mirror of
https://github.com/systemd/systemd.git
synced 2024-11-24 10:43:35 +08:00
313 lines
13 KiB
XML
313 lines
13 KiB
XML
<?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>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>
|