-<?xml version='1.0'?> <!--*-nxml-*-->
+<?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.
+ This file is part of systemd.
-Copyright 2014 Zbigniew Jędrzejewski-Szmek
+ 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 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.
+ 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/>.
+ 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">
<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>
<funcprototype>
<funcdef>int <function>sd_bus_new</function></funcdef>
- <paramdef>sd_bus
** <parameter>bus</parameter></paramdef>
+ <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>
+ <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>
+ <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>
<title>Description</title>
<para><function>sd_bus_new()</function> creates a new bus
- object. This object is reference counted, and will be destroyed
+ 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.</para>
-
- <para><function>sd_bus_ref()</function> creates a new reference to
- <parameter>bus</parameter>. This bus object will not be destroyed
- until <function>sd_bus_unref()</function> has been called as many
- times plus once more. Once the reference count has dropped to
- zero, <parameter>bus</parameter> cannot be used anymore, so
- further calls to <function>sd_bus_ref()</function> or
+ 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_unref()</function> destroys a reference to
- <parameter>bus</parameter>.</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>
positive integer. On failure, it returns a negative errno-style
error code.</para>
- <para><function>sd_bus_ref</function> always returns the argument.
+ <para><function>sd_bus_ref()</function> always returns the argument.
</para>
- <para><function>sd_bus_unref</function> always returns
+ <para><function>sd_bus_unref()</function> always returns
<constant>NULL</constant>.</para>
</refsect1>
<variablelist>
<varlistentry>
- <term><varname>-ENOMEM</varname></term>
+ <term><constant>-ENOMEM</constant></term>
<listitem><para>Memory allocation failed.</para></listitem>
</varlistentry>
<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><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ <constant>libelogind</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-bus</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>,
<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_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>
~ianmdlvl / elogind.git / blobdiff