-<?xml version='1.0'?> <!--*-nxml-*-->
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
-This file is part of systemd.
+ This file is part of systemd.
-Copyright 2014 Zbigniew Jędrzejewski-Szmek
+ Copyright 2014 Zbigniew Jędrzejewski-Szmek
-systemd is free software; you can redistribute it and/or modify it
-under the terms of the GNU Lesser General Public License as published by
-the Free Software Foundation; either version 2.1 of the License, or
-(at your option) any later version.
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
-systemd is distributed in the hope that it will be useful, but
-WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-Lesser General Public License for more details.
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
-You should have received a copy of the GNU Lesser General Public License
-along with systemd; If not, see <http://www.gnu.org/licenses/>.
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
-<refentry id="sd_bus_message_append_array" conditional="ENABLE_KDBUS"
+<refentry id="sd_bus_message_append_array"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<refname>sd_bus_message_append_array_iovec</refname>
<refname>sd_bus_message_append_array_space</refname>
- <refpurpose>Attach an array of items to a message</refpurpose>
+ <refpurpose>Append an array of fields to a D-Bus
+ message</refpurpose>
</refnamediv>
<refsynopsisdiv>
<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>
</funcprototype>
<funcprototype>
<funcdef>int sd_bus_message_append_array_space</funcdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
- <paramdef>
char void **<parameter>ptr</parameter></paramdef>
+ <paramdef>void **<parameter>ptr</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
- <para>The <function>sd_bus_message_append_array</function> functionc
- appends items to message <parameter>m</parameter> as the single
- array. A container will be opened, items appended, and the
- container closed. Parameter <parameter>type</parameter> determines
- how pointer <parameter>p</parameter> is interpreted.
+ <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 url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic Types</ulink>
- section of the D-Bus specification, and listed in
+ <literal>b</literal>), as defined by the <ulink
+ url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic
+ Types</ulink> section of the D-Bus specification, and listed in
<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Pointer <parameter>p</parameter> must point to an array of size
<parameter>size</parameter> bytes containing items of the
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.
- </para>
-
- <para>The memory pointed at by <parameter>p</parameter> is copied
- into the memory area containing the message and may be changed
- after this call.</para>
-
- <para>The
- <function>sd_bus_message_append_array_memfd</function> function appends
- items to message <parameter>m</parameter>, similarly to
- <function>sd_bus_message_append_array</function>. Contents of the
- memory file descriptor <parameter>memfd</parameter> are used as
- the contents of the array. Their size must be a multiple of the
- size of the type <parameter>type</parameter>.</para>
-
- <para>The descriptor specified with <parameter>memfd</parameter>
- will be sealed and cannot be modified after this call.</para>
-
- <para>The
- <function>sd_bus_message_append_array_iovec</function> function appends
- items to message <parameter>m</parameter>, similarly to
- <function>sd_bus_message_append_array</function>. Contents of the
- iovec <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>.</para>
-
- <para>The <parameter>iov</parameter> argument must point to
- <parameter>n</parameter> <structname>struct iovec</structname>
- 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, in
- which case a block of zeros of length
+ 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
+ to.</para>
+
+ <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
+ <citerefentry
+ project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+ 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 items 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>.
- </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>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, these calls return 0 or a positive integer. On
- failure, they returns a negative errno-style error code.</para>
+ failure, they return a negative errno-style error code.</para>
</refsect1>
<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
<para><function>sd_bus_append_array()</function> and other
functions described here are available as a shared library, which
can be compiled and linked to with the
- <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ <constant>libelogind</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
</para>
</refsect1>
~ianmdlvl / elogind.git / blobdiff