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The meaning of the return value, the default handlers, and loop exiting are now described.
203 lines
9.8 KiB
XML
203 lines
9.8 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_event_add_defer" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_defer</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_add_defer</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_add_defer</refname>
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<refname>sd_event_add_post</refname>
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<refname>sd_event_add_exit</refname>
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<refname>sd_event_handler_t</refname>
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<refpurpose>Add static event sources to an event loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_defer</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_post</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_exit</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>These three functions add new static event sources to an event loop. The event loop object is
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specified in the <parameter>event</parameter> parameter, the event source object is returned in the
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<parameter>source</parameter> parameter. The event sources are enabled statically and will "fire" when
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the event loop is run and the conditions described below are met.</para>
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<para>The <parameter>handler</parameter> is a function to call or <constant>NULL</constant>. The handler
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function will be passed the <parameter>userdata</parameter> pointer, which may be chosen freely by the
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caller. The handler may return negative to signal an error (see below), other return values are
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ignored. If <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
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used.</para>
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<para><function>sd_event_add_defer()</function> adds a new event
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source that will be dispatched instantly, before the event loop
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goes to sleep again and waits for new events. By default, the
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handler will be called once
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(<constant>SD_EVENT_ONESHOT</constant>). Note that if the event
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source is set to <constant>SD_EVENT_ON</constant> the event loop
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will never go to sleep again, but continuously call the handler,
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possibly interleaved with other event sources.</para>
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<para><function>sd_event_add_post()</function> adds a new event
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source that is run before the event loop will sleep and wait
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for new events, but only after at least one other non-post event
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source was dispatched. By default, the source is enabled
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permanently (<constant>SD_EVENT_ON</constant>). Note that this
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event source type will still allow the event loop to go to sleep
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again, even if set to <constant>SD_EVENT_ON</constant>, as long as
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no other event source is ever triggered.</para>
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<para><function>sd_event_add_exit()</function> adds a new event
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source that will be dispatched when the event loop is terminated
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with <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>The
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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function may be used to enable the event source permanently
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(<constant>SD_EVENT_ON</constant>) or to make it fire just once
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(<constant>SD_EVENT_ONESHOT</constant>).</para>
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<para>If the handler function returns a negative error code, it will either be disabled after the
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invocation, even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the
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loop to terminate, see
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<citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but note that the event source is only removed from the event loop
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when all references to the event source are dropped. To make sure
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an event source does not fire anymore, even when there's still a
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reference to it kept, consider setting the event source to
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<constant>SD_EVENT_OFF</constant> with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the second parameter of these functions is passed as <constant>NULL</constant> no reference to
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the event source object is returned. In this case the event source is considered "floating", and will be
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destroyed implicitly when the event loop itself is destroyed.</para>
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<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_defer()</function> or
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<function>sd_event_add_post()</function> is <constant>NULL</constant>, and the event source fires, this
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will be considered a request to exit the event loop. In this case, the <parameter>userdata</parameter>
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parameter, cast to an integer, is passed as the exit code parameter to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Similar
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functionality is not available for <function>sd_event_add_exit()</function>, as these types of event
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sources are only dispatched when exiting anyway.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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