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209 lines
10 KiB
XML
209 lines
10 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_bus_call"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_call</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_call</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_call</refname>
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<refname>sd_bus_call_async</refname>
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<refpurpose>Invoke a D-Bus method call</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<xi:include href="sd_bus_add_match.xml" xpointer="sd_bus_message_handler_t"/>
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<funcprototype>
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<funcdef>int <function>sd_bus_call</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
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<paramdef>sd_bus_message **<parameter>reply</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_call_async</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_call()</function> takes a complete bus message object and calls the
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corresponding D-Bus method. On success, the response is stored in <parameter>reply</parameter>.
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<parameter>usec</parameter> indicates the timeout in microseconds. If
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<parameter>ret_error</parameter> is not <constant>NULL</constant> and
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<function>sd_bus_call()</function> fails (either because of an internal error or because it
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received a D-Bus error reply), <parameter>ret_error</parameter> is initialized to an instance of
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<structname>sd_bus_error</structname> describing the error.</para>
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<para><function>sd_bus_call_async()</function> is like <function>sd_bus_call()</function> but works
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asynchronously. The <parameter>callback</parameter> indicates the function to call when the response
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arrives. The <parameter>userdata</parameter> pointer will be passed to the callback function, and may be
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chosen freely by the caller. If <parameter>slot</parameter> is not <constant>NULL</constant> and
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<function>sd_bus_call_async()</function> succeeds, <parameter>slot</parameter> is set to a slot object
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which can be used to cancel the method call at a later time using
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<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If <parameter>slot</parameter> is <constant>NULL</constant>, the lifetime of the method call is bound to
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the lifetime of the bus object itself, and it cannot be cancelled independently. See
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<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for details. <parameter>callback</parameter> is called when a reply arrives with the reply,
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<parameter>userdata</parameter> and an <structname>sd_bus_error</structname> output parameter as its
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arguments. Unlike <function>sd_bus_call()</function>, the <structname>sd_bus_error</structname> output
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parameter passed to the callback will be empty. To determine whether the method call succeeded, use
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<citerefentry><refentrytitle>sd_bus_message_is_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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on the reply message passed to the callback instead. If the callback returns zero and the
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<structname>sd_bus_error</structname> output parameter is still empty when the callback finishes, other
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handlers registered with functions such as
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<citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
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<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> are
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given a chance to process the message. If the callback returns a non-zero value or the
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<structname>sd_bus_error</structname> output parameter is not empty when the callback finishes, no
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further processing of the message is done. Generally, you want to return zero from the callback to give
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other registered handlers a chance to process the reply as well. (Note that the
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<structname>sd_bus_error</structname> parameter is an output parameter of the callback function, not an
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input parameter; it can be used to propagate errors from the callback handler, it will not receive any
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error that was received as method reply.)</para>
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<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
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not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
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<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
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new reference.</para>
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<para>If <parameter>usec</parameter> is zero, the default D-Bus method call timeout is used. See
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<citerefentry><refentrytitle>sd_bus_get_method_call_timeout</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return a non-negative integer. On failure, they return a
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negative errno-style error code.</para>
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<refsect2 id='errors'>
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<title>Errors</title>
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<para>When <function>sd_bus_call()</function> internally receives a D-Bus error reply, it will set
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<parameter>ret_error</parameter> if it is not <constant>NULL</constant>, and will return a negative
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value mapped from the error reply, see
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<citerefentry><refentrytitle>sd_bus_error_get_errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem>
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<para>The input parameter <parameter>m</parameter> is <constant>NULL</constant>.
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</para>
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<para>The input parameter <parameter>m</parameter> is not a D-Bus method call.
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To create a new D-Bus method call, use
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<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>The input parameter <parameter>m</parameter> has the
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<constant>BUS_MESSAGE_NO_REPLY_EXPECTED</constant> flag set.</para>
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<para>The input parameter <parameter>error</parameter> is
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non-<constant>NULL</constant> but was not set to <constant>SD_BUS_ERROR_NULL</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The bus connection was allocated in a parent process and is being reused
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in a child process after <function>fork()</function>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOTCONN</constant></term>
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<listitem><para>The input parameter <parameter>bus</parameter> is
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<constant>NULL</constant> or the bus is not connected.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECONNRESET</constant></term>
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<listitem><para>The bus connection was closed while waiting for the response.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ETIMEDOUT</constant></term>
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<listitem><para>A response was not received within the given timeout.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ELOOP</constant></term>
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<listitem><para>The message <parameter>m</parameter> is addressed to its own client.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>History</title>
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<para><function>sd_bus_call()</function> and
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<function>sd_bus_call_async()</function> were added in version 221.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_call_method_async</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_error</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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