<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- This file is part of systemd. Copyright 2014 Zbigniew Jędrzejewski-Szmek systemd is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. systemd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with systemd; If not, see <http://www.gnu.org/licenses/>. --> <refentry id="sd_bus_new"> <refentryinfo> <title>sd_bus_new</title> <productname>systemd</productname> <authorgroup> <author> <contrib>A monkey with a typewriter</contrib> <firstname>Zbigniew</firstname> <surname>Jędrzejewski-Szmek</surname> <email>zbyszek@in.waw.pl</email> </author> </authorgroup> </refentryinfo> <refmeta> <refentrytitle>sd_bus_new</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_bus_new</refname> <refname>sd_bus_ref</refname> <refname>sd_bus_unref</refname> <refname>sd_bus_unrefp</refname> <refpurpose>Create a new bus object and create or destroy references to it</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> <funcprototype> <funcdef>int <function>sd_bus_new</function></funcdef> <paramdef>sd_bus **<parameter>bus</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>void <function>sd_bus_unrefp</function></funcdef> <paramdef>sd_bus **<parameter>bus</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_bus_new()</function> creates a new bus object. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference and the bus object will not be connected to any bus. To connect it to a bus, make sure to set an address with <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry> or a related call, and then start the connection with <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> <para>In most cases, it is a better idea to invoke <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry> or related calls instead of the more low-level <function>sd_bus_new()</function> and <function>sd_bus_start()</function>. The higher-level calls not only allocate a bus object but also start the connection to a well-known bus in a single function invocation.</para> <para><function>sd_bus_ref()</function> increases the reference counter of <parameter>bus</parameter> by one.</para> <para><function>sd_bus_unref()</function> decreases the reference counter of <parameter>bus</parameter> by one. Once the reference count has dropped to zero, <parameter>bus</parameter> is destroyed and cannot be used anymore, so further calls to <function>sd_bus_ref()</function> or <function>sd_bus_unref()</function> are illegal.</para> <para><function>sd_bus_unrefp()</function> is similar to <function>sd_bus_unref()</function> but takes a pointer to a pointer to an <type>sd_bus</type> object. This call is useful in conjunction with GCC's and LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable Attribute</ulink>. Note that this function is defined as inline function. Use a declaration like the following, in order to allocate a bus object that is freed automatically as the code block is left:</para> <programlisting>{ __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL; int r; … r = sd_bus_default(&bus); if (r < 0) fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r)); … }</programlisting> <para><function>sd_bus_ref()</function>, <function>sd_bus_unref()</function> and <function>sd_bus_unrefp()</function> execute no operation if the passed in bus object is <constant>NULL</constant>.</para> </refsect1> <refsect1> <title>Return Value</title> <para>On success, <function>sd_bus_new()</function> returns 0 or a positive integer. On failure, it returns a negative errno-style error code.</para> <para><function>sd_bus_ref()</function> always returns the argument. </para> <para><function>sd_bus_unref()</function> always returns <constant>NULL</constant>.</para> </refsect1> <refsect1> <title>Errors</title> <para>Returned errors may indicate the following problems:</para> <variablelist> <varlistentry> <term><constant>-ENOMEM</constant></term> <listitem><para>Memory allocation failed.</para></listitem> </varlistentry> </variablelist> </refsect1> <refsect1> <title>Notes</title> <para><function>sd_bus_new()</function> and other functions described here are available as a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> </refsect1> <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>