Prep v233.3: Add missing documentation for API functions exported by elogind. (unreviewed)

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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2014 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_event_add_time</title>
+    <productname>systemd</productname>
+
+    <authorgroup>
+      <author>
+        <contrib>Developer</contrib>
+        <firstname>Lennart</firstname>
+        <surname>Poettering</surname>
+        <email>lennart@poettering.net</email>
+      </author>
+    </authorgroup>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_event_add_time</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_event_add_time</refname>
+    <refname>sd_event_source_get_time</refname>
+    <refname>sd_event_source_set_time</refname>
+    <refname>sd_event_source_get_time_accuracy</refname>
+    <refname>sd_event_source_set_time_accuracy</refname>
+    <refname>sd_event_source_get_time_clock</refname>
+    <refname>sd_event_time_handler_t</refname>
+
+    <refpurpose>Add a timer 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_time_handler_t</function>)</funcdef>
+        <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
+        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
+        <paramdef>void *<parameter>userdata</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_add_time</function></funcdef>
+        <paramdef>sd_event *<parameter>event</parameter></paramdef>
+        <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
+        <paramdef>clockid_t <parameter>clock</parameter></paramdef>
+        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
+        <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
+        <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
+        <paramdef>void *<parameter>userdata</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_time</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_set_time</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
+      </funcprototype>
+
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><function>sd_event_add_time()</function> adds a new timer 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>clock</parameter> parameter takes a clock identifier, one
+    of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
+    <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
+    <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
+    regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
+    microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
+    is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
+    dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
+    which may be used as an alternative to explicitly disabling a timer event source with
+    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
+    <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
+    timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
+    accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
+    substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
+    improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
+    the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
+    chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
+    slightly later, subject to the specified accuracy value, the kernel timer slack (see
+    <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
+    scheduling latencies. To query the actual time the handler was called use
+    <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+    <para>By default, the timer will elapse once
+    (<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 be
+    disabled after the invocation, even if the
+    <constant>SD_EVENT_ON</constant> mode was requested before. Note
+    that a timer event set to <constant>SD_EVENT_ON</constant> will
+    fire continuously unless its configured time is updated using
+    <function>sd_event_source_set_time()</function>.
+    </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 if it is still referenced,
+    disable the event source using
+    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    with <constant>SD_EVENT_OFF</constant>.</para>
+
+    <para>If the second parameter of
+    <function>sd_event_add_time()</function> is
+    <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>If the <parameter>handler</parameter> to
+    <function>sd_event_add_time()</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
+    used for the exit code passed to
+    <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+    <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
+    <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
+    that may wake up the system from suspend.</para>
+
+    <para>In order to set up relative timers (that is, relative to the
+    current time), retrieve the current time via
+    <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+    add the desired timespan to it, and use the result as
+    the <parameter>usec</parameter> parameter to
+    <function>sd_event_add_time()</function>.</para>
+
+    <para>In order to set up repetitive timers (that is, timers that
+    are triggered in regular intervals), set up the timer normally,
+    for the first invocation. Each time the event handler is invoked,
+    update the timer's trigger time with
+    <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
+    iteration, and reenable the timer using
+    <function>sd_event_source_set_enabled()</function>. To calculate
+    the next point in time to pass to
+    <function>sd_event_source_set_time()</function>, either use as
+    base the <parameter>usec</parameter> parameter passed to the timer
+    callback, or the timestamp returned by
+    <function>sd_event_now()</function>. In the former case timer
+    events will be regular, while in the latter case the scheduling
+    latency will keep accumulating on the timer.</para>
+
+    <para><function>sd_event_source_get_time()</function> retrieves
+    the configured time value of an event source created
+    previously with <function>sd_event_add_time()</function>. It takes
+    the event source object and a pointer to a variable to store the
+    time in, relative to the selected clock's epoch, in µs.</para>
+
+    <para><function>sd_event_source_set_time()</function> changes the
+    time of an event source created previously with
+    <function>sd_event_add_time()</function>. It takes the event
+    source object and a time relative to the selected clock's epoch,
+    in µs.</para>
+
+    <para><function>sd_event_source_get_time_accuracy()</function>
+    retrieves the configured accuracy value of an event source
+    created previously with <function>sd_event_add_time()</function>. It
+    takes the event source object and a pointer to a variable to store
+    the accuracy in. The accuracy is specified in µs.</para>
+
+    <para><function>sd_event_source_set_time_accuracy()</function>
+    changes the configured accuracy of a timer event source created
+    previously with <function>sd_event_add_time()</function>. It takes
+    the event source object and accuracy, in µs.</para>
+
+    <para><function>sd_event_source_get_time_clock()</function>
+    retrieves the configured clock of an event source created
+    previously with <function>sd_event_add_time()</function>. It takes
+    the event source object and a pointer to a variable to store the
+    clock identifier in.</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>
+  </refsect1>
+
+  <refsect1>
+    <title>Errors</title>
+
+    <para>Returned values 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.</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>-EOPNOTSUPP</constant></term>
+
+        <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
+
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-EDOM</constant></term>
+
+        <listitem><para>The passed event source is not a timer event source.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <xi:include href="libelogind-pkgconfig.xml" />
+
+  <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_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_child</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 project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>