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<?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-or-later -->
<refentry id="sd_bus_call"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_call</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_call</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_call</refname>
<refname>sd_bus_call_async</refname>
<refpurpose>Invoke a D-Bus method call</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<xi:include href="sd_bus_add_match.xml" xpointer="sd_bus_message_handler_t"/>
<funcprototype>
<funcdef>int <function>sd_bus_call</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>uint64_t <parameter>usec</parameter></paramdef>
<paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
<paramdef>sd_bus_message **<parameter>reply</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_call_async</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
<paramdef>uint64_t <parameter>usec</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_call()</function> takes a complete bus message object and calls the
corresponding D-Bus method. On success, the response is stored in <parameter>reply</parameter>.
<parameter>usec</parameter> indicates the timeout in microseconds. If
<parameter>ret_error</parameter> is not <constant>NULL</constant> and
<function>sd_bus_call()</function> fails (either because of an internal error or because it
received a D-Bus error reply), <parameter>ret_error</parameter> is initialized to an instance of
<structname>sd_bus_error</structname> describing the error.</para>
<para><function>sd_bus_call_async()</function> is like <function>sd_bus_call()</function> but works
asynchronously. The <parameter>callback</parameter> indicates the function to call when the response
arrives. The <parameter>userdata</parameter> pointer will be passed to the callback function, and may be
chosen freely by the caller. If <parameter>slot</parameter> is not <constant>NULL</constant> and
<function>sd_bus_call_async()</function> succeeds, <parameter>slot</parameter> is set to a slot object
which can be used to cancel the method call at a later time using
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
If <parameter>slot</parameter> is <constant>NULL</constant>, the lifetime of the method call is bound to
the lifetime of the bus object itself, and it cannot be cancelled independently. See
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. <parameter>callback</parameter> is called when a reply arrives with the reply,
<parameter>userdata</parameter> and an <structname>sd_bus_error</structname> output parameter as its
arguments. Unlike <function>sd_bus_call()</function>, the <structname>sd_bus_error</structname> output
parameter passed to the callback will be empty. To determine whether the method call succeeded, use
<citerefentry><refentrytitle>sd_bus_message_is_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
on the reply message passed to the callback instead. If the callback returns zero and the
<structname>sd_bus_error</structname> output parameter is still empty when the callback finishes, other
handlers registered with functions such as
<citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> are
given a chance to process the message. If the callback returns a non-zero value or the
<structname>sd_bus_error</structname> output parameter is not empty when the callback finishes, no
further processing of the message is done. Generally, you want to return zero from the callback to give
other registered handlers a chance to process the reply as well. (Note that the
<structname>sd_bus_error</structname> parameter is an output parameter of the callback function, not an
input parameter; it can be used to propagate errors from the callback handler, it will not receive any
error that was received as method reply.)</para>
<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
new reference.</para>
<para>If <parameter>usec</parameter> is zero, the default D-Bus method call timeout is used. See
<citerefentry><refentrytitle>sd_bus_get_method_call_timeout</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, these functions return a non-negative integer. On failure, they return a
negative errno-style error code.</para>
<refsect2 id='errors'>
<title>Errors</title>
<para>When <function>sd_bus_call()</function> internally receives a D-Bus error reply, it will set
<parameter>ret_error</parameter> if it is not <constant>NULL</constant>, and will return a negative
value mapped from the error reply, see
<citerefentry><refentrytitle>sd_bus_error_get_errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>The input parameter <parameter>m</parameter> is <constant>NULL</constant>.
</para></listitem>
<listitem><para>The input parameter <parameter>m</parameter> is not a D-Bus method call.
To create a new D-Bus method call, use
<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
<listitem><para>The input parameter <parameter>m</parameter> has the
<constant>BUS_MESSAGE_NO_REPLY_EXPECTED</constant> flag set.</para></listitem>
<listitem><para>The input parameter <parameter>error</parameter> is
non-<constant>NULL</constant> but was not set to <constant>SD_BUS_ERROR_NULL</constant>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ECHILD</constant></term>
<listitem><para>The bus connection was allocated in a parent process and is being reused
in a child process after <function>fork()</function>.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOTCONN</constant></term>
<listitem><para>The input parameter <parameter>bus</parameter> is
<constant>NULL</constant> or the bus is not connected.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ECONNRESET</constant></term>
<listitem><para>The bus connection was closed while waiting for the response.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ETIMEDOUT</constant></term>
<listitem><para>A response was not received within the given timeout.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ELOOP</constant></term>
<listitem><para>The message <parameter>m</parameter> is addressed to its own client.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOMEM</constant></term>
<listitem><para>Memory allocation failed.</para></listitem>
</varlistentry>
</variablelist>
</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_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_call_method_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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