--- /dev/null
+<?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 <systemd/sd-bus.h></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>libelogind</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>
~ianmdlvl / elogind.git / blobdiff