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787f78b6a1
Moving them out makes it easier to run them through a compiler, use automatic indentation, and opens the possibility to provide a download link in the future. I verified that all examples compile cleanly. (2-space indentation is used because the examples are already significantly indented in the man page, and we need to keep them narrow so that they display well on standard terminals.)
160 lines
5.9 KiB
XML
160 lines
5.9 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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-->
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<refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_new</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_new</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_new</refname>
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<refname>sd_bus_ref</refname>
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<refname>sd_bus_unref</refname>
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<refname>sd_bus_unrefp</refname>
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<refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_bus_new</function></funcdef>
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<paramdef>sd_bus **<parameter>bus</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_bus_unrefp</function></funcdef>
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<paramdef>sd_bus **<parameter>busp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_new()</function> creates a new bus
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object. This object is reference-counted, and will be destroyed
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when all references are gone. Initially, the caller of this
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function owns the sole reference and the bus object will not be
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connected to any bus. To connect it to a bus, make sure
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to set an address with
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<citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or a related call, and then start the connection with
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<citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>In most cases, it is a better idea to invoke
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<citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or related calls instead of the more low-level
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<function>sd_bus_new()</function> and
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<function>sd_bus_start()</function>. The higher-level calls not
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only allocate a bus object but also start the connection to a
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well-known bus in a single function invocation.</para>
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<para><function>sd_bus_ref()</function> increases the reference
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counter of <parameter>bus</parameter> by one.</para>
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<para><function>sd_bus_unref()</function> decreases the reference
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counter of <parameter>bus</parameter> by one. Once the reference
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count has dropped to zero, <parameter>bus</parameter> is destroyed
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and cannot be used anymore, so further calls to
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<function>sd_bus_ref()</function> or
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<function>sd_bus_unref()</function> are illegal.</para>
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<para><function>sd_bus_unrefp()</function> is similar to
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<function>sd_bus_unref()</function> but takes a pointer to a
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pointer to an <type>sd_bus</type> object. This call is useful in
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conjunction with GCC's and LLVM's <ulink
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url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
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Variable Attribute</ulink>. Note that this function is defined as
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inline function. Use a declaration like the following, in order to
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allocate a bus object that is freed automatically as the code
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block is left:</para>
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<programlisting>{
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__attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
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int r;
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…
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r = sd_bus_default(&bus);
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if (r < 0)
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fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
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…
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}</programlisting>
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<para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function>
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execute no operation if the passed in bus object address is
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<constant>NULL</constant>. <function>sd_bus_unrefp()</function> will first
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dereference its argument, which must not be <constant>NULL</constant>, and will
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execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>.
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_bus_new()</function> returns 0 or a
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positive integer. On failure, it returns a negative errno-style
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error code.</para>
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<para><function>sd_bus_ref()</function> always returns the argument.
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</para>
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<para><function>sd_bus_unref()</function> always returns
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<constant>NULL</constant>.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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