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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
146 lines
6.4 KiB
XML
146 lines
6.4 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+ -->
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<refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_set_watchdog</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_set_watchdog</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_set_watchdog</refname>
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<refname>sd_event_get_watchdog</refname>
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<refpurpose>Enable event loop watchdog support</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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<funcprototype>
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<funcdef>int <function>sd_event_set_watchdog</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>int b</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_get_watchdog</function></funcdef>
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<paramdef>sd_event *<parameter>event</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><function>sd_event_set_watchdog()</function> may be used to
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enable or disable automatic watchdog notification support in the
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event loop object specified in the <parameter>event</parameter>
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parameter. Specifically, depending on the <parameter>b</parameter>
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boolean argument this will make sure the event loop wakes up in
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regular intervals and sends watchdog notification messages to the
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service manager, if this was requested by the service
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manager. Watchdog support is determined with
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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and watchdog messages are sent with
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See
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the <varname>WatchdogSec=</varname> setting in
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details on how to enable watchdog support for a service and
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the protocol used. The wake-up interval is chosen as half the
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watchdog timeout declared by the service manager via the
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<varname>$WATCHDOG_USEC</varname> environment variable. If the
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service manager did not request watchdog notifications, or if the
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process was not invoked by the service manager this call with a
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true <parameter>b</parameter> parameter executes no
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operation. Passing a false <parameter>b</parameter> parameter will
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disable the automatic sending of watchdog notification messages if
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it was enabled before. Newly allocated event loop objects have
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this feature disabled.</para>
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<para>The first watchdog notification message is sent immediately
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when <function>set_event_set_watchdog()</function> is invoked with
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a true <parameter>b</parameter> parameter.</para>
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<para>The watchdog logic is designed to allow the service manager
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to automatically detect services that ceased processing of
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incoming events, and thus appear "hung". Watchdog notifications
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are sent out only at the beginning of each event loop
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iteration. If an event source dispatch function blocks for an
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excessively long time and does not return execution to the event
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loop quickly, this might hence cause the notification message to
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be delayed, and possibly result in abnormal program termination,
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as configured in the service unit file.</para>
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<para><function>sd_event_get_watchdog()</function> may be used to
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determine whether watchdog support was previously requested by a
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call to <function>sd_event_set_watchdog()</function> with a true
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<parameter>b</parameter> parameter and successfully
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enabled.</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, <function>sd_event_set_watchdog()</function> and
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<function>sd_event_get_watchdog()</function> return a non-zero positive integer if the service manager
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requested watchdog support and watchdog support was successfully enabled. They return zero if the service
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manager did not request watchdog support, or if watchdog support was explicitly disabled with a false
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<parameter>b</parameter> parameter. On failure, they return a negative errno-style error 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>-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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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>The passed event loop object was invalid.</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_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_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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