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-<?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_default">
-
- <refentryinfo>
- <title>sd_bus_default</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_default</refentrytitle>
- <manvolnum>3</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>sd_bus_default</refname>
- <refname>sd_bus_default_user</refname>
- <refname>sd_bus_default_system</refname>
-
- <refname>sd_bus_open</refname>
- <refname>sd_bus_open_user</refname>
- <refname>sd_bus_open_system</refname>
- <refname>sd_bus_open_system_remote</refname>
- <refname>sd_bus_open_system_machine</refname>
-
- <refpurpose>Acquire a connection to a system or user bus</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_default</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_default_user</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_default_system</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_open</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_open_user</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_open_system</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_open_system_remote</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- <paramdef>const char *<parameter>host</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_bus_open_system_machine</function></funcdef>
- <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
- <paramdef>const char *<parameter>machine</parameter></paramdef>
- </funcprototype>
-
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para><function>sd_bus_default()</function> acquires a bus
- connection object to the user bus when invoked in user context, or
- to the system bus otherwise. The connection object is associated
- with the calling thread. Each time the function is invoked from
- the same thread, the same object is returned, but its reference
- count is increased by one, as long as at least one reference is
- kept. When the last reference to the connection is dropped (using
- the
- <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- call), the connection is terminated. Note that the connection is
- not automatically terminated when the associated thread ends. It
- is important to drop the last reference to the bus connection
- explicitly before the thread ends, as otherwise, the connection will
- leak. Also, queued but unread or unwritten messages keep the
- bus referenced, see below.</para>
-
- <para><function>sd_bus_default_user()</function> returns a user
- bus connection object associated with the calling thread.
- <function>sd_bus_default_system()</function> is similar, but
- connects to the system bus. Note that
- <function>sd_bus_default()</function> is identical to these two
- calls, depending on the execution context.</para>
-
- <para><function>sd_bus_open()</function> creates a new,
- independent bus connection to the user bus when invoked in user
- context, or the system bus
- otherwise. <function>sd_bus_open_user()</function> is similar, but
- connects only to the user bus.
- <function>sd_bus_open_system()</function> does the same, but
- connects to the system bus. In contrast to
- <function>sd_bus_default()</function>,
- <function>sd_bus_default_user()</function>, and
- <function>sd_bus_default_system()</function>, these calls return
- new, independent connection objects that are not associated with
- the invoking thread and are not shared between multiple
- invocations. It is recommended to share connections per thread to
- efficiently make use the available resources. Thus, it is
- recommended to use <function>sd_bus_default()</function>,
- <function>sd_bus_default_user()</function> and
- <function>sd_bus_default_system()</function> to connect to the
- user or system buses.</para>
-
- <para>If the <varname>$DBUS_SESSION_BUS_ADDRESS</varname> environment
- variable is set
- (cf. <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
- it will be used as the address of the user bus. This variable can
- contain multiple addresses separated by <literal>;</literal>. If
- this variable is not set, a suitable default for the default user
- D-Bus instance will be used.</para>
-
- <para>If the <varname>$DBUS_SYSTEM_BUS_ADDRESS</varname>
- environment variable is set, it will be used as the address of the
- system bus. This variable uses the same syntax as
- <varname>$DBUS_SESSION_BUS_ADDRESS</varname>. If this variable is
- not set, a suitable default for the default system D-Bus instance
- will be used.</para>
-
- <para><function>sd_bus_open_system_remote()</function> connects to
- the system bus on the specified <parameter>host</parameter> using
- <citerefentry
- project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <parameter>host</parameter>
- consists of an optional user name followed by the
- <literal>@</literal> symbol, and the hostname.
- </para>
-
- <para><function>sd_bus_open_system_machine()</function> connects
- to the system bus in the specified <parameter>machine</parameter>,
- where <parameter>machine</parameter> is the name of a local
- container. See
- <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- for more information about the "machine" concept. Note that
- connections into local containers are only available to privileged
- processes at this time.</para>
-
- <para>These calls allocate a bus connection object and initiate
- the connection to a well-known bus of some form. An alternative to
- using these high-level calls is to create an unconnected bus
- object with
- <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- and to connect it with
- <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
- </para>
-
- </refsect1>
-
- <refsect1>
- <title>Reference ownership</title>
- <para>The functions <function>sd_bus_open()</function>,
- <function>sd_bus_open_user()</function>,
- <function>sd_bus_open_system()</function>,
- <function>sd_bus_open_system_remote()</function>, and
- <function>sd_bus_open_system_machine()</function> return a new
- connection object and the caller owns the sole reference. When not
- needed anymore, this reference should be destroyed with
- <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
- </para>
-
- <para>The functions <function>sd_bus_default()</function>,
- <function>sd_bus_default_user()</function> and
- <function>sd_bus_default_system()</function> do not necessarily
- create a new object, but increase the connection reference of an
- existing connection object by one. Use
- <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- to drop the reference.</para>
-
- <para>Queued but unwritten/unread messages also keep a reference
- to their bus connection object. For this reason, even if an
- application dropped all references to a bus connection, it might
- not get destroyed right away. Until all incoming queued
- messages are read, and until all outgoing unwritten messages are
- written, the bus object will stay
- alive. <function>sd_bus_flush()</function> may be used to write
- all outgoing queued messages so they drop their references. To
- flush the unread incoming messages, use
- <function>sd_bus_close()</function>, which will also close the bus
- connection. When using the default bus logic, it is a good idea to
- first invoke <function>sd_bus_flush()</function> followed by
- <function>sd_bus_close()</function> when a thread or process
- terminates, and thus its bus connection object should be
- freed.</para>
-
- <para>The life cycle of the default bus connection should be the
- responsibility of the code that creates/owns the thread the
- default bus connection object is associated with. Library code
- should neither call <function>sd_bus_flush()</function> nor
- <function>sd_bus_close()</function> on default bus objects unless
- it does so in its own private, self-allocated thread. Library code
- should not use the default bus object in other threads unless it
- is clear that the program using it will life cycle the bus
- connection object and flush and close it before exiting from the
- thread. In libraries where it is not clear that the calling
- program will life cycle the bus connection object, it is hence
- recommended to use <function>sd_bus_open_system()</function>
- instead of <function>sd_bus_default_system()</function> and
- related calls.</para>
- </refsect1>
-
- <refsect1>
- <title>Return Value</title>
-
- <para>On success, these calls return 0 or a positive
- integer. On failure, these calls return a negative
- errno-style error code.</para>
- </refsect1>
-
- <refsect1>
- <title>Errors</title>
-
- <para>Returned errors may indicate the following problems:</para>
-
- <variablelist>
-
- <varlistentry>
- <term><constant>-EINVAL</constant></term>
-
- <listitem><para>The specified parameters are invalid.</para></listitem>
- </varlistentry>
-
- <varlistentry>
- <term><constant>-ENOMEM</constant></term>
-
- <listitem><para>Memory allocation failed.</para></listitem>
- </varlistentry>
-
- <varlistentry>
- <term><constant>-ESOCKTNOSUPPORT</constant></term>
-
- <listitem><para>The protocol version required to connect to the selected bus is not supported.</para></listitem>
- </varlistentry>
- </variablelist>
-
- <para>In addition, any further connection-related errors may be
- by returned. See <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
- </refsect1>
-
- <refsect1>
- <title>Notes</title>
-
- <para><function>sd_bus_open_user()</function> and the 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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- </para>
- </refsect1>
-
-</refentry>