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229 lines
12 KiB
XML
229 lines
12 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_bus_track_add_name" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_track_add_name</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_track_add_name</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_track_add_name</refname>
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<refname>sd_bus_track_add_sender</refname>
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<refname>sd_bus_track_remove_name</refname>
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<refname>sd_bus_track_remove_sender</refname>
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<refname>sd_bus_track_count</refname>
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<refname>sd_bus_track_count_sender</refname>
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<refname>sd_bus_track_count_name</refname>
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<refname>sd_bus_track_contains</refname>
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<refname>sd_bus_track_first</refname>
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<refname>sd_bus_track_next</refname>
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<refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_add_name</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>const char* <parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_add_sender</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_remove_name</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>const char* <parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_remove_sender</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>unsigned <function>sd_bus_track_count</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_count_name</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>const char* <parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_count_sender</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_contains</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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<paramdef>const char* <parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>const char* <function>sd_bus_track_first</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>const char* <function>sd_bus_track_next</function></funcdef>
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<paramdef>sd_bus_track* <parameter>t</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_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first
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argument should refer to a bus peer tracking object created with
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<citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second
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name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not
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tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode
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is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by
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one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many
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times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use
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<citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
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switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as
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it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects
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may track the same name.</para>
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<para><function>sd_bus_track_remove_name()</function> undoes the effect of
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<function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending
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on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove
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the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name
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only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly
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remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para>
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<para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are
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similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but
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take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer
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tracking object. As messages always originate from unique names, and never from well-known names this means that
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this call will effectively only add unique names to the bus peer tracking object.</para>
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<para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the
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specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and
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hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only
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counted as one, regardless if recursive mode is used or not.</para>
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<para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified
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name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been
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added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be
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returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same
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name.</para>
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<para><function>sd_bus_track_count_sender()</function> is similar to
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<function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter
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matching the sender of the message.</para>
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<para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been
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added at least once to the specified bus peer tracking object.</para>
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<para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to
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enumerate all names currently being tracked by the passed bus peer tracking
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object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally
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maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name
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contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been
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added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant>
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immediately. The order in which names are returned is undefined; in particular which name is considered the first
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returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus
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peer tracking object it is only returned once by this enumeration. If new names are added to or existing names
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removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation
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of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</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_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function>
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return 0 if the specified name has already been added to the bus peer tracking object before and positive if it
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hasn't. On failure, they return a negative errno-style error code.</para>
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<para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return
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positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In
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non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode
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<constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error
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code.</para>
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<para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on
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failure.</para>
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<para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return
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the current per-name counter for the specified name or the sender of the specified message. Zero is returned for
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names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only
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returned in recursive mode. On failure, a negative errno-style error code is returned.</para>
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<para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking
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object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para>
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<para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next
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name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is
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reached and on error.</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>-EUNATCH</constant></term>
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<listitem><para><function>sd_bus_track_remove_name()</function> or
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<function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added
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to the bus peer 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>Specified parameter is invalid.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</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-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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