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f47781d8 | 1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
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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 | <!-- | |
e3bff60a | 6 | This file is part of systemd. |
60f067b4 | 7 | |
e3bff60a | 8 | Copyright 2014 Zbigniew Jędrzejewski-Szmek |
60f067b4 | 9 | |
e3bff60a MP |
10 | systemd is free software; you can redistribute it and/or modify it |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
60f067b4 | 14 | |
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15 | systemd is distributed in the hope that it will be useful, but |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
60f067b4 | 19 | |
e3bff60a MP |
20 | You should have received a copy of the GNU Lesser General Public License |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
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22 | --> |
23 | ||
86f210e9 | 24 | <refentry id="sd_bus_default"> |
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25 | |
26 | <refentryinfo> | |
e3bff60a | 27 | <title>sd_bus_default</title> |
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28 | <productname>systemd</productname> |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>A monkey with a typewriter</contrib> | |
33 | <firstname>Zbigniew</firstname> | |
34 | <surname>Jędrzejewski-Szmek</surname> | |
35 | <email>zbyszek@in.waw.pl</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
e3bff60a | 41 | <refentrytitle>sd_bus_default</refentrytitle> |
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42 | <manvolnum>3</manvolnum> |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
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46 | <refname>sd_bus_default</refname> |
47 | <refname>sd_bus_default_user</refname> | |
48 | <refname>sd_bus_default_system</refname> | |
49 | ||
50 | <refname>sd_bus_open</refname> | |
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51 | <refname>sd_bus_open_user</refname> |
52 | <refname>sd_bus_open_system</refname> | |
53 | <refname>sd_bus_open_system_remote</refname> | |
e3bff60a | 54 | <refname>sd_bus_open_system_machine</refname> |
60f067b4 | 55 | |
e3bff60a | 56 | <refpurpose>Acquire a connection to a system or user bus</refpurpose> |
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57 | </refnamediv> |
58 | ||
59 | <refsynopsisdiv> | |
60 | <funcsynopsis> | |
61 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
62 | ||
63 | <funcprototype> | |
e3bff60a | 64 | <funcdef>int <function>sd_bus_default</function></funcdef> |
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65 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
66 | </funcprototype> | |
67 | ||
68 | <funcprototype> | |
e3bff60a | 69 | <funcdef>int <function>sd_bus_default_user</function></funcdef> |
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70 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
71 | </funcprototype> | |
72 | ||
73 | <funcprototype> | |
e3bff60a | 74 | <funcdef>int <function>sd_bus_default_system</function></funcdef> |
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75 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
76 | </funcprototype> | |
77 | ||
78 | <funcprototype> | |
e3bff60a | 79 | <funcdef>int <function>sd_bus_open</function></funcdef> |
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80 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
81 | </funcprototype> | |
82 | ||
83 | <funcprototype> | |
e3bff60a | 84 | <funcdef>int <function>sd_bus_open_user</function></funcdef> |
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85 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
86 | </funcprototype> | |
87 | ||
88 | <funcprototype> | |
e3bff60a | 89 | <funcdef>int <function>sd_bus_open_system</function></funcdef> |
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90 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
91 | </funcprototype> | |
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92 | |
93 | <funcprototype> | |
94 | <funcdef>int <function>sd_bus_open_system_remote</function></funcdef> | |
95 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> | |
96 | <paramdef>const char *<parameter>host</parameter></paramdef> | |
97 | </funcprototype> | |
98 | ||
99 | <funcprototype> | |
100 | <funcdef>int <function>sd_bus_open_system_machine</function></funcdef> | |
101 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> | |
102 | <paramdef>const char *<parameter>machine</parameter></paramdef> | |
103 | </funcprototype> | |
104 | ||
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105 | </funcsynopsis> |
106 | </refsynopsisdiv> | |
107 | ||
108 | <refsect1> | |
109 | <title>Description</title> | |
110 | ||
e3bff60a | 111 | <para><function>sd_bus_default()</function> acquires a bus |
fb183854 | 112 | connection object to the user bus when invoked in user context, or |
e3bff60a | 113 | to the system bus otherwise. The connection object is associated |
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114 | with the calling thread. Each time the function is invoked from |
115 | the same thread the same object is returned, but its reference | |
116 | count is increased by one, as long as at least one reference is | |
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117 | kept. When the last reference to the connection is dropped (using |
118 | the | |
119 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
120 | call), the connection is terminated. Note that the connection is | |
121 | not automatically terminated when the associated thread ends. It | |
122 | is important to drop the last reference to the bus connection | |
123 | explicitly before the thread ends or otherwise the connection will | |
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124 | be leaked. Also, queued but unread or unwritten messages keep the |
125 | bus referenced, see below.</para> | |
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126 | |
127 | <para><function>sd_bus_default_user()</function> returns a user | |
7035cd9e | 128 | bus connection object associated with the calling thread. |
e3bff60a | 129 | <function>sd_bus_default_system()</function> is similar, but |
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130 | connects to the system bus. Note that |
131 | <function>sd_bus_default()</function> is identical to these two | |
132 | calls, depending on the execution context.</para> | |
60f067b4 | 133 | |
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134 | <para><function>sd_bus_open()</function> creates a new, |
135 | independent bus connection to the user bus when invoked in user | |
fb183854 | 136 | context, or the system bus |
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137 | otherwise. <function>sd_bus_open_user()</function> is similar, but |
138 | connects only to the user bus. | |
139 | <function>sd_bus_open_system()</function> does the same, but | |
140 | connects to the system bus. In contrast to | |
141 | <function>sd_bus_default()</function>, | |
142 | <function>sd_bus_default_user()</function>, | |
143 | <function>sd_bus_default_system()</function> these calls return | |
144 | new, independent connection objects that are not associated with | |
145 | the invoking thread and are not shared between multiple | |
146 | invocations. It is recommended to share connections per thread to | |
147 | efficiently make use the available resources. Thus, it is | |
148 | recommended to use <function>sd_bus_default()</function>, | |
149 | <function>sd_bus_default_user()</function>, | |
150 | <function>sd_bus_default_system()</function> to connect to the | |
151 | user or system buses.</para> | |
152 | ||
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153 | <para>If the <varname>$DBUS_SESSION_BUS_ADDRESS</varname> environment |
154 | variable is set | |
5eef597e | 155 | (cf. <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>), |
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156 | it will be used as the address of the user bus. This variable can |
157 | contain multiple addresses separated by <literal>;</literal>. If | |
158 | this variable is not set, a suitable default for the default user | |
159 | D-Bus instance will be used.</para> | |
160 | ||
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161 | <para>If the <varname>$DBUS_SYSTEM_BUS_ADDRESS</varname> |
162 | environment variable is set, it will be used as the address of the | |
163 | system bus. This variable uses the same syntax as | |
164 | <varname>$DBUS_SESSION_BUS_ADDRESS</varname>. If this variable is | |
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165 | not set, a suitable default for the default system D-Bus instance |
166 | will be used.</para> | |
167 | ||
168 | <para><function>sd_bus_open_system_remote()</function> connects to | |
169 | the system bus on the specified <parameter>host</parameter> using | |
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170 | <citerefentry |
171 | project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <parameter>host</parameter> | |
172 | consists of an optional user name followed by the | |
173 | <literal>@</literal> symbol, and the hostname. | |
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174 | </para> |
175 | ||
fb183854 | 176 | <para><function>sd_bus_open_system_machine()</function> connects |
f47781d8 | 177 | to the system bus in the specified <parameter>machine</parameter>, |
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178 | where <parameter>machine</parameter> is the name of a local |
179 | container. See | |
60f067b4 | 180 | <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
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181 | for more information about the "machine" concept. Note that |
182 | connections into local containers are only available to privileged | |
183 | processes at this time.</para> | |
184 | ||
185 | <para>These calls allocate a bus connection object and initiate | |
186 | the connection to a well-known bus of some form. An alternative to | |
187 | using these high-level calls is to create an unconnected bus | |
188 | object with | |
189 | <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
190 | and to connect it with | |
191 | <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
192 | </para> | |
60f067b4 | 193 | |
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194 | </refsect1> |
195 | ||
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196 | <refsect1> |
197 | <title>Reference ownership</title> | |
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198 | <para>The functions <function>sd_bus_open()</function>, |
199 | <function>sd_bus_open_user()</function>, | |
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200 | <function>sd_bus_open_system()</function>, |
201 | <function>sd_bus_open_system_remote()</function>, and | |
202 | <function>sd_bus_open_system_machine()</function> return a new | |
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203 | connection object and the caller owns the sole reference. When not |
204 | needed anymore, this reference should be destroyed with | |
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205 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
206 | </para> | |
207 | ||
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208 | <para>The functions <function>sd_bus_default()</function>, |
209 | <function>sd_bus_default_user()</function> and | |
210 | <function>sd_bus_default_system()</function> do not necessarily | |
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211 | create a new object, but increase the connection reference of an |
212 | existing connection object by one. Use | |
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213 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
214 | to drop the reference.</para> | |
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215 | |
216 | <para>Queued but unwritten/unread messages also keep a reference | |
217 | to their bus connection object. For this reason, even if an | |
218 | application dropped all references to a bus connection it might | |
219 | not get destroyed right-away. Until all incoming queued | |
220 | messages are read, and until all outgoing unwritten messages are | |
221 | written, the bus object will stay | |
222 | alive. <function>sd_bus_flush()</function> may be used to write | |
223 | all outgoing queued messages so they drop their references. To | |
224 | flush the unread incoming messages use | |
225 | <function>sd_bus_close()</function>, which will also close the bus | |
226 | connection. When using the default bus logic it is a good idea to | |
227 | first invoke <function>sd_bus_flush()</function> followed by | |
228 | <function>sd_bus_close()</function> when a thread or process | |
229 | terminates, and thus its bus connection object should be | |
230 | freed.</para> | |
231 | ||
232 | <para>The life-cycle of the default bus connection should be the | |
233 | responsibility of the code that creates/owns the thread the | |
234 | default bus connection object is associated with. Library code | |
235 | should neither call <function>sd_bus_flush()</function> nor | |
236 | <function>sd_bus_close()</function> on default bus objects unless | |
237 | it does so in its own private, self-allocated thread. Library code | |
238 | should not use the default bus object in other threads unless it | |
239 | is clear that the program using it will life-cycle the bus | |
240 | connection object and flush and close it before exiting from the | |
241 | thread. In libraries where it is not clear that the calling | |
242 | program will life-cycle the bus connection object it is hence | |
243 | recommended to use <function>sd_bus_open_system()</function> | |
244 | instead of <function>sd_bus_default_system()</function> and | |
245 | related calls.</para> | |
246 | </refsect1> | |
247 | ||
248 | <refsect1> | |
249 | <title>Return Value</title> | |
250 | ||
251 | <para>On success, these calls return 0 or a positive | |
252 | integer. On failure, these calls return a negative | |
253 | errno-style error code.</para> | |
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254 | </refsect1> |
255 | ||
256 | <refsect1> | |
257 | <title>Errors</title> | |
258 | ||
259 | <para>Returned errors may indicate the following problems:</para> | |
260 | ||
261 | <variablelist> | |
262 | ||
263 | <varlistentry> | |
5eef597e | 264 | <term><constant>-EINVAL</constant></term> |
60f067b4 | 265 | |
e3bff60a | 266 | <listitem><para>The specified parameters are invalid.</para></listitem> |
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267 | </varlistentry> |
268 | ||
269 | <varlistentry> | |
5eef597e | 270 | <term><constant>-ENOMEM</constant></term> |
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271 | |
272 | <listitem><para>Memory allocation failed.</para></listitem> | |
273 | </varlistentry> | |
274 | ||
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275 | <varlistentry> |
276 | <term><constant>-ESOCKTNOSUPPORT</constant></term> | |
277 | ||
278 | <listitem><para>The protocol version required to connect to the selected bus is not supported.</para></listitem> | |
279 | </varlistentry> | |
60f067b4 | 280 | </variablelist> |
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281 | |
282 | <para>In addition, any further connection-related errors may be | |
283 | by returned. See <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
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284 | </refsect1> |
285 | ||
286 | <refsect1> | |
287 | <title>Notes</title> | |
288 | ||
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289 | <para><function>sd_bus_open_user()</function> and the other |
290 | functions described here are available as a shared library, which | |
291 | can be compiled and linked to with the | |
292 | <constant>libsystemd</constant> <citerefentry | |
293 | project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
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294 | file.</para> |
295 | </refsect1> | |
296 | ||
297 | <refsect1> | |
298 | <title>See Also</title> | |
299 | ||
300 | <para> | |
301 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
302 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
303 | <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
304 | <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
305 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
e3bff60a | 306 | <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
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307 | <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
308 | <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
309 | </para> | |
310 | </refsect1> | |
311 | ||
312 | </refentry> |