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">
6 SPDX-License-Identifier: LGPL-2.1+
8 Copyright © 2014 Zbigniew Jędrzejewski-Szmek
11 <refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude">
14 <title>sd_bus_new</title>
15 <productname>systemd</productname>
19 <contrib>A monkey with a typewriter</contrib>
20 <firstname>Zbigniew</firstname>
21 <surname>Jędrzejewski-Szmek</surname>
22 <email>zbyszek@in.waw.pl</email>
28 <refentrytitle>sd_bus_new</refentrytitle>
29 <manvolnum>3</manvolnum>
33 <refname>sd_bus_new</refname>
34 <refname>sd_bus_ref</refname>
35 <refname>sd_bus_unref</refname>
36 <refname>sd_bus_unrefp</refname>
38 <refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
43 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
46 <funcdef>int <function>sd_bus_new</function></funcdef>
47 <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
51 <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
52 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
56 <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
57 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
61 <funcdef>void <function>sd_bus_unrefp</function></funcdef>
62 <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
68 <title>Description</title>
70 <para><function>sd_bus_new()</function> creates a new bus
71 object. This object is reference-counted, and will be destroyed
72 when all references are gone. Initially, the caller of this
73 function owns the sole reference and the bus object will not be
74 connected to any bus. To connect it to a bus, make sure
75 to set an address with
76 <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
77 or a related call, and then start the connection with
78 <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
80 <para>In most cases, it is a better idea to invoke
81 <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
82 <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
83 or related calls instead of the more low-level
84 <function>sd_bus_new()</function> and
85 <function>sd_bus_start()</function>. The higher-level calls not
86 only allocate a bus object but also start the connection to a
87 well-known bus in a single function invocation.</para>
89 <para><function>sd_bus_ref()</function> increases the reference
90 counter of <parameter>bus</parameter> by one.</para>
92 <para><function>sd_bus_unref()</function> decreases the reference
93 counter of <parameter>bus</parameter> by one. Once the reference
94 count has dropped to zero, <parameter>bus</parameter> is destroyed
95 and cannot be used anymore, so further calls to
96 <function>sd_bus_ref()</function> or
97 <function>sd_bus_unref()</function> are illegal.</para>
99 <para><function>sd_bus_unrefp()</function> is similar to
100 <function>sd_bus_unref()</function> but takes a pointer to a
101 pointer to an <type>sd_bus</type> object. This call is useful in
102 conjunction with GCC's and LLVM's <ulink
103 url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
104 Variable Attribute</ulink>. Note that this function is defined as
105 inline function. Use a declaration like the following, in order to
106 allocate a bus object that is freed automatically as the code
107 block is left:</para>
110 __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
113 r = sd_bus_default(&bus);
115 fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
119 <para><function>sd_bus_ref()</function>,
120 <function>sd_bus_unref()</function> and
121 <function>sd_bus_unrefp()</function> execute no operation if the
122 passed in bus object is <constant>NULL</constant>.</para>
126 <title>Return Value</title>
128 <para>On success, <function>sd_bus_new()</function> returns 0 or a
129 positive integer. On failure, it returns a negative errno-style
132 <para><function>sd_bus_ref()</function> always returns the argument.
135 <para><function>sd_bus_unref()</function> always returns
136 <constant>NULL</constant>.</para>
140 <title>Errors</title>
142 <para>Returned errors may indicate the following problems:</para>
146 <term><constant>-ENOMEM</constant></term>
148 <listitem><para>Memory allocation failed.</para></listitem>
153 <xi:include href="libelogind-pkgconfig.xml" />
156 <title>See Also</title>
159 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
160 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
161 <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
162 <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
163 <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
164 <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>