1<?xml version='1.0'?> 2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> 5 6<refentry id="sd_bus_track_add_name" xmlns:xi="http://www.w3.org/2001/XInclude"> 7 8 <refentryinfo> 9 <title>sd_bus_track_add_name</title> 10 <productname>systemd</productname> 11 </refentryinfo> 12 13 <refmeta> 14 <refentrytitle>sd_bus_track_add_name</refentrytitle> 15 <manvolnum>3</manvolnum> 16 </refmeta> 17 18 <refnamediv> 19 <refname>sd_bus_track_add_name</refname> 20 <refname>sd_bus_track_add_sender</refname> 21 <refname>sd_bus_track_remove_name</refname> 22 <refname>sd_bus_track_remove_sender</refname> 23 <refname>sd_bus_track_count</refname> 24 <refname>sd_bus_track_count_sender</refname> 25 <refname>sd_bus_track_count_name</refname> 26 <refname>sd_bus_track_contains</refname> 27 <refname>sd_bus_track_first</refname> 28 <refname>sd_bus_track_next</refname> 29 30 <refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose> 31 </refnamediv> 32 33 <refsynopsisdiv> 34 <funcsynopsis> 35 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> 36 37 <funcprototype> 38 <funcdef>int <function>sd_bus_track_add_name</function></funcdef> 39 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 40 <paramdef>const char* <parameter>name</parameter></paramdef> 41 </funcprototype> 42 43 <funcprototype> 44 <funcdef>int <function>sd_bus_track_add_sender</function></funcdef> 45 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 46 <paramdef>sd_bus_message* <parameter>message</parameter></paramdef> 47 </funcprototype> 48 49 <funcprototype> 50 <funcdef>int <function>sd_bus_track_remove_name</function></funcdef> 51 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 52 <paramdef>const char* <parameter>name</parameter></paramdef> 53 </funcprototype> 54 55 <funcprototype> 56 <funcdef>int <function>sd_bus_track_remove_sender</function></funcdef> 57 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 58 <paramdef>sd_bus_message* <parameter>message</parameter></paramdef> 59 </funcprototype> 60 61 <funcprototype> 62 <funcdef>unsigned <function>sd_bus_track_count</function></funcdef> 63 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 64 </funcprototype> 65 66 <funcprototype> 67 <funcdef>int <function>sd_bus_track_count_name</function></funcdef> 68 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 69 <paramdef>const char* <parameter>name</parameter></paramdef> 70 </funcprototype> 71 72 <funcprototype> 73 <funcdef>int <function>sd_bus_track_count_sender</function></funcdef> 74 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 75 <paramdef>sd_bus_message* <parameter>message</parameter></paramdef> 76 </funcprototype> 77 78 <funcprototype> 79 <funcdef>int <function>sd_bus_track_contains</function></funcdef> 80 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 81 <paramdef>const char* <parameter>name</parameter></paramdef> 82 </funcprototype> 83 84 <funcprototype> 85 <funcdef>const char* <function>sd_bus_track_first</function></funcdef> 86 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 87 </funcprototype> 88 89 <funcprototype> 90 <funcdef>const char* <function>sd_bus_track_next</function></funcdef> 91 <paramdef>sd_bus_track* <parameter>t</parameter></paramdef> 92 </funcprototype> 93 94 </funcsynopsis> 95 </refsynopsisdiv> 96 97 <refsect1> 98 <title>Description</title> 99 100 <para><function>sd_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first 101 argument should refer to a bus peer tracking object created with 102 <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second 103 name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not 104 tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode 105 is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by 106 one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many 107 times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use 108 <citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to 109 switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as 110 it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects 111 may track the same name.</para> 112 113 <para><function>sd_bus_track_remove_name()</function> undoes the effect of 114 <function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending 115 on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove 116 the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name 117 only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly 118 remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para> 119 120 <para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are 121 similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but 122 take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer 123 tracking object. As messages always originate from unique names, and never from well-known names this means that 124 this call will effectively only add unique names to the bus peer tracking object.</para> 125 126 <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the 127 specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and 128 hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only 129 counted as one, regardless if recursive mode is used or not.</para> 130 131 <para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified 132 name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been 133 added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be 134 returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same 135 name.</para> 136 137 <para><function>sd_bus_track_count_sender()</function> is similar to 138 <function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter 139 matching the sender of the message.</para> 140 141 <para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been 142 added at least once to the specified bus peer tracking object.</para> 143 144 <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to 145 enumerate all names currently being tracked by the passed bus peer tracking 146 object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally 147 maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name 148 contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been 149 added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant> 150 immediately. The order in which names are returned is undefined; in particular which name is considered the first 151 returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus 152 peer tracking object it is only returned once by this enumeration. If new names are added to or existing names 153 removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation 154 of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</para> 155 </refsect1> 156 157 <refsect1> 158 <title>Return Value</title> 159 160 <para>On success, <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function> 161 return 0 if the specified name has already been added to the bus peer tracking object before and positive if it 162 hasn't. On failure, they return a negative errno-style error code.</para> 163 164 <para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return 165 positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In 166 non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode 167 <constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error 168 code.</para> 169 170 <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on 171 failure.</para> 172 173 <para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return 174 the current per-name counter for the specified name or the sender of the specified message. Zero is returned for 175 names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only 176 returned in recursive mode. On failure, a negative errno-style error code is returned.</para> 177 178 <para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking 179 object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para> 180 181 <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next 182 name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is 183 reached and on error.</para> 184 185 <refsect2> 186 <title>Errors</title> 187 188 <para>Returned errors may indicate the following problems:</para> 189 190 <variablelist> 191 192 <varlistentry> 193 <term><constant>-EUNATCH</constant></term> 194 195 <listitem><para><function>sd_bus_track_remove_name()</function> or 196 <function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added 197 to the bus peer object.</para></listitem> 198 </varlistentry> 199 200 <varlistentry> 201 <term><constant>-EINVAL</constant></term> 202 203 <listitem><para>Specified parameter is invalid.</para></listitem> 204 </varlistentry> 205 206 <varlistentry> 207 <term><constant>-ENOMEM</constant></term> 208 209 <listitem><para>Memory allocation failed.</para></listitem> 210 </varlistentry> 211 212 </variablelist> 213 </refsect2> 214 </refsect1> 215 216 <xi:include href="libsystemd-pkgconfig.xml" /> 217 218 <refsect1> 219 <title>See Also</title> 220 221 <para> 222 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 223 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 224 <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> 225 </para> 226 </refsect1> 227 228</refentry> 229