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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_bus_track_add_name" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_bus_track_add_name</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_bus_track_add_name</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_bus_track_add_name</refname>
+ <refname>sd_bus_track_add_sender</refname>
+ <refname>sd_bus_track_remove_name</refname>
+ <refname>sd_bus_track_remove_sender</refname>
+ <refname>sd_bus_track_count</refname>
+ <refname>sd_bus_track_count_sender</refname>
+ <refname>sd_bus_track_count_name</refname>
+ <refname>sd_bus_track_contains</refname>
+ <refname>sd_bus_track_first</refname>
+ <refname>sd_bus_track_next</refname>
+
+ <refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_add_name</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>const char* <parameter>name</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_add_sender</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_remove_name</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>const char* <parameter>name</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_remove_sender</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>unsigned <function>sd_bus_track_count</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_count_name</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>const char* <parameter>name</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_count_sender</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_contains</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ <paramdef>const char* <parameter>name</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>const char* <function>sd_bus_track_first</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>const char* <function>sd_bus_track_next</function></funcdef>
+ <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first
+ argument should refer to a bus peer tracking object created with
+ <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second
+ name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not
+ tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode
+ is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by
+ one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many
+ times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use
+ <citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
+ switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as
+ it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects
+ may track the same name.</para>
+
+ <para><function>sd_bus_track_remove_name()</function> undoes the effect of
+ <function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending
+ on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove
+ the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name
+ only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly
+ remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para>
+
+ <para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are
+ similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but
+ take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer
+ tracking object. As messages always originate from unique names, and never from well-known names this means that
+ this call will effectively only add unique names to the bus peer tracking object.</para>
+
+ <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the
+ specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and
+ hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only
+ counted as one, regardless if recursive mode is used or not.</para>
+
+ <para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified
+ name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been
+ added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be
+ returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same
+ name.</para>
+
+ <para><function>sd_bus_track_count_sender()</function> is similar to
+ <function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter
+ matching the sender of the message.</para>
+
+ <para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been
+ added at least once to the specified bus peer tracking object.</para>
+
+ <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to
+ enumerate all names currently being tracked by the passed bus peer tracking
+ object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally
+ maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name
+ contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been
+ added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant>
+ immediately. The order in which names are returned is undefined; in particular which name is considered the first
+ returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus
+ peer tracking object it is only returned once by this enumeration. If new names are added to or existing names
+ removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation
+ of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On success, <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function>
+ return 0 if the specified name has already been added to the bus peer tracking object before and positive if it
+ hasn't. On failure, they return a negative errno-style error code.</para>
+
+ <para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return
+ positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In
+ non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode
+ <constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error
+ code.</para>
+
+ <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on
+ failure.</para>
+
+ <para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return
+ the current per-name counter for the specified name or the sender of the specified message. Zero is returned for
+ names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only
+ returned in recursive mode. On failure, a negative errno-style error code is returned.</para>
+
+ <para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking
+ object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para>
+
+ <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next
+ name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is
+ reached and on error.</para>
+
+ <refsect2>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><constant>-EUNATCH</constant></term>
+
+ <listitem><para><function>sd_bus_track_remove_name()</function> or
+ <function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added
+ to the bus peer object.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para>Specified parameter is invalid.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOMEM</constant></term>
+
+ <listitem><para>Memory allocation failed.</para></listitem>
+ </varlistentry>
+
+ </variablelist>
+ </refsect2>
+ </refsect1>
+
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>