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216 lines
9.7 KiB
XML
216 lines
9.7 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2014 Zbigniew Jędrzejewski-Szmek
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_bus_message_append_array"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_message_append_array</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>A monkey with a typewriter</contrib>
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<firstname>Zbigniew</firstname>
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<surname>Jędrzejewski-Szmek</surname>
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<email>zbyszek@in.waw.pl</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_message_append_array</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_message_append_array</refname>
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<refname>sd_bus_message_append_array_memfd</refname>
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<refname>sd_bus_message_append_array_iovec</refname>
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<refname>sd_bus_message_append_array_space</refname>
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<refpurpose>Append an array of fields to a D-Bus
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message</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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<funcprototype>
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<funcdef>int sd_bus_message_append_array</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>char void *<parameter>ptr</parameter></paramdef>
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<paramdef>size_t <parameter>size</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_append_array_memfd</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>int <parameter>memfd</parameter></paramdef>
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<paramdef>uint64_t <parameter>offset</parameter></paramdef>
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<paramdef>uint64_t <parameter>size</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_append_array_iovec</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
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<paramdef>unsigned <parameter>n</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_append_array_space</funcdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>size_t <parameter>size</parameter></paramdef>
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<paramdef>void **<parameter>ptr</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>The <function>sd_bus_message_append_array()</function>
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function appends an array to a D-Bus message
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<parameter>m</parameter>. A container will be opened, the array
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contents appended, and the container closed. The parameter
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<parameter>type</parameter> determines how the pointer
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<parameter>p</parameter> is interpreted.
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<parameter>type</parameter> must be one of the "trivial" types
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<literal>y</literal>, <literal>n</literal>, <literal>q</literal>,
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<literal>i</literal>, <literal>u</literal>, <literal>x</literal>,
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<literal>t</literal>, <literal>d</literal> (but not
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<literal>b</literal>), as defined by the <ulink
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url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic
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Types</ulink> section of the D-Bus specification, and listed in
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<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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Pointer <parameter>p</parameter> must point to an array of size
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<parameter>size</parameter> bytes containing items of the
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respective type. Size <parameter>size</parameter> must be a
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multiple of the size of the type <parameter>type</parameter>. As a
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special case, <parameter>p</parameter> may be
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<constant>NULL</constant>, if <parameter>size</parameter> is 0.
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The memory pointed to by <parameter>p</parameter> is copied into
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the memory area containing the message and stays in possession of
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the caller. The caller may hence freely change the data after this
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call without affecting the message the array was appended
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to.</para>
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<para>The <function>sd_bus_message_append_array_memfd()</function>
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function appends an array of a trivial type to message
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<parameter>m</parameter>, similar to
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<function>sd_bus_message_append_array()</function>. The contents
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of the memory file descriptor <parameter>memfd</parameter>
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starting at the specified offset and of the specified size is
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used as the contents of the array. The offset and size must be a
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multiple of the size of the type
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<parameter>type</parameter>. However, as a special exception, if
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the offset is specified as zero and the size specified as
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UINT64_MAX the full memory file descriptor contents is used. The
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memory file descriptor is sealed by this call if it has not been
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sealed yet, and cannot be modified after this call. See
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<citerefentry
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project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for details about memory file descriptors. Appending arrays with
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memory file descriptors enables efficient zero-copy data transfer,
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as the memory file descriptor may be passed as-is to the
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destination, without copying the memory in it to the destination
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process. Not all protocol transports support passing memory file
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descriptors between participants, in which case this call will
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automatically fall back to copying. Also, as memory file
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descriptor passing is inefficient for smaller amounts of data,
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copying might still be enforced even where memory file descriptor
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passing is supported.</para>
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<para>The <function>sd_bus_message_append_array_iovec()</function>
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function appends an array of a trivial type to the message
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<parameter>m</parameter>, similar to
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<function>sd_bus_message_append_array()</function>. Contents of
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the I/O vector array <parameter>iov</parameter> are used as the
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contents of the array. The total size of
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<parameter>iov</parameter> payload (the sum of
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<structfield>iov_len</structfield> fields) must be a multiple of
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the size of the type <parameter>type</parameter>. The
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<parameter>iov</parameter> argument must point to
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<parameter>n</parameter> I/O vector structures. Each structure may
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have the <structname>iov_base</structname> field set, in which
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case the memory pointed to will be copied into the message, or
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unset (set to zero), in which case a block of zeros of length
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<structname>iov_len</structname> bytes will be inserted. The
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memory pointed at by <parameter>iov</parameter> may be changed
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after this call.</para>
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<para>The <function>sd_bus_message_append_array_space()</function>
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function appends space for an array of a trivial type to message
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<parameter>m</parameter>. It behaves the same as
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<function>sd_bus_message_append_array()</function>, but instead of
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copying items to the message, it returns a pointer to the
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destination area to the caller in pointer
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<parameter>p</parameter>. The caller should subsequently write the
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array contents to this memory. Modifications to the memory
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pointed to should only occur until the next operation on the bus
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message is invoked. Most importantly, the memory should not be
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altered anymore when another field has been added to the message
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or the message has been sealed.</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 calls return 0 or a positive integer. On
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failure, they return a negative errno-style error code.</para>
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</refsect1>
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<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
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<refsect1>
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<title>Notes</title>
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<para><function>sd_bus_append_array()</function> and other
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functions described here are available as a shared library, which
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can be compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
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</para>
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</refsect1>
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</refentry>
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