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 <refentrytitle>sd_bus_new</refentrytitle>
20 <manvolnum>3</manvolnum>
24 <refname>sd_bus_new</refname>
25 <refname>sd_bus_ref</refname>
26 <refname>sd_bus_unref</refname>
27 <refname>sd_bus_unrefp</refname>
29 <refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
34 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
37 <funcdef>int <function>sd_bus_new</function></funcdef>
38 <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
42 <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
43 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
47 <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
48 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
52 <funcdef>void <function>sd_bus_unrefp</function></funcdef>
53 <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
59 <title>Description</title>
61 <para><function>sd_bus_new()</function> creates a new bus
62 object. This object is reference-counted, and will be destroyed
63 when all references are gone. Initially, the caller of this
64 function owns the sole reference and the bus object will not be
65 connected to any bus. To connect it to a bus, make sure
66 to set an address with
67 <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
68 or a related call, and then start the connection with
69 <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
71 <para>In most cases, it is a better idea to invoke
72 <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
73 <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
74 or related calls instead of the more low-level
75 <function>sd_bus_new()</function> and
76 <function>sd_bus_start()</function>. The higher-level calls not
77 only allocate a bus object but also start the connection to a
78 well-known bus in a single function invocation.</para>
80 <para><function>sd_bus_ref()</function> increases the reference
81 counter of <parameter>bus</parameter> by one.</para>
83 <para><function>sd_bus_unref()</function> decreases the reference
84 counter of <parameter>bus</parameter> by one. Once the reference
85 count has dropped to zero, <parameter>bus</parameter> is destroyed
86 and cannot be used anymore, so further calls to
87 <function>sd_bus_ref()</function> or
88 <function>sd_bus_unref()</function> are illegal.</para>
90 <para><function>sd_bus_unrefp()</function> is similar to
91 <function>sd_bus_unref()</function> but takes a pointer to a
92 pointer to an <type>sd_bus</type> object. This call is useful in
93 conjunction with GCC's and LLVM's <ulink
94 url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
95 Variable Attribute</ulink>. Note that this function is defined as
96 inline function. Use a declaration like the following, in order to
97 allocate a bus object that is freed automatically as the code
101 __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
104 r = sd_bus_default(&bus);
106 fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
110 <para><function>sd_bus_ref()</function>,
111 <function>sd_bus_unref()</function> and
112 <function>sd_bus_unrefp()</function> execute no operation if the
113 passed in bus object is <constant>NULL</constant>.</para>
117 <title>Return Value</title>
119 <para>On success, <function>sd_bus_new()</function> returns 0 or a
120 positive integer. On failure, it returns a negative errno-style
123 <para><function>sd_bus_ref()</function> always returns the argument.
126 <para><function>sd_bus_unref()</function> always returns
127 <constant>NULL</constant>.</para>
131 <title>Errors</title>
133 <para>Returned errors may indicate the following problems:</para>
137 <term><constant>-ENOMEM</constant></term>
139 <listitem><para>Memory allocation failed.</para></listitem>
144 <xi:include href="libelogind-pkgconfig.xml" />
147 <title>See Also</title>
150 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
151 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
152 <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
153 <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
154 <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
155 <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>