Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 368 insertions, 0 deletions

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+<?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 &lt;systemd/sd-event.h&gt;</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, library or module instance.</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>
+
+          <xi:include href="version-info.xml" xpointer="v245"/></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>History</title>
+    <para><function>sd_event_add_child()</function>,
+    <function>sd_event_child_handler_t()</function>, and
+    <function>sd_event_source_get_child_pid()</function> were added in version 217.</para>
+    <para><function>sd_event_add_child_pidfd()</function>,
+    <function>sd_event_source_get_child_pidfd()</function>,
+    <function>sd_event_source_get_child_pidfd_own()</function>,
+    <function>sd_event_source_set_child_pidfd_own()</function>,
+    <function>sd_event_source_get_child_process_own()</function>,
+    <function>sd_event_source_set_child_process_own()</function>, and
+    <function>sd_event_source_send_child_signal()</function> were added in version 245.</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_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>