man/sd_bus_track_add_name.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_bus_track_add_name" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_bus_track_add_name</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_bus_track_add_name</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_bus_track_add_name</refname>
  23     <refname>sd_bus_track_add_sender</refname>
  24     <refname>sd_bus_track_remove_name</refname>
  25     <refname>sd_bus_track_remove_sender</refname>
  26     <refname>sd_bus_track_count</refname>
  27     <refname>sd_bus_track_count_sender</refname>
  28     <refname>sd_bus_track_count_name</refname>
  29     <refname>sd_bus_track_contains</refname>
  30     <refname>sd_bus_track_first</refname>
  31     <refname>sd_bus_track_next</refname>
  32
  33     <refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose>
  34   </refnamediv>
  35
  36   <refsynopsisdiv>
  37     <funcsynopsis>
  38       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  39
  40       <funcprototype>
  41         <funcdef>int <function>sd_bus_track_add_name</function></funcdef>
  42         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  43         <paramdef>const char* <parameter>name</parameter></paramdef>
  44       </funcprototype>
  45
  46       <funcprototype>
  47         <funcdef>int <function>sd_bus_track_add_sender</function></funcdef>
  48         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  49         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_bus_track_remove_name</function></funcdef>
  54         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  55         <paramdef>const char* <parameter>name</parameter></paramdef>
  56       </funcprototype>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_bus_track_remove_sender</function></funcdef>
  60         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  61         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
  62       </funcprototype>
  63
  64       <funcprototype>
  65         <funcdef>unsigned <function>sd_bus_track_count</function></funcdef>
  66         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef>int <function>sd_bus_track_count_name</function></funcdef>
  71         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  72         <paramdef>const char* <parameter>name</parameter></paramdef>
  73       </funcprototype>
  74
  75       <funcprototype>
  76         <funcdef>int <function>sd_bus_track_count_sender</function></funcdef>
  77         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  78         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
  79       </funcprototype>
  80
  81       <funcprototype>
  82         <funcdef>int <function>sd_bus_track_contains</function></funcdef>
  83         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  84         <paramdef>const char* <parameter>name</parameter></paramdef>
  85       </funcprototype>
  86
  87       <funcprototype>
  88         <funcdef>const char* <function>sd_bus_track_first</function></funcdef>
  89         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  90       </funcprototype>
  91
  92       <funcprototype>
  93         <funcdef>const char* <function>sd_bus_track_next</function></funcdef>
  94         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  95       </funcprototype>
  96
  97     </funcsynopsis>
  98   </refsynopsisdiv>
  99
 100   <refsect1>
 101     <title>Description</title>
 102
 103     <para><function>sd_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first
 104     argument should refer to a bus peer tracking object created with
 105     <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second
 106     name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not
 107     tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode
 108     is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by
 109     one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many
 110     times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use
 111     <citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
 112     switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as
 113     it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects
 114     may track the same name.</para>
 115
 116     <para><function>sd_bus_track_remove_name()</function> undoes the effect of
 117     <function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending
 118     on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove
 119     the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name
 120     only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly
 121     remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para>
 122
 123     <para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are
 124     similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but
 125     take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer
 126     tracking object. As messages always originate from unique names, and never from well-known names this means that
 127     this call will effectively only add unique names to the bus peer tracking object.</para>
 128
 129     <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the
 130     specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and
 131     hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only
 132     counted as one, regardless if recursive mode is used or not.</para>
 133
 134     <para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified
 135     name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been
 136     added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be
 137     returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same
 138     name.</para>
 139
 140     <para><function>sd_bus_track_count_sender()</function> is similar to
 141     <function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter
 142     matching the sender of the message.</para>
 143
 144     <para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been
 145     added at least once to the specified bus peer tracking object.</para>
 146
 147     <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to
 148     enumerate all names currently being tracked by the passed bus peer tracking
 149     object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally
 150     maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name
 151     contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been
 152     added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant>
 153     immediately. The order in which names are returned is undefined; in particular which name is considered the first
 154     returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus
 155     peer tracking object it is only returned once by this enumeration. If new names are added to or existing names
 156     removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation
 157     of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</para>
 158   </refsect1>
 159
 160   <refsect1>
 161     <title>Return Value</title>
 162
 163     <para>On success, <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function>
 164     return 0 if the specified name has already been added to the bus peer tracking object before and positive if it
 165     hasn't. On failure, they return a negative errno-style error code.</para>
 166
 167     <para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return
 168     positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In
 169     non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode
 170     <constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error
 171     code.</para>
 172
 173     <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on
 174     failure.</para>
 175
 176     <para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return
 177     the current per-name counter for the specified name or the sender of the specified message. Zero is returned for
 178     names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only
 179     returned in recursive mode. On failure, a negative errno-style error code is returned.</para>
 180
 181     <para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking
 182     object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para>
 183
 184     <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next
 185     name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is
 186     reached and on error.</para>
 187   </refsect1>
 188
 189   <refsect1>
 190     <title>Errors</title>
 191
 192     <para>Returned errors may indicate the following problems:</para>
 193
 194     <variablelist>
 195
 196       <varlistentry>
 197         <term><constant>-EUNATCH</constant></term>
 198
 199         <listitem><para><function>sd_bus_track_remove_name()</function> or
 200         <function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added to the bus
 201         peer object.</para></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term><constant>-EINVAL</constant></term>
 206
 207         <listitem><para>Specified parameter is invalid.</para></listitem>
 208       </varlistentry>
 209
 210       <varlistentry>
 211         <term><constant>-ENOMEM</constant></term>
 212
 213         <listitem><para>Memory allocation failed.</para></listitem>
 214       </varlistentry>
 215
 216     </variablelist>
 217   </refsect1>
 218
 219   <xi:include href="libsystemd-pkgconfig.xml" />
 220
 221   <refsect1>
 222     <title>See Also</title>
 223
 224     <para>
 225       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 226       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 227       <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 228     </para>
 229   </refsect1>
 230
 231 </refentry>