mirror of
https://github.com/systemd/systemd.git
synced 2024-12-14 04:33:37 +08:00
b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
323 lines
16 KiB
XML
323 lines
16 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
|
|
|
|
<refentry id="sd_bus_default" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_bus_default</title>
|
|
<productname>systemd</productname>
|
|
</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_with_description</refname>
|
|
<refname>sd_bus_open_user</refname>
|
|
<refname>sd_bus_open_user_with_description</refname>
|
|
<refname>sd_bus_open_system</refname>
|
|
<refname>sd_bus_open_system_with_description</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_with_description</function></funcdef>
|
|
<paramdef>sd_bus **<parameter>bus</parameter></paramdef>
|
|
<paramdef>const char *<parameter>description</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_user_with_description</function></funcdef>
|
|
<paramdef>sd_bus **<parameter>bus</parameter></paramdef>
|
|
<paramdef>const char *<parameter>description</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_with_description</function></funcdef>
|
|
<paramdef>sd_bus **<parameter>bus</parameter></paramdef>
|
|
<paramdef>const char *<parameter>description</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><function>sd_bus_open_with_description()</function>,
|
|
<function>sd_bus_open_user_with_description()</function>, and
|
|
<function>sd_bus_open_system_with_description()</function> are similar to
|
|
<function>sd_bus_open()</function>, <function>sd_bus_open_user()</function>, and
|
|
<function>sd_bus_open_system()</function>, but allow a description string to be set, see
|
|
<citerefentry><refentrytitle>sd_bus_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
|
|
<parameter>description</parameter> may be <constant>NULL</constant>, in which case this function
|
|
is equivalent to <function>sd_bus_open()</function>. This description string is used in log
|
|
messages about the bus object, and including a "name" for the bus makes them easier to
|
|
understand. Some messages are emitted during bus initialization, hence using this function is
|
|
prefereable to setting the description later with
|
|
<function>sd_bus_open_with_description()</function>. The argument is copied internally and will
|
|
not be referenced after the function returns.</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 host 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, optionally followed by a
|
|
<literal>:</literal> and a port, optionally followed by a
|
|
<literal>/</literal> and a machine name. If the machine name is given, a connection
|
|
is created to the system bus in the specified container on the remote machine, and
|
|
otherwise a connection to the system bus on the specified host is created.</para>
|
|
|
|
<para>Note that entering a container is a privileged operation, and will likely only
|
|
work for the root user on the remote machine.</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 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>Normally, slot objects (as created by
|
|
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> and similar
|
|
calls) keep a reference to their bus connection object, too. Thus, as long as a bus slot object remains referenced
|
|
its bus object will remain allocated too. Optionally, bus slot objects may be placed in "floating" mode. When in
|
|
floating mode the life cycle of the bus slot object is bound to the bus object, i.e. when the bus object is freed
|
|
the bus slot object is automatically unreferenced too. The floating state of a slot object may be controlled
|
|
explicitly with
|
|
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
though usually floating bus slot objects are created by passing <constant>NULL</constant> as the
|
|
<parameter>slot</parameter> parameter of <function>sd_bus_add_match()</function> and related calls, thus indicating
|
|
that the caller is not directly interested in referencing and managing the bus slot object.</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>
|
|
|
|
<refsect2>
|
|
<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>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" />
|
|
|
|
<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>
|