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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+ --> | |
5 | ||
6 | <refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
7 | ||
8 | <refentryinfo> | |
9 | <title>sd_bus_new</title> | |
10 | <productname>systemd</productname> | |
11 | </refentryinfo> | |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_bus_new</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_bus_new</refname> | |
20 | <refname>sd_bus_ref</refname> | |
21 | <refname>sd_bus_unref</refname> | |
22 | <refname>sd_bus_unrefp</refname> | |
23 | <refname>sd_bus_close_unref</refname> | |
24 | <refname>sd_bus_close_unrefp</refname> | |
25 | <refname>sd_bus_flush_close_unref</refname> | |
26 | <refname>sd_bus_flush_close_unrefp</refname> | |
27 | ||
28 | <refpurpose>Create a new bus object and create or destroy references to it</refpurpose> | |
29 | </refnamediv> | |
30 | ||
31 | <refsynopsisdiv> | |
32 | <funcsynopsis> | |
33 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
34 | ||
35 | <funcprototype> | |
36 | <funcdef>int <function>sd_bus_new</function></funcdef> | |
37 | <paramdef>sd_bus **<parameter>bus</parameter></paramdef> | |
38 | </funcprototype> | |
39 | ||
40 | <funcprototype> | |
41 | <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef> | |
42 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
43 | </funcprototype> | |
44 | ||
45 | <funcprototype> | |
46 | <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef> | |
47 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
48 | </funcprototype> | |
49 | ||
50 | <funcprototype> | |
51 | <funcdef>sd_bus *<function>sd_bus_close_unref</function></funcdef> | |
52 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
53 | </funcprototype> | |
54 | ||
55 | <funcprototype> | |
56 | <funcdef>sd_bus *<function>sd_bus_flush_close_unref</function></funcdef> | |
57 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
58 | </funcprototype> | |
59 | ||
60 | <funcprototype> | |
61 | <funcdef>void <function>sd_bus_unrefp</function></funcdef> | |
62 | <paramdef>sd_bus **<parameter>busp</parameter></paramdef> | |
63 | </funcprototype> | |
64 | ||
65 | <funcprototype> | |
66 | <funcdef>void <function>sd_bus_close_unrefp</function></funcdef> | |
67 | <paramdef>sd_bus **<parameter>busp</parameter></paramdef> | |
68 | </funcprototype> | |
69 | ||
70 | <funcprototype> | |
71 | <funcdef>void <function>sd_bus_flush_close_unrefp</function></funcdef> | |
72 | <paramdef>sd_bus **<parameter>busp</parameter></paramdef> | |
73 | </funcprototype> | |
74 | </funcsynopsis> | |
75 | </refsynopsisdiv> | |
76 | ||
77 | <refsect1> | |
78 | <title>Description</title> | |
79 | ||
80 | <para><function>sd_bus_new()</function> creates a new bus | |
81 | object. This object is reference-counted, and will be destroyed | |
82 | when all references are gone. Initially, the caller of this | |
83 | function owns the sole reference and the bus object will not be | |
84 | connected to any bus. To connect it to a bus, make sure | |
85 | to set an address with | |
86 | <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
87 | or a related call, and then start the connection with | |
88 | <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
89 | ||
90 | <para>In most cases, it is a better idea to invoke | |
91 | <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
92 | <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
93 | or related calls instead of the more low-level | |
94 | <function>sd_bus_new()</function> and | |
95 | <function>sd_bus_start()</function>. The higher-level calls not | |
96 | only allocate a bus object but also start the connection to a | |
97 | well-known bus in a single function invocation.</para> | |
98 | ||
99 | <para><function>sd_bus_ref()</function> increases the reference | |
100 | counter of <parameter>bus</parameter> by one.</para> | |
101 | ||
102 | <para><function>sd_bus_unref()</function> decreases the reference | |
103 | counter of <parameter>bus</parameter> by one. Once the reference | |
104 | count has dropped to zero, <parameter>bus</parameter> is destroyed | |
105 | and cannot be used anymore, so further calls to | |
106 | <function>sd_bus_ref()</function> or | |
107 | <function>sd_bus_unref()</function> are illegal.</para> | |
108 | ||
109 | <para><function>sd_bus_unrefp()</function> is similar to | |
110 | <function>sd_bus_unref()</function> but takes a pointer to a | |
111 | pointer to an <type>sd_bus</type> object. This call is useful in | |
112 | conjunction with GCC's and LLVM's <ulink | |
113 | url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up | |
114 | Variable Attribute</ulink>. Note that this function is defined as | |
115 | inline function. Use a declaration like the following, in order to | |
116 | allocate a bus object that is freed automatically as the code | |
117 | block is left:</para> | |
118 | ||
119 | <programlisting>{ | |
120 | __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL; | |
121 | int r; | |
122 | … | |
123 | r = sd_bus_default(&bus); | |
124 | if (r < 0) | |
125 | fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r)); | |
126 | … | |
127 | }</programlisting> | |
128 | ||
129 | <para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function> | |
130 | execute no operation if the passed in bus object address is | |
131 | <constant>NULL</constant>. <function>sd_bus_unrefp()</function> will first | |
132 | dereference its argument, which must not be <constant>NULL</constant>, and will | |
133 | execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>. | |
134 | </para> | |
135 | ||
136 | <para><function>sd_bus_close_unref()</function> is similar to <function>sd_bus_unref()</function>, but | |
137 | first executes | |
138 | <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
139 | ensuring that the connection is terminated before the reference to the connection is dropped and possibly | |
140 | the object freed.</para> | |
141 | ||
142 | <para><function>sd_bus_flush_close_unref()</function> is similar to <function>sd_bus_unref()</function>, | |
143 | but first executes | |
144 | <citerefentry><refentrytitle>sd_bus_flush</refentrytitle><manvolnum>3</manvolnum></citerefentry> as well | |
145 | as <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
146 | ensuring that any pending messages are synchronously flushed out before the reference to the connection | |
147 | is dropped and possibly the object freed. This call is particularly useful immediately before exiting | |
148 | from a program as it ensures that any pending outgoing messages are written out, and unprocessed but | |
149 | queued incoming messages released before the connection is terminated and released.</para> | |
150 | ||
151 | <para><function>sd_bus_close_unrefp()</function> is similar to | |
152 | <function>sd_bus_close_unref()</function>, but may be used in GCC's and LLVM's Clean-up Variable | |
153 | Attribute, see above. Similarly, <function>sd_bus_flush_close_unrefp()</function> is similar to | |
154 | <function>sd_bus_flush_close_unref()</function>.</para> | |
155 | </refsect1> | |
156 | ||
157 | <refsect1> | |
158 | <title>Return Value</title> | |
159 | ||
160 | <para>On success, <function>sd_bus_new()</function> returns 0 or a | |
161 | positive integer. On failure, it returns a negative errno-style | |
162 | error code.</para> | |
163 | ||
164 | <para><function>sd_bus_ref()</function> always returns the argument. | |
165 | </para> | |
166 | ||
167 | <para><function>sd_bus_unref()</function> and <function>sd_bus_flush_close_unref()</function> always return | |
168 | <constant>NULL</constant>.</para> | |
169 | ||
170 | <refsect2> | |
171 | <title>Errors</title> | |
172 | ||
173 | <para>Returned errors may indicate the following problems:</para> | |
174 | ||
175 | <variablelist> | |
176 | <varlistentry> | |
177 | <term><constant>-ENOMEM</constant></term> | |
178 | ||
179 | <listitem><para>Memory allocation failed.</para></listitem> | |
180 | </varlistentry> | |
181 | </variablelist> | |
182 | </refsect2> | |
183 | </refsect1> | |
184 | ||
185 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
186 | ||
187 | <refsect1> | |
188 | <title>See Also</title> | |
189 | ||
190 | <para> | |
191 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
192 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
193 | <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
194 | <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
195 | <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
196 | <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
197 | <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
198 | </para> | |
199 | </refsect1> | |
200 | ||
201 | </refentry> |