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bd62b74486
It's similar to sd_bus_flush_close_unref() but doesn't do the flushing. This is useful since this will still discnnect the connection properly but not synchronously wait for the peer to take our messages. Primary usecase is within _cleanup_() expressions where synchronously waiting on the peer is not OK.
205 lines
8.4 KiB
XML
205 lines
8.4 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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<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 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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<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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</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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<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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