man/sd_bus_new.xml

   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">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
  11
  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.
  16
  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.
  21
  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/>.
  24 -->
  25
  26 <refentry id="sd_bus_new">
  27
  28   <refentryinfo>
  29     <title>sd_bus_new</title>
  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>
  43     <refentrytitle>sd_bus_new</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_bus_new</refname>
  49     <refname>sd_bus_ref</refname>
  50     <refname>sd_bus_unref</refname>
  51     <refname>sd_bus_unrefp</refname>
  52
  53     <refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
  54   </refnamediv>
  55
  56   <refsynopsisdiv>
  57     <funcsynopsis>
  58       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  59
  60       <funcprototype>
  61         <funcdef>int <function>sd_bus_new</function></funcdef>
  62         <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
  63       </funcprototype>
  64
  65       <funcprototype>
  66         <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
  67         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
  72         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  73       </funcprototype>
  74
  75       <funcprototype>
  76         <funcdef>void <function>sd_bus_unrefp</function></funcdef>
  77         <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
  78       </funcprototype>
  79     </funcsynopsis>
  80   </refsynopsisdiv>
  81
  82   <refsect1>
  83     <title>Description</title>
  84
  85     <para><function>sd_bus_new()</function> creates a new bus
  86     object. This object is reference-counted, and will be destroyed
  87     when all references are gone. Initially, the caller of this
  88     function owns the sole reference and the bus object will not be
  89     connected to any bus. To connect it to a bus, make sure
  90     to set an address with
  91     <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  92     or a related call, and then start the connection with
  93     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  94
  95     <para>In most cases, it is a better idea to invoke
  96     <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  97     <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  98     or related calls instead of the more low-level
  99     <function>sd_bus_new()</function> and
 100     <function>sd_bus_start()</function>. The higher-level calls not
 101     only allocate a bus object but also start the connection to a
 102     well-known bus in a single function invocation.</para>
 103
 104     <para><function>sd_bus_ref()</function> increases the reference
 105     counter of <parameter>bus</parameter> by one.</para>
 106
 107     <para><function>sd_bus_unref()</function> decreases the reference
 108     counter of <parameter>bus</parameter> by one. Once the reference
 109     count has dropped to zero, <parameter>bus</parameter> is destroyed
 110     and cannot be used anymore, so further calls to
 111     <function>sd_bus_ref()</function> or
 112     <function>sd_bus_unref()</function> are illegal.</para>
 113
 114     <para><function>sd_bus_unrefp()</function> is similar to
 115     <function>sd_bus_unref()</function> but takes a pointer to a
 116     pointer to an <type>sd_bus</type> object. This call is useful in
 117     conjunction with GCC's and LLVM's <ulink
 118     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 119     Variable Attribute</ulink>. Note that this function is defined as
 120     inline function. Use a declaration like the following, in order to
 121     allocate a bus object that is freed automatically as the code
 122     block is left:</para>
 123
 124     <programlisting>{
 125         __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
 126         int r;
 127         …
 128         r = sd_bus_default(&amp;bus);
 129         if (r &lt; 0)
 130                 fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
 131         …
 132 }</programlisting>
 133
 134     <para><function>sd_bus_ref()</function>,
 135     <function>sd_bus_unref()</function> and
 136     <function>sd_bus_unrefp()</function> execute no operation if the
 137     passed in bus object is <constant>NULL</constant>.</para>
 138   </refsect1>
 139
 140   <refsect1>
 141     <title>Return Value</title>
 142
 143     <para>On success, <function>sd_bus_new()</function> returns 0 or a
 144     positive integer. On failure, it returns a negative errno-style
 145     error code.</para>
 146
 147     <para><function>sd_bus_ref()</function> always returns the argument.
 148     </para>
 149
 150     <para><function>sd_bus_unref()</function> always returns
 151     <constant>NULL</constant>.</para>
 152   </refsect1>
 153
 154   <refsect1>
 155     <title>Errors</title>
 156
 157     <para>Returned errors may indicate the following problems:</para>
 158
 159     <variablelist>
 160       <varlistentry>
 161         <term><constant>-ENOMEM</constant></term>
 162
 163         <listitem><para>Memory allocation failed.</para></listitem>
 164       </varlistentry>
 165     </variablelist>
 166   </refsect1>
 167
 168   <refsect1>
 169     <title>Notes</title>
 170
 171     <para><function>sd_bus_new()</function> and other functions
 172     described here are available as a shared library, which can be
 173     compiled and linked to with the
 174     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 175     file.</para>
 176   </refsect1>
 177
 178   <refsect1>
 179     <title>See Also</title>
 180
 181     <para>
 182       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 184       <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 185       <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 186       <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 187       <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 188     </para>
 189   </refsect1>
 190
 191 </refentry>