man/sd_bus_message_append_array.xml

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  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  25
  26 <refentry id="sd_bus_message_append_array"
  27           xmlns:xi="http://www.w3.org/2001/XInclude">
  28
  29   <refentryinfo>
  30     <title>sd_bus_message_append_array</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>A monkey with a typewriter</contrib>
  36         <firstname>Zbigniew</firstname>
  37         <surname>Jędrzejewski-Szmek</surname>
  38         <email>zbyszek@in.waw.pl</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>sd_bus_message_append_array</refentrytitle>
  45     <manvolnum>3</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>sd_bus_message_append_array</refname>
  50     <refname>sd_bus_message_append_array_memfd</refname>
  51     <refname>sd_bus_message_append_array_iovec</refname>
  52     <refname>sd_bus_message_append_array_space</refname>
  53
  54     <refpurpose>Append an array of fields to a D-Bus
  55     message</refpurpose>
  56   </refnamediv>
  57
  58   <refsynopsisdiv>
  59     <funcsynopsis>
  60       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  61
  62       <funcprototype>
  63         <funcdef>int sd_bus_message_append_array</funcdef>
  64         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  65         <paramdef>char <parameter>type</parameter></paramdef>
  66         <paramdef>char void *<parameter>ptr</parameter></paramdef>
  67         <paramdef>size_t <parameter>size</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>int sd_bus_message_append_array_memfd</funcdef>
  72         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  73         <paramdef>char <parameter>type</parameter></paramdef>
  74         <paramdef>int <parameter>memfd</parameter></paramdef>
  75         <paramdef>uint64_t <parameter>offset</parameter></paramdef>
  76         <paramdef>uint64_t <parameter>size</parameter></paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int sd_bus_message_append_array_iovec</funcdef>
  81         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  82         <paramdef>char <parameter>type</parameter></paramdef>
  83         <paramdef>const struct iovec *<parameter>iov</parameter></paramdef>
  84         <paramdef>unsigned <parameter>n</parameter></paramdef>
  85       </funcprototype>
  86
  87       <funcprototype>
  88         <funcdef>int sd_bus_message_append_array_space</funcdef>
  89         <paramdef>char <parameter>type</parameter></paramdef>
  90         <paramdef>size_t <parameter>size</parameter></paramdef>
  91         <paramdef>void **<parameter>ptr</parameter></paramdef>
  92       </funcprototype>
  93     </funcsynopsis>
  94   </refsynopsisdiv>
  95
  96   <refsect1>
  97     <title>Description</title>
  98
  99     <para>The <function>sd_bus_message_append_array()</function>
 100     function appends an array to a D-Bus message
 101     <parameter>m</parameter>. A container will be opened, the array
 102     contents appended, and the container closed. The parameter
 103     <parameter>type</parameter> determines how the pointer
 104     <parameter>p</parameter> is interpreted.
 105     <parameter>type</parameter> must be one of the "trivial" types
 106     <literal>y</literal>, <literal>n</literal>, <literal>q</literal>,
 107     <literal>i</literal>, <literal>u</literal>, <literal>x</literal>,
 108     <literal>t</literal>, <literal>d</literal> (but not
 109     <literal>b</literal>), as defined by the <ulink
 110     url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic
 111     Types</ulink> section of the D-Bus specification, and listed in
 112     <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 113     Pointer <parameter>p</parameter> must point to an array of size
 114     <parameter>size</parameter> bytes containing items of the
 115     respective type. Size <parameter>size</parameter> must be a
 116     multiple of the size of the type <parameter>type</parameter>. As a
 117     special case, <parameter>p</parameter> may be
 118     <constant>NULL</constant>, if <parameter>size</parameter> is 0.
 119     The memory pointed to by <parameter>p</parameter> is copied into
 120     the memory area containing the message and stays in possession of
 121     the caller. The caller may hence freely change the data after this
 122     call without affecting the message the array was appended
 123     to.</para>
 124
 125     <para>The <function>sd_bus_message_append_array_memfd()</function>
 126     function appends an array of a trivial type to message
 127     <parameter>m</parameter>, similar to
 128     <function>sd_bus_message_append_array()</function>. The contents
 129     of the memory file descriptor <parameter>memfd</parameter>
 130     starting at the specified offset and of the specified size is
 131     used as the contents of the array. The offset and size must be a
 132     multiple of the size of the type
 133     <parameter>type</parameter>. However, as a special exception, if
 134     the offset is specified as zero and the size specified as
 135     UINT64_MAX the full memory file descriptor contents is used. The
 136     memory file descriptor is sealed by this call if it has not been
 137     sealed yet, and cannot be modified after this call. See
 138     <citerefentry
 139     project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 140     for details about memory file descriptors. Appending arrays with
 141     memory file descriptors enables efficient zero-copy data transfer,
 142     as the memory file descriptor may be passed as-is to the
 143     destination, without copying the memory in it to the destination
 144     process. Not all protocol transports support passing memory file
 145     descriptors between participants, in which case this call will
 146     automatically fall back to copying. Also, as memory file
 147     descriptor passing is inefficient for smaller amounts of data,
 148     copying might still be enforced even where memory file descriptor
 149     passing is supported.</para>
 150
 151     <para>The <function>sd_bus_message_append_array_iovec()</function>
 152     function appends an array of a trivial type to the message
 153     <parameter>m</parameter>, similar to
 154     <function>sd_bus_message_append_array()</function>. Contents of
 155     the I/O vector array <parameter>iov</parameter> are used as the
 156     contents of the array. The total size of
 157     <parameter>iov</parameter> payload (the sum of
 158     <structfield>iov_len</structfield> fields) must be a multiple of
 159     the size of the type <parameter>type</parameter>. The
 160     <parameter>iov</parameter> argument must point to
 161     <parameter>n</parameter> I/O vector structures. Each structure may
 162     have the <structname>iov_base</structname> field set, in which
 163     case the memory pointed to will be copied into the message, or
 164     unset (set to zero), in which case a block of zeros of length
 165     <structname>iov_len</structname> bytes will be inserted. The
 166     memory pointed at by <parameter>iov</parameter> may be changed
 167     after this call.</para>
 168
 169     <para>The <function>sd_bus_message_append_array_space()</function>
 170     function appends space for an array of a trivial type to message
 171     <parameter>m</parameter>.  It behaves the same as
 172     <function>sd_bus_message_append_array()</function>, but instead of
 173     copying items to the message, it returns a pointer to the
 174     destination area to the caller in pointer
 175     <parameter>p</parameter>. The caller should subsequently write the
 176     array contents to this memory. Modifications to the memory
 177     pointed to should only occur until the next operation on the bus
 178     message is invoked. Most importantly, the memory should not be
 179     altered anymore when another field has been added to the message
 180     or the message has been sealed.</para>
 181   </refsect1>
 182
 183   <refsect1>
 184     <title>Return Value</title>
 185
 186     <para>On success, these calls return 0 or a positive integer. On
 187     failure, they return a negative errno-style error code.</para>
 188   </refsect1>
 189
 190   <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
 191
 192   <refsect1>
 193     <title>Notes</title>
 194
 195     <para><function>sd_bus_append_array()</function> and other
 196     functions described here are available as a shared library, which
 197     can be compiled and linked to with the
 198     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 199     file.</para>
 200   </refsect1>
 201
 202   <refsect1>
 203     <title>See Also</title>
 204
 205     <para>
 206       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 207       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 208       <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 209       <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 210       <citerefentry project='man-pages'><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 211       <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
 212     </para>
 213   </refsect1>
 214
 215 </refentry>