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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_bus_message_append_array"
<refpurpose>Append an array of fields to a D-Bus
<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
<funcdef>int sd_bus_message_append_array</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<funcdef>int sd_bus_message_append_array_memfd</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>int <parameter>memfd</parameter></paramdef>
<paramdef>uint64_t <parameter>offset</parameter></paramdef>
<paramdef>uint64_t <parameter>size</parameter></paramdef>
<funcdef>int sd_bus_message_append_array_iovec</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
<paramdef>unsigned <parameter>n</parameter></paramdef>
<funcdef>int sd_bus_message_append_array_space</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>void **<parameter>ptr</parameter></paramdef>
<para>The <function>sd_bus_message_append_array()</function>
function appends an array to a D-Bus message
<parameter>m</parameter>. A container will be opened, the array
contents appended, and the container closed. The parameter
<parameter>type</parameter> determines how the pointer
<parameter>p</parameter> is interpreted.
<parameter>type</parameter> must be one of the "trivial" types
<literal>y</literal>, <literal>n</literal>, <literal>q</literal>,
<literal>i</literal>, <literal>u</literal>, <literal>x</literal>,
<literal>t</literal>, <literal>d</literal> (but not
<literal>b</literal>), as defined by the <ulink
Types</ulink> section of the D-Bus specification, and listed in
Pointer <parameter>p</parameter> must point to an array of size
<parameter>size</parameter> bytes containing items of the
respective type. Size <parameter>size</parameter> must be a
multiple of the size of the type <parameter>type</parameter>. As a
special case, <parameter>p</parameter> may be
<constant>NULL</constant>, if <parameter>size</parameter> is 0.
The memory pointed to by <parameter>p</parameter> is copied into
the memory area containing the message and stays in possession of
the caller. The caller may hence freely change the data after this
call without affecting the message the array was appended
<para>The <function>sd_bus_message_append_array_memfd()</function>
function appends an array of a trivial type to message
<parameter>m</parameter>, similar to
<function>sd_bus_message_append_array()</function>. The contents
of the memory file descriptor <parameter>memfd</parameter>
starting at the specified offset and of the specified size is
used as the contents of the array. The offset and size must be a
multiple of the size of the type
<parameter>type</parameter>. However, as a special exception, if
the offset is specified as zero and the size specified as
UINT64_MAX the full memory file descriptor contents is used. The
memory file descriptor is sealed by this call if it has not been
sealed yet, and cannot be modified after this call. See
for details about memory file descriptors. Appending arrays with
memory file descriptors enables efficient zero-copy data transfer,
as the memory file descriptor may be passed as-is to the
destination, without copying the memory in it to the destination
process. Not all protocol transports support passing memory file
descriptors between participants, in which case this call will
automatically fall back to copying. Also, as memory file
descriptor passing is inefficient for smaller amounts of data,
copying might still be enforced even where memory file descriptor
passing is supported.</para>
<para>The <function>sd_bus_message_append_array_iovec()</function>
function appends an array of a trivial type to the message
<parameter>m</parameter>, similar to
<function>sd_bus_message_append_array()</function>. Contents of
the I/O vector array <parameter>iov</parameter> are used as the
contents of the array. The total size of
<parameter>iov</parameter> payload (the sum of
<structfield>iov_len</structfield> fields) must be a multiple of
the size of the type <parameter>type</parameter>. The
<parameter>iov</parameter> argument must point to
<parameter>n</parameter> I/O vector structures. Each structure may
have the <structname>iov_base</structname> field set, in which
case the memory pointed to will be copied into the message, or
unset (set to zero), in which case a block of zeros of length
<structname>iov_len</structname> bytes will be inserted. The
memory pointed at by <parameter>iov</parameter> may be changed
after this call.</para>
<para>The <function>sd_bus_message_append_array_space()</function>
function appends space for an array of a trivial type to message
<parameter>m</parameter>. It behaves the same as
<function>sd_bus_message_append_array()</function>, but instead of
copying items to the message, it returns a pointer to the
destination area to the caller in pointer
<parameter>p</parameter>. The caller should subsequently write the
array contents to this memory. Modifications to the memory
pointed to should only occur until the next operation on the bus
message is invoked. Most importantly, the memory should not be
altered anymore when another field has been added to the message
or the message has been sealed.</para>
<title>Return Value</title>
<para>On success, these calls return 0 or a positive integer. On failure, they return a negative
errno-style error code.</para>
<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
<xi:include href="libsystemd-pkgconfig.xml" />
<title>See Also</title>
<citerefentry project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<ulink url="">The D-Bus specification</ulink>