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149 lines
6.6 KiB
XML
149 lines
6.6 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_source_set_ratelimit" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_source_set_ratelimit</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_source_set_ratelimit</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_source_set_ratelimit</refname>
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<refname>sd_event_source_get_ratelimit</refname>
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<refname>sd_event_source_is_ratelimited</refname>
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<refpurpose>Configure rate limiting on event sources</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_source_set_ratelimit</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>interval_usec</parameter></paramdef>
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<paramdef>unsigned <parameter>burst</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_ratelimit</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t* <parameter>ret_interval_usec</parameter></paramdef>
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<paramdef>unsigned* <parameter>ret_burst</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_is_ratelimited</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</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_source_set_ratelimit()</function> may be used to enforce rate limiting on an
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event source. When used an event source will be temporarily turned off when it fires more often then a
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specified burst number within a specified time interval. This is useful as simple mechanism to avoid
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event source starvation if high priority event sources fire very frequently.</para>
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<para>Pass the event source to operate on as first argument, a time interval in microseconds as second
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argument and a maximum dispatch limit ("burst") as third parameter. Whenever the event source is
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dispatched more often than the specified burst within the specified interval it is placed in a mode
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similar to being disabled with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and the <constant>SD_EVENT_OFF</constant> parameter. However it is disabled only temporarily – once the
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specified interval is over regular operation resumes. It is again disabled temporarily once the specified rate
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limiting is hit the next time. If either the interval or the burst value are specified as zero, rate
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limiting is turned off. By default event sources do not have rate limiting enabled. Note that rate
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limiting and disabling via <function>sd_event_source_set_enabled()</function> are independent of each
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other, and an event source will only effect event loop wake-ups and is dispatched while it both is
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enabled and rate limiting is not in effect.</para>
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<para><function>sd_event_source_get_ratelimit()</function> may be used to query the current rate limiting
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parameters set on the event source object <parameter>source</parameter>. The previously set interval and
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burst vales are returned in the second and third argument.</para>
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<para><function>sd_event_source_is_ratelimited()</function> may be used to query whether the event source
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is currently affected by rate limiting, i.e. it has recently hit the rate limit and is currently
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temporarily disabled due to that.</para>
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<para>Rate limiting is currently implemented for I/O, timer, signal, defer and inotify event
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sources.</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_source_set_ratelimit()</function> and
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<function>sd_event_source_get_ratelimit()</function> return a non-negative integer. On failure, they
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return a negative errno-style error code. <function>sd_event_source_is_ratelimited</function> returns
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zero if rate limiting is currently not in effect and greater than zero if it is in effect; it returns a
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negative errno-style error code on failure.</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>-EINVAL</constant></term>
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<listitem><para><parameter>source</parameter> is not a valid pointer to an
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<structname>sd_event_source</structname> object.
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</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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<varlistentry>
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<term><constant>-EDOM</constant></term>
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<listitem><para>It was attempted to use the rate limiting feature on an event source type that does
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not support rate limiting.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOEXEC</constant></term>
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<listitem><para><function>sd_event_source_get_ratelimit()</function> was called on an event source
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that doesn't have rate limiting configured.</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>sd-event</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_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_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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