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diff --git a/man/sd_event_add_child.xml b/man/sd_event_add_child.xml new file mode 100644 index 0000000..fec754d --- /dev/null +++ b/man/sd_event_add_child.xml @@ -0,0 +1,352 @@ +<?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> |