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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 | <!-- | |
52ad194e MB |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
e3bff60a | 8 | This file is part of systemd. |
60f067b4 | 9 | |
e3bff60a | 10 | Copyright 2014 Zbigniew Jędrzejewski-Szmek |
60f067b4 | 11 | |
e3bff60a MP |
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. | |
60f067b4 | 16 | |
e3bff60a MP |
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. | |
60f067b4 | 21 | |
e3bff60a MP |
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/>. | |
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24 | --> |
25 | ||
86f210e9 | 26 | <refentry id="sd_bus_default"> |
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27 | |
28 | <refentryinfo> | |
e3bff60a | 29 | <title>sd_bus_default</title> |
60f067b4 JS |
30 | <productname>systemd</productname> |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>A monkey with a typewriter</contrib> | |
35 | <firstname>Zbigniew</firstname> | |
36 | <surname>Jędrzejewski-Szmek</surname> | |
37 | <email>zbyszek@in.waw.pl</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
e3bff60a | 43 | <refentrytitle>sd_bus_default</refentrytitle> |
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44 | <manvolnum>3</manvolnum> |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
e3bff60a MP |
48 | <refname>sd_bus_default</refname> |
49 | <refname>sd_bus_default_user</refname> | |
50 | <refname>sd_bus_default_system</refname> | |
51 | ||
52 | <refname>sd_bus_open</refname> | |
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53 | <refname>sd_bus_open_user</refname> |
54 | <refname>sd_bus_open_system</refname> | |
55 | <refname>sd_bus_open_system_remote</refname> | |
e3bff60a | 56 | <refname>sd_bus_open_system_machine</refname> |
60f067b4 | 57 | |
e3bff60a | 58 | <refpurpose>Acquire a connection to a system or user bus</refpurpose> |
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59 | </refnamediv> |
60 | ||
61 | <refsynopsisdiv> | |
62 | <funcsynopsis> | |
63 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
64 | ||
65 | <funcprototype> | |
e3bff60a | 66 | <funcdef>int <function>sd_bus_default</function></funcdef> |
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67 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
68 | </funcprototype> | |
69 | ||
70 | <funcprototype> | |
e3bff60a | 71 | <funcdef>int <function>sd_bus_default_user</function></funcdef> |
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72 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
e3bff60a | 76 | <funcdef>int <function>sd_bus_default_system</function></funcdef> |
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77 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
78 | </funcprototype> | |
79 | ||
80 | <funcprototype> | |
e3bff60a | 81 | <funcdef>int <function>sd_bus_open</function></funcdef> |
60f067b4 JS |
82 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
83 | </funcprototype> | |
84 | ||
85 | <funcprototype> | |
e3bff60a | 86 | <funcdef>int <function>sd_bus_open_user</function></funcdef> |
60f067b4 JS |
87 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
88 | </funcprototype> | |
89 | ||
90 | <funcprototype> | |
e3bff60a | 91 | <funcdef>int <function>sd_bus_open_system</function></funcdef> |
60f067b4 JS |
92 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> |
93 | </funcprototype> | |
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94 | |
95 | <funcprototype> | |
96 | <funcdef>int <function>sd_bus_open_system_remote</function></funcdef> | |
97 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> | |
98 | <paramdef>const char *<parameter>host</parameter></paramdef> | |
99 | </funcprototype> | |
100 | ||
101 | <funcprototype> | |
102 | <funcdef>int <function>sd_bus_open_system_machine</function></funcdef> | |
103 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> | |
104 | <paramdef>const char *<parameter>machine</parameter></paramdef> | |
105 | </funcprototype> | |
106 | ||
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107 | </funcsynopsis> |
108 | </refsynopsisdiv> | |
109 | ||
110 | <refsect1> | |
111 | <title>Description</title> | |
112 | ||
e3bff60a | 113 | <para><function>sd_bus_default()</function> acquires a bus |
fb183854 | 114 | connection object to the user bus when invoked in user context, or |
e3bff60a | 115 | to the system bus otherwise. The connection object is associated |
7035cd9e | 116 | with the calling thread. Each time the function is invoked from |
db2df898 | 117 | the same thread, the same object is returned, but its reference |
7035cd9e | 118 | count is increased by one, as long as at least one reference is |
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119 | kept. When the last reference to the connection is dropped (using |
120 | the | |
121 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
122 | call), the connection is terminated. Note that the connection is | |
123 | not automatically terminated when the associated thread ends. It | |
124 | is important to drop the last reference to the bus connection | |
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125 | explicitly before the thread ends, as otherwise, the connection will |
126 | leak. Also, queued but unread or unwritten messages keep the | |
7035cd9e | 127 | bus referenced, see below.</para> |
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128 | |
129 | <para><function>sd_bus_default_user()</function> returns a user | |
7035cd9e | 130 | bus connection object associated with the calling thread. |
e3bff60a | 131 | <function>sd_bus_default_system()</function> is similar, but |
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132 | connects to the system bus. Note that |
133 | <function>sd_bus_default()</function> is identical to these two | |
134 | calls, depending on the execution context.</para> | |
60f067b4 | 135 | |
e3bff60a MP |
136 | <para><function>sd_bus_open()</function> creates a new, |
137 | independent bus connection to the user bus when invoked in user | |
fb183854 | 138 | context, or the system bus |
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139 | otherwise. <function>sd_bus_open_user()</function> is similar, but |
140 | connects only to the user bus. | |
141 | <function>sd_bus_open_system()</function> does the same, but | |
142 | connects to the system bus. In contrast to | |
143 | <function>sd_bus_default()</function>, | |
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144 | <function>sd_bus_default_user()</function>, and |
145 | <function>sd_bus_default_system()</function>, these calls return | |
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146 | new, independent connection objects that are not associated with |
147 | the invoking thread and are not shared between multiple | |
148 | invocations. It is recommended to share connections per thread to | |
149 | efficiently make use the available resources. Thus, it is | |
150 | recommended to use <function>sd_bus_default()</function>, | |
db2df898 | 151 | <function>sd_bus_default_user()</function> and |
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152 | <function>sd_bus_default_system()</function> to connect to the |
153 | user or system buses.</para> | |
154 | ||
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155 | <para>If the <varname>$DBUS_SESSION_BUS_ADDRESS</varname> environment |
156 | variable is set | |
5eef597e | 157 | (cf. <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>), |
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158 | it will be used as the address of the user bus. This variable can |
159 | contain multiple addresses separated by <literal>;</literal>. If | |
160 | this variable is not set, a suitable default for the default user | |
161 | D-Bus instance will be used.</para> | |
162 | ||
e3bff60a MP |
163 | <para>If the <varname>$DBUS_SYSTEM_BUS_ADDRESS</varname> |
164 | environment variable is set, it will be used as the address of the | |
165 | system bus. This variable uses the same syntax as | |
166 | <varname>$DBUS_SESSION_BUS_ADDRESS</varname>. If this variable is | |
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167 | not set, a suitable default for the default system D-Bus instance |
168 | will be used.</para> | |
169 | ||
f5e65279 MB |
170 | <para><function>sd_bus_open_system_remote()</function> connects to the system bus on |
171 | the specified host using | |
172 | <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>. | |
173 | <parameter>host</parameter> consists of an optional user name followed by the | |
174 | <literal>@</literal> symbol, and the hostname, optionally followed by a | |
175 | <literal>:</literal> and a machine name. If the machine name is given, a connection | |
176 | is created to the system bus in the specified container on the remote machine, and | |
177 | otherwise a connection to the system bus on the specified host is created.</para> | |
178 | ||
179 | <para>Note that entering a container is a privileged operation, and will likely only | |
180 | work for the root user on the remote machine.</para> | |
60f067b4 | 181 | |
fb183854 | 182 | <para><function>sd_bus_open_system_machine()</function> connects |
f47781d8 | 183 | to the system bus in the specified <parameter>machine</parameter>, |
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184 | where <parameter>machine</parameter> is the name of a local |
185 | container. See | |
60f067b4 | 186 | <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
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187 | for more information about the "machine" concept. Note that |
188 | connections into local containers are only available to privileged | |
189 | processes at this time.</para> | |
190 | ||
191 | <para>These calls allocate a bus connection object and initiate | |
192 | the connection to a well-known bus of some form. An alternative to | |
193 | using these high-level calls is to create an unconnected bus | |
194 | object with | |
195 | <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
196 | and to connect it with | |
197 | <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
198 | </para> | |
60f067b4 | 199 | |
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200 | </refsect1> |
201 | ||
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202 | <refsect1> |
203 | <title>Reference ownership</title> | |
fb183854 MP |
204 | <para>The functions <function>sd_bus_open()</function>, |
205 | <function>sd_bus_open_user()</function>, | |
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206 | <function>sd_bus_open_system()</function>, |
207 | <function>sd_bus_open_system_remote()</function>, and | |
208 | <function>sd_bus_open_system_machine()</function> return a new | |
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209 | connection object and the caller owns the sole reference. When not |
210 | needed anymore, this reference should be destroyed with | |
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211 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
212 | </para> | |
213 | ||
e3bff60a MP |
214 | <para>The functions <function>sd_bus_default()</function>, |
215 | <function>sd_bus_default_user()</function> and | |
216 | <function>sd_bus_default_system()</function> do not necessarily | |
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217 | create a new object, but increase the connection reference of an |
218 | existing connection object by one. Use | |
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219 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
220 | to drop the reference.</para> | |
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221 | |
222 | <para>Queued but unwritten/unread messages also keep a reference | |
223 | to their bus connection object. For this reason, even if an | |
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224 | application dropped all references to a bus connection, it might |
225 | not get destroyed right away. Until all incoming queued | |
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226 | messages are read, and until all outgoing unwritten messages are |
227 | written, the bus object will stay | |
228 | alive. <function>sd_bus_flush()</function> may be used to write | |
229 | all outgoing queued messages so they drop their references. To | |
db2df898 | 230 | flush the unread incoming messages, use |
7035cd9e | 231 | <function>sd_bus_close()</function>, which will also close the bus |
db2df898 | 232 | connection. When using the default bus logic, it is a good idea to |
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233 | first invoke <function>sd_bus_flush()</function> followed by |
234 | <function>sd_bus_close()</function> when a thread or process | |
235 | terminates, and thus its bus connection object should be | |
236 | freed.</para> | |
237 | ||
db2df898 | 238 | <para>The life cycle of the default bus connection should be the |
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239 | responsibility of the code that creates/owns the thread the |
240 | default bus connection object is associated with. Library code | |
241 | should neither call <function>sd_bus_flush()</function> nor | |
242 | <function>sd_bus_close()</function> on default bus objects unless | |
243 | it does so in its own private, self-allocated thread. Library code | |
244 | should not use the default bus object in other threads unless it | |
db2df898 | 245 | is clear that the program using it will life cycle the bus |
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246 | connection object and flush and close it before exiting from the |
247 | thread. In libraries where it is not clear that the calling | |
db2df898 | 248 | program will life cycle the bus connection object, it is hence |
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249 | recommended to use <function>sd_bus_open_system()</function> |
250 | instead of <function>sd_bus_default_system()</function> and | |
251 | related calls.</para> | |
252 | </refsect1> | |
253 | ||
254 | <refsect1> | |
255 | <title>Return Value</title> | |
256 | ||
257 | <para>On success, these calls return 0 or a positive | |
258 | integer. On failure, these calls return a negative | |
259 | errno-style error code.</para> | |
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260 | </refsect1> |
261 | ||
262 | <refsect1> | |
263 | <title>Errors</title> | |
264 | ||
265 | <para>Returned errors may indicate the following problems:</para> | |
266 | ||
267 | <variablelist> | |
268 | ||
269 | <varlistentry> | |
5eef597e | 270 | <term><constant>-EINVAL</constant></term> |
60f067b4 | 271 | |
e3bff60a | 272 | <listitem><para>The specified parameters are invalid.</para></listitem> |
60f067b4 JS |
273 | </varlistentry> |
274 | ||
275 | <varlistentry> | |
5eef597e | 276 | <term><constant>-ENOMEM</constant></term> |
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277 | |
278 | <listitem><para>Memory allocation failed.</para></listitem> | |
279 | </varlistentry> | |
280 | ||
e3bff60a MP |
281 | <varlistentry> |
282 | <term><constant>-ESOCKTNOSUPPORT</constant></term> | |
283 | ||
284 | <listitem><para>The protocol version required to connect to the selected bus is not supported.</para></listitem> | |
285 | </varlistentry> | |
60f067b4 | 286 | </variablelist> |
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287 | |
288 | <para>In addition, any further connection-related errors may be | |
289 | by returned. See <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
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290 | </refsect1> |
291 | ||
292 | <refsect1> | |
293 | <title>Notes</title> | |
294 | ||
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295 | <para><function>sd_bus_open_user()</function> and the other |
296 | functions described here are available as a shared library, which | |
297 | can be compiled and linked to with the | |
298 | <constant>libsystemd</constant> <citerefentry | |
299 | project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
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300 | file.</para> |
301 | </refsect1> | |
302 | ||
303 | <refsect1> | |
304 | <title>See Also</title> | |
305 | ||
306 | <para> | |
307 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
308 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
309 | <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
310 | <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
311 | <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
e3bff60a | 312 | <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
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313 | <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
314 | <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
315 | </para> | |
316 | </refsect1> | |
317 | ||
318 | </refentry> |