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1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
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 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
ecddb2b5 LP |
8 | This file is part of systemd. |
9 | ||
10 | Copyright 2016 Lennart Poettering | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="sd_bus_track_new"> | |
27 | ||
28 | <refentryinfo> | |
29 | <title>sd_bus_track_new</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Lennart</firstname> | |
36 | <surname>Poettering</surname> | |
37 | <email>lennart@poettering.net</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd_bus_track_new</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd_bus_track_new</refname> | |
49 | <refname>sd_bus_track_ref</refname> | |
50 | <refname>sd_bus_track_unref</refname> | |
51 | <refname>sd_bus_track_unrefp</refname> | |
52 | <refname>sd_bus_track_set_recursive</refname> | |
53 | <refname>sd_bus_track_get_recursive</refname> | |
54 | <refname>sd_bus_track_get_bus</refname> | |
55 | <refname>sd_bus_track_get_userdata</refname> | |
56 | <refname>sd_bus_track_set_userdata</refname> | |
57 | ||
58 | <refpurpose>Track bus peers</refpurpose> | |
59 | </refnamediv> | |
60 | ||
61 | <refsynopsisdiv> | |
62 | <funcsynopsis> | |
63 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
64 | ||
65 | <funcprototype> | |
66 | <funcdef>int <function>sd_bus_track_new</function></funcdef> | |
67 | <paramdef>sd_bus* <parameter>bus</parameter></paramdef> | |
68 | <paramdef>sd_bus_track** <parameter>ret</parameter></paramdef> | |
69 | <paramdef>sd_bus_track_handler_t <parameter>handler</parameter></paramdef> | |
70 | <paramdef>void* <parameter>userdata</parameter></paramdef> | |
71 | </funcprototype> | |
72 | ||
73 | <funcprototype> | |
74 | <funcdef>sd_bus_track *<function>sd_bus_track_ref</function></funcdef> | |
75 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
76 | </funcprototype> | |
77 | ||
78 | <funcprototype> | |
79 | <funcdef>sd_bus_track *<function>sd_bus_track_unref</function></funcdef> | |
80 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
81 | </funcprototype> | |
82 | ||
83 | <funcprototype> | |
84 | <funcdef>void <function>sd_bus_track_unrefp</function></funcdef> | |
85 | <paramdef>sd_bus_track **<parameter>t</parameter></paramdef> | |
86 | </funcprototype> | |
87 | ||
88 | <funcprototype> | |
89 | <funcdef>int <function>sd_bus_track_get_recursive</function></funcdef> | |
90 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
91 | </funcprototype> | |
92 | ||
93 | <funcprototype> | |
94 | <funcdef>int <function>sd_bus_track_set_recursive</function></funcdef> | |
95 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
96 | <paramdef>int <parameter>b</parameter></paramdef> | |
97 | </funcprototype> | |
98 | ||
99 | <funcprototype> | |
100 | <funcdef>sd_bus* <function>sd_bus_track_get_bus</function></funcdef> | |
101 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
102 | </funcprototype> | |
103 | ||
104 | <funcprototype> | |
105 | <funcdef>void* <function>sd_bus_track_get_userdata</function></funcdef> | |
106 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
107 | </funcprototype> | |
108 | ||
109 | <funcprototype> | |
110 | <funcdef>void* <function>sd_bus_track_set_userdata</function></funcdef> | |
111 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
112 | <paramdef>void *userdata</paramdef> | |
113 | </funcprototype> | |
114 | ||
115 | </funcsynopsis> | |
116 | </refsynopsisdiv> | |
117 | ||
118 | <refsect1> | |
119 | <title>Description</title> | |
120 | ||
121 | <para><function>sd_bus_track_new()</function> creates a new bus peer tracking object. The object is allocated for | |
122 | the specified bus, and returned in the <parameter>*ret</parameter> parameter. After use, the object should be freed | |
123 | again by dropping the acquired reference with <function>sd_bus_track_unref()</function> (see below). A bus peer | |
124 | tracking object may be used to keep track of peers on a specific IPC bus, for cases where peers are making use of | |
125 | one or more local objects, in order to control the lifecycle of the local objects and ensure they stay around as | |
126 | long as the peers needing them are around, and unreferenced (and possibly destroyed) as soon as all relevant peers | |
127 | have vanished. Each bus peer tracking object may be used to track zero, one or more peers add a time. References to | |
128 | specific bus peers are added via | |
129 | <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> or | |
130 | <function>sd_bus_track_add_sender()</function>. They may be dropped again via | |
131 | <function>sd_bus_track_remove_name()</function> and | |
132 | <function>sd_bus_track_remove_sender()</function>. Alternatively, references on peers are removed automatically | |
133 | when they disconnect from the bus. If non-NULL the <parameter>handler</parameter> may specify a function that is | |
134 | invoked whenever the last reference is dropped, regardless whether the reference is dropped explicitly via | |
135 | <function>sd_bus_track_remove_name()</function> or implicitly because the peer disconnected from the bus. The final | |
136 | argument <parameter>userdata</parameter> may be used to attach a generic user data pointer to the object. This | |
137 | pointer is passed to the handler callback when it is invoked.</para> | |
138 | ||
139 | <para><function>sd_bus_track_ref()</function> creates a new reference to a bus peer tracking object. This object | |
140 | will not be destroyed until <function>sd_bus_track_unref()</function> has been called as many times plus once | |
141 | more. Once the reference count has dropped to zero, the specified object cannot be used anymore, further calls to | |
142 | <function>sd_bus_track_ref()</function> or <function>sd_bus_track_unref()</function> on the same object are | |
143 | illegal.</para> | |
144 | ||
145 | <para><function>sd_bus_track_unref()</function> destroys a reference to a bus peer tracking object.</para> | |
146 | ||
147 | <para><function>sd_bus_track_unrefp()</function> is similar to <function>sd_bus_track_unref()</function> but takes | |
148 | a pointer to a pointer to an <type>sd_bus_track</type> object. This call is useful in conjunction with GCC's and | |
149 | LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable | |
150 | Attribute</ulink>. Note that this function is defined as inline function.</para> | |
151 | ||
152 | <para><function>sd_bus_track_ref()</function>, <function>sd_bus_track_unref()</function> and | |
153 | <function>sd_bus_track_unrefp()</function> execute no operation if the passed in bus peer tracking object is | |
154 | <constant>NULL</constant>.</para> | |
155 | ||
156 | <para>Bus peer tracking objects may exist in two modes: by default they operate in non-recursive mode, but may | |
157 | optionally be switched into recursive mode. If operating in the default non-recursive mode a peer is either tracked | |
158 | or not tracked. In this mode invoking <function>sd_bus_track_add_name()</function> multiple times in a row for the | |
159 | same peer is fully equivalent to calling it just once, as the call adds the peer to the set of tracked peers if | |
160 | necessary, and executes no operation if the peer is already being tracked. A single invocation of | |
161 | <function>sd_bus_track_remove_name()</function> removes the reference on the peer again, regardless how many times | |
162 | <function>sd_bus_track_add_name()</function> was called before. If operating in recursive mode, the number of times | |
163 | <function>sd_bus_track_add_name()</function> is invoked for the same peer name is counted and | |
164 | <function>sd_bus_track_remove_name()</function> must be called the same number of times before the peer is not | |
165 | tracked anymore, with the exception when the tracked peer vanishes from the bus, in which case the count is | |
166 | irrelevant and the tracking of the specific peer is immediately | |
167 | removed. <function>sd_bus_track_get_recursive()</function> may be used to determine whether the bus peer tracking | |
168 | object is operating in recursive mode. <function>sd_bus_track_set_recursive()</function> may be used to enable or | |
169 | disable recursive mode. By default a bus peer tracking object operates in non-recursive mode, and | |
170 | <function>sd_bus_track_get_recursive()</function> for a newly allocated object hence returns a value equal to | |
171 | zero. Use <function>sd_bus_track_set_recursive()</function> to enable recursive mode, right after allocation. It | |
172 | takes a boolean argument to enable or disable recursive mode. Note that tracking objects for which | |
173 | <function>sd_bus_track_add_name()</function> was already invoked at least once (and which hence track already one | |
174 | or more peers) may not be switched from recursive to non-recursive mode anymore.</para> | |
175 | ||
176 | <para><function>sd_bus_track_get_bus()</function> returns the bus object the bus peer tracking object belongs | |
177 | to. It returns the bus object initially passed to <function>sd_bus_track_new()</function> when the object was | |
178 | allocated.</para> | |
179 | ||
180 | <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer set on the bus peer | |
181 | tracking object at the time of creation using <function>sd_bus_track_new()</function> or at a later time, using | |
182 | <function>sd_bus_track_set_userdata()</function>.</para> | |
183 | </refsect1> | |
184 | ||
185 | <refsect1> | |
186 | <title>Return Value</title> | |
187 | ||
188 | <para>On success, <function>sd_bus_track_new()</function> and <function>sd_bus_track_set_recursive()</function> | |
189 | return 0 or a positive integer. On failure, they return a negative errno-style error code.</para> | |
190 | ||
191 | <para><function>sd_bus_track_ref()</function> always returns the argument.</para> | |
192 | ||
193 | <para><function>sd_bus_track_unref()</function> always returns <constant>NULL</constant>.</para> | |
194 | ||
195 | <para><function>sd_bus_track_get_recursive()</function> returns 0 if non-recursive mode is selected (default), and | |
196 | greater than 0 if recursive mode is selected. On failure a negative errno-style error code is returned.</para> | |
197 | ||
198 | <para><function>sd_bus_track_get_bus()</function> returns the bus object associated to the bus peer tracking | |
199 | object.</para> | |
200 | ||
201 | <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer associated with the | |
202 | bus peer tracking object. <function>sd_bus_track_set_userdata()</function> returns the previous user data pointer | |
203 | set.</para> | |
204 | ||
205 | </refsect1> | |
206 | ||
207 | <refsect1> | |
208 | <title>Reference ownership</title> | |
209 | ||
210 | <para>The <function>sd_bus_track_new()</function> function creates a new object and the caller owns the sole | |
211 | reference. When not needed anymore, this reference should be destroyed with | |
212 | <function>sd_bus_track_unref()</function>. | |
213 | </para> | |
214 | </refsect1> | |
215 | ||
216 | <refsect1> | |
217 | <title>Errors</title> | |
218 | ||
219 | <para>Returned errors may indicate the following problems:</para> | |
220 | ||
221 | <variablelist> | |
222 | ||
223 | <varlistentry> | |
224 | <term><constant>-EBUSY</constant></term> | |
225 | ||
226 | <listitem><para>Bus peers have already been added to the bus peer tracking object and | |
227 | <function>sd_bus_track_set_recursive()</function> was called to change tracking mode.</para></listitem> | |
228 | </varlistentry> | |
229 | ||
230 | <varlistentry> | |
231 | <term><constant>-EINVAL</constant></term> | |
232 | ||
233 | <listitem><para>Specified parameter is invalid | |
234 | (<constant>NULL</constant> in case of output | |
235 | parameters).</para></listitem> | |
236 | </varlistentry> | |
237 | ||
238 | <varlistentry> | |
239 | <term><constant>-ENOMEM</constant></term> | |
240 | ||
241 | <listitem><para>Memory allocation failed.</para></listitem> | |
242 | </varlistentry> | |
243 | ||
244 | </variablelist> | |
245 | </refsect1> | |
246 | ||
247 | <refsect1> | |
248 | <title>Notes</title> | |
249 | ||
250 | <para><function>sd_bus_track_new()</function> and the other calls described here are available as a shared library, | |
251 | which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry | |
252 | project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> | |
253 | </refsect1> | |
254 | ||
255 | <refsect1> | |
256 | <title>See Also</title> | |
257 | ||
258 | <para> | |
259 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
260 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
261 | <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
262 | </para> | |
263 | </refsect1> | |
264 | ||
265 | </refentry> |