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200 lines
8.4 KiB
XML
200 lines
8.4 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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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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<refname>sd_bus_close_unref</refname>
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<refname>sd_bus_close_unrefp</refname>
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<refname>sd_bus_flush_close_unref</refname>
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<refname>sd_bus_flush_close_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>sd_bus *<function>sd_bus_close_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>sd_bus *<function>sd_bus_flush_close_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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<funcprototype>
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<funcdef>void <function>sd_bus_close_unrefp</function></funcdef>
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<paramdef>sd_bus **<parameter>busp</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_bus_flush_close_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 better to use
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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 <function>sd_bus_new()</function> and
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<function>sd_bus_start()</function>. The higher-level functions not only allocate a bus object but also
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start the connection to a well-known bus in a single function call.</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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<para><function>sd_bus_close_unref()</function> is similar to <function>sd_bus_unref()</function>, but
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first executes
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<citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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ensuring that the connection is terminated before the reference to the connection is dropped and possibly
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the object freed.</para>
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<para><function>sd_bus_flush_close_unref()</function> is similar to <function>sd_bus_unref()</function>,
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but first executes
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<citerefentry><refentrytitle>sd_bus_flush</refentrytitle><manvolnum>3</manvolnum></citerefentry> as well
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as <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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ensuring that any pending messages are synchronously flushed out before the reference to the connection
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is dropped and possibly the object freed. This call is particularly useful immediately before exiting
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from a program as it ensures that any pending outgoing messages are written out, and unprocessed but
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queued incoming messages released before the connection is terminated and released.</para>
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<para><function>sd_bus_close_unrefp()</function> is similar to
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<function>sd_bus_close_unref()</function>, but may be used in GCC's and LLVM's Clean-up Variable
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Attribute, see above. Similarly, <function>sd_bus_flush_close_unrefp()</function> is similar to
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<function>sd_bus_flush_close_unref()</function>.</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> and <function>sd_bus_flush_close_unref()</function> always return
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<constant>NULL</constant>.</para>
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<refsect2>
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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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</refsect2>
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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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<citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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