerefentry
|
|
project='man-pages'><refentrytitle>pidfd_open</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
|
|
related calls. The passed file descriptor is not closed when the event source is freed again, unless
|
|
<function>sd_event_source_set_child_pidfd_own()</function> is used to turn this behaviour on. Note that
|
|
regardless which of <function>sd_event_add_child()</function> and
|
|
<function>sd_event_add_child_pidfd()</function> is used for allocating an event source, the watched
|
|
process has to be a direct child process of the invoking process. Also in both cases
|
|
<constant>SIGCHLD</constant> has to be blocked in the invoking process.</para>
|
|
|
|
<para><function>sd_event_source_get_child_pid()</function>
|
|
retrieves the configured PID of a child process 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 a <type>pid_t</type> variable to return the process ID
|
|
in.
|
|
</para>
|
|
|
|
<para><function>sd_event_source_get_child_pidfd()</function> retrieves the file descriptor referencing
|
|
the watched process ("pidfd") if this functionality is available. On kernels that support the concept the
|
|
event loop will make use of pidfds to watch child processes, regardless if the individual event sources
|
|
are allocated via <function>sd_event_add_child()</function> or
|
|
<function>sd_event_add_child_pidfd()</function>. If the latter call was used to allocate the event
|
|
source, this function returns the file descriptor used for allocation. On kernels that do not support the
|
|
pidfd concept this function will fail with <constant>EOPNOTSUPP</constant>. This call takes the event
|
|
source object as the <parameter>source</parameter> parameter and returns the numeric file descriptor.
|
|
</para>
|
|
|
|
<para><function>sd_event_source_get_child_pidfd_own()</function> may be used to query whether the pidfd
|
|
the event source encapsulates shall be closed when the event source is freed. This function returns zero
|
|
if the pidfd shall be left open, and positive if it shall be closed automatically. By default this
|
|
setting defaults to on if the event source was allocated via <function>sd_event_add_child()</function>
|
|
and off if it was allocated via <function>sd_event_add_child_pidfd()</function>. The
|
|
<function>sd_event_source_set_child_pidfd_own()</function> function may be used to change the setting and
|
|
takes a boolean parameter with the new setting.</para>
|
|
|
|
<para><function>sd_event_source_get_child_process_own()</function> may be used to query whether the
|
|
process the event source watches shall be killed (with <constant>SIGKILL</constant>) and reaped when the
|
|
event source is freed. This function returns zero if the process shell be left running, and positive if
|
|
it shall be killed and reaped automatically. By default this setting defaults to off. The
|
|
<function>sd_event_source_set_child_process_own()</function> function may be used to change the setting
|
|
and takes a boolean parameter with the new setting. Note that currently if the calling process is
|
|
terminated abnormally the watched process might survive even thought the event source ceases to
|
|
exist. This behaviour might change eventually.</para>
|
|
|
|
<para><function>sd_event_source_send_child_signal()</function> may be used to send a UNIX signal to the
|
|
watched process. If the pidfd concept is supported in the kernel, this is implemented via <citerefentry
|
|
project='man-pages'><refentrytitle>pidfd_send_signal</refentrytitle><manvolnum>2</manvolnum></citerefentry>
|
|
and otherwise via <citerefentry
|
|
project='man-pages'><refentrytitle>rt_sigqueueinfo</refentrytitle><manvolnum>2</manvolnum></citerefentry>
|
|
(or via <citerefentry
|
|
project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry> in case
|
|
<parameter>info</parameter> is <constant>NULL</constant>). The specified parameters match those of these
|
|
underlying system calls, except that the <parameter>info</parameter> is never modified (and is thus
|
|
declared constant). Like for the underlying system calls, the <parameter>flags</parameter> parameter
|
|
currently must be zero.</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>
|
|
|
|
<refsect2>
|
|
<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
|
|
specifying 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>A handler is already installed for this child process, or
|
|
<constant>SIGCHLD</constant> is not blocked.</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>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EDOM</constant></term>
|
|
|
|
<listitem><para>The passed event source is not a child process event source.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EOPNOTSUPP</constant></term>
|
|
|
|
<listitem><para>A pidfd was requested but the kernel does not support this concept.</para></listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" />
|
|
|
|
<refsect1>
|
|
<title>Example</title>
|
|
|
|
<example>
|
|
<title>Exit loop when the child terminates</title>
|
|
|
|
<programlisting><xi:include href="event-quick-child.c" parse="text" /></programlisting>
|
|
</example>
|
|
</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_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_event_add_io</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_inotify</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>,
|
|
<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>pidfd_open</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>pidfd_send_signal</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>rt_sigqueueinfo</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
|
|
<citerefentry project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|