man/sd_bus_add_object_vtable.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_bus_add_object_vtable"
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>sd_bus_add_object_vtable</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>sd_bus_add_object_vtable</refentrytitle>
  16     <manvolnum>3</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>sd_bus_add_object_vtable</refname>
  21     <refname>sd_bus_add_fallback_vtable</refname>
  22     <refname>SD_BUS_VTABLE_START</refname>
  23     <refname>SD_BUS_VTABLE_END</refname>
  24     <refname>SD_BUS_METHOD_WITH_NAMES_OFFSET</refname>
  25     <refname>SD_BUS_METHOD_WITH_NAMES</refname>
  26     <refname>SD_BUS_METHOD_WITH_OFFSET</refname>
  27     <refname>SD_BUS_METHOD</refname>
  28     <refname>SD_BUS_SIGNAL_WITH_NAMES</refname>
  29     <refname>SD_BUS_SIGNAL</refname>
  30     <refname>SD_BUS_WRITABLE_PROPERTY</refname>
  31     <refname>SD_BUS_PROPERTY</refname>
  32     <refname>SD_BUS_PARAM</refname>
  33
  34     <refpurpose>Declare properties and methods for a D-Bus path</refpurpose>
  35   </refnamediv>
  36
  37   <refsynopsisdiv>
  38     <funcsynopsis>
  39       <funcsynopsisinfo>#include &lt;systemd/sd-bus-vtable.h&gt;</funcsynopsisinfo>
  40
  41       <funcprototype>
  42         <funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
  43         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  44         <paramdef>void *<parameter>userdata</parameter></paramdef>
  45         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  46       </funcprototype>
  47
  48       <funcprototype>
  49         <funcdef>typedef int (*<function>sd_bus_property_get_t</function>)</funcdef>
  50         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  51         <paramdef>const char *<parameter>path</parameter></paramdef>
  52         <paramdef>const char *<parameter>interface</parameter></paramdef>
  53         <paramdef>const char *<parameter>property</parameter></paramdef>
  54         <paramdef>sd_bus_message *<parameter>reply</parameter></paramdef>
  55         <paramdef>void *<parameter>userdata</parameter></paramdef>
  56         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  57       </funcprototype>
  58
  59       <funcprototype>
  60         <funcdef>typedef int (*<function>sd_bus_property_set_t</function>)</funcdef>
  61         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  62         <paramdef>const char *<parameter>path</parameter></paramdef>
  63         <paramdef>const char *<parameter>interface</parameter></paramdef>
  64         <paramdef>const char *<parameter>property</parameter></paramdef>
  65         <paramdef>sd_bus_message *<parameter>value</parameter></paramdef>
  66         <paramdef>void *<parameter>userdata</parameter></paramdef>
  67         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>typedef int (*<function>sd_bus_object_find_t</function>)</funcdef>
  72         <paramdef>const char *<parameter>path</parameter></paramdef>
  73         <paramdef>const char *<parameter>interface</parameter></paramdef>
  74         <paramdef>void *<parameter>userdata</parameter></paramdef>
  75         <paramdef>void **<parameter>ret_found</parameter></paramdef>
  76         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int <function>sd_bus_add_object_vtable</function></funcdef>
  81         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  82         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  83         <paramdef>const char *<parameter>path</parameter></paramdef>
  84         <paramdef>const char *<parameter>interface</parameter></paramdef>
  85         <paramdef>const sd_bus_vtable *<parameter>vtable</parameter></paramdef>
  86         <paramdef>void *<parameter>userdata</parameter></paramdef>
  87       </funcprototype>
  88
  89       <funcprototype>
  90         <funcdef>int <function>sd_bus_add_fallback_vtable</function></funcdef>
  91         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  92         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  93         <paramdef>const char *<parameter>prefix</parameter></paramdef>
  94         <paramdef>const char *<parameter>interface</parameter></paramdef>
  95         <paramdef>const sd_bus_vtable *<parameter>vtable</parameter></paramdef>
  96         <paramdef>sd_bus_object_find_t <parameter>find</parameter></paramdef>
  97         <paramdef>void *<parameter>userdata</parameter></paramdef>
  98       </funcprototype>
  99
 100       <para>
 101         <constant>SD_BUS_VTABLE_START(<replaceable>flags</replaceable>)</constant>
 102       </para>
 103       <para>
 104         <constant>SD_BUS_VTABLE_END</constant>
 105       </para>
 106       <para>
 107         <constant>SD_BUS_METHOD_WITH_NAMES_OFFSET(
 108         <replaceable>member</replaceable>,
 109         <replaceable>signature</replaceable>,
 110         <replaceable>in_names</replaceable>,
 111         <replaceable>result</replaceable>,
 112         <replaceable>out_names</replaceable>,
 113         <replaceable>handler</replaceable>,
 114         <replaceable>offset</replaceable>,
 115         <replaceable>flags</replaceable>)
 116         </constant>
 117       </para>
 118       <para>
 119         <constant>SD_BUS_METHOD_WITH_NAMES(
 120         <replaceable>member</replaceable>,
 121         <replaceable>signature</replaceable>,
 122         <replaceable>in_names</replaceable>,
 123         <replaceable>result</replaceable>,
 124         <replaceable>out_names</replaceable>,
 125         <replaceable>handler</replaceable>,
 126         <replaceable>flags</replaceable>)
 127         </constant>
 128       </para>
 129       <para>
 130         <constant>SD_BUS_METHOD_WITH_OFFSET(
 131         <replaceable>member</replaceable>,
 132         <replaceable>signature</replaceable>,
 133         <replaceable>result</replaceable>,
 134         <replaceable>handler</replaceable>,
 135         <replaceable>offset</replaceable>,
 136         <replaceable>flags</replaceable>)
 137         </constant>
 138       </para>
 139       <para>
 140         <constant>SD_BUS_METHOD(
 141         <replaceable>member</replaceable>,
 142         <replaceable>signature</replaceable>,
 143         <replaceable>result</replaceable>,
 144         <replaceable>handler</replaceable>,
 145         <replaceable>flags</replaceable>)
 146         </constant>
 147       </para>
 148       <para>
 149         <constant>SD_BUS_SIGNAL_WITH_NAMES(
 150         <replaceable>member</replaceable>,
 151         <replaceable>signature</replaceable>,
 152         <replaceable>names</replaceable>,
 153         <replaceable>flags</replaceable>)
 154         </constant>
 155       </para>
 156       <para>
 157         <constant>SD_BUS_SIGNAL(
 158         <replaceable>member</replaceable>,
 159         <replaceable>signature</replaceable>,
 160         <replaceable>flags</replaceable>)
 161         </constant>
 162       </para>
 163       <para>
 164         <constant>SD_BUS_WRITABLE_PROPERTY(
 165         <replaceable>member</replaceable>,
 166         <replaceable>signature</replaceable>,
 167         <replaceable>get</replaceable>,
 168         <replaceable>set</replaceable>,
 169         <replaceable>offset</replaceable>,
 170         <replaceable>flags</replaceable>)
 171         </constant>
 172       </para>
 173       <para>
 174         <constant>SD_BUS_PROPERTY(
 175         <replaceable>member</replaceable>,
 176         <replaceable>signature</replaceable>,
 177         <replaceable>get</replaceable>,
 178         <replaceable>offset</replaceable>,
 179         <replaceable>flags</replaceable>)
 180         </constant>
 181       </para>
 182       <para>
 183         <constant>SD_BUS_PARAM(<replaceable>name</replaceable>)</constant>
 184       </para>
 185     </funcsynopsis>
 186   </refsynopsisdiv>
 187
 188   <refsect1>
 189     <title>Description</title>
 190
 191     <para><function>sd_bus_add_object_vtable()</function> is used to declare attributes for the path
 192     object path <parameter>path</parameter> connected to the bus connection
 193     <parameter>bus</parameter> under the interface <parameter>interface</parameter>. The table
 194     <parameter>vtable</parameter> may contain property declarations using
 195     <constant>SD_BUS_PROPERTY()</constant> or <constant>SD_BUS_WRITABLE_PROPERTY()</constant>,
 196     method declarations using <constant>SD_BUS_METHOD()</constant>,
 197     <constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
 198     <constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, or
 199     <constant>SD_BUS_METHOD_WITH_NAMES_OFFSET()</constant>, and signal declarations using
 200     <constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> or <constant>SD_BUS_SIGNAL()</constant>, see
 201     below. The <replaceable>userdata</replaceable> parameter contains a pointer that will be passed
 202     to various callback functions. It may be specified as <constant>NULL</constant> if no value is
 203     necessary.</para>
 204
 205     <para><function>sd_bus_add_fallback_vtable()</function> is similar to
 206     <function>sd_bus_add_object_vtable()</function>, but is used to register "fallback" attributes.
 207     When looking for an attribute declaration, bus object paths registered with
 208     <function>sd_bus_add_object_vtable()</function> are checked first. If no match is found, the
 209     fallback vtables are checked for each prefix of the bus object path, i.e. with the last
 210     slash-separated components successively removed. This allows the vtable to be used for an
 211     arbitrary number of dynamically created objects.</para>
 212
 213     <para>Parameter <replaceable>find</replaceable> is a function which is used to locate the target
 214     object based on the bus object path <replaceable>path</replaceable>. It must return
 215     <constant>1</constant> and set the <parameter>ret_found</parameter> output parameter if the
 216     object is found, return <constant>0</constant> if the object was not found, and return a
 217     negative errno-style error code or initialize the error structure
 218     <replaceable>ret_error</replaceable> on error. The pointer passed in
 219     <parameter>ret_found</parameter> will be used as the <parameter>userdata</parameter> parameter
 220     for the callback functions (offset by the <parameter>offset</parameter> offsets as specified in
 221     the vtable entries).</para>
 222
 223     <para>For both functions, a match slot is created internally. If the output parameter
 224     <replaceable>slot</replaceable> is <constant>NULL</constant>, a "floating" slot object is
 225     created, see
 226     <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 227     Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot
 228     object should be dropped when the vtable is not needed anymore, see
 229     <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 230     </para>
 231
 232     <refsect2>
 233       <title>The <structname>sd_bus_vtable</structname> array</title>
 234
 235       <para>The array consists of the structures of type <structname>sd_bus_vtable</structname>, but it
 236       should never be filled in manually, but through one of the following macros:</para>
 237
 238       <variablelist>
 239         <varlistentry>
 240           <term><constant>SD_BUS_VTABLE_START()</constant></term>
 241           <term><constant>SD_BUS_VTABLE_END</constant></term>
 242
 243           <listitem><para>Those must always be the first and last element.</para></listitem>
 244         </varlistentry>
 245
 246         <varlistentry>
 247           <term><constant>SD_BUS_METHOD_WITH_NAMES_OFFSET()</constant></term>
 248           <term><constant>SD_BUS_METHOD_WITH_NAMES()</constant></term>
 249           <term><constant>SD_BUS_METHOD_WITH_OFFSET()</constant></term>
 250           <term><constant>SD_BUS_METHOD()</constant></term>
 251
 252           <listitem><para>Declare a D-Bus method with the name <replaceable>member</replaceable>,
 253           parameter signature <replaceable>signature</replaceable>, result signature
 254           <replaceable>result</replaceable>. Parameters <replaceable>in_names</replaceable> and
 255           <replaceable>out_names</replaceable> specify the argument names of the input and output
 256           arguments in the function signature. The handler function
 257           <replaceable>handler</replaceable> must be of type
 258           <function>sd_bus_message_handler_t</function>. It will be called to handle the incoming
 259           messages that call this method. It receives a pointer that is the
 260           <replaceable>userdata</replaceable> parameter passed to the registration function offset
 261           by <replaceable>offset</replaceable> bytes. This may be used to pass pointers to different
 262           fields in the same data structure to different methods in the same vtable.
 263           <replaceable>in_names</replaceable> and <replaceable>out_names</replaceable> should be
 264           created using the <constant>SD_BUS_PARAM()</constant> macro, see below. Parameter
 265           <replaceable>flags</replaceable> is a combination of flags, see below.</para>
 266
 267           <para><constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
 268           <constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, and <constant>SD_BUS_METHOD()</constant>
 269           are variants which specify zero offset (<replaceable>userdata</replaceable> parameter is
 270           passed with no change), leave the names unset (i.e. no parameter names), or both.</para>
 271           </listitem>
 272         </varlistentry>
 273
 274         <varlistentry>
 275           <term><constant>SD_BUS_SIGNAL_WITH_NAMES()</constant></term>
 276           <term><constant>SD_BUS_SIGNAL()</constant></term>
 277
 278           <listitem><para>Declare a D-Bus signal with the name <replaceable>member</replaceable>,
 279           parameter signature <replaceable>signature</replaceable>, and argument names
 280           <replaceable>names</replaceable>. <replaceable>names</replaceable> should be
 281           created using the <constant>SD_BUS_PARAM()</constant> macro, see below.
 282           Parameter <replaceable>flags</replaceable> is a combination of flags, see below.
 283           </para>
 284
 285           <para>Equivalent to <constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> with the
 286           <replaceable>names</replaceable> parameter unset (i.e. no parameter names).</para>
 287           </listitem>
 288         </varlistentry>
 289
 290         <varlistentry>
 291           <term><constant>SD_BUS_WRITABLE_PROPERTY()</constant></term>
 292           <term><constant>SD_BUS_PROPERTY()</constant></term>
 293
 294           <listitem><para>Declare a D-Bus property with the name <replaceable>member</replaceable>
 295           and value signature <replaceable>signature</replaceable>. Parameters
 296           <replaceable>get</replaceable> and <replaceable>set</replaceable> are the getter and
 297           setter methods. They are called with a pointer that is the
 298           <replaceable>userdata</replaceable> parameter passed to the registration function offset
 299           by <replaceable>offset</replaceable> bytes. This may be used pass pointers to different
 300           fields in the same data structure to different setters and getters in the same vtable.
 301           Parameter <replaceable>flags</replaceable> is a combination of flags, see below.</para>
 302
 303           <para>The setter and getter methods may be omitted (specified as
 304           <constant>NULL</constant>), if the property has one of the basic types or
 305           <literal>as</literal> in case of read-only properties. In those cases, the
 306           <replaceable>userdata</replaceable> and <replaceable>offset</replaceable> parameters must
 307           together point to valid variable of the corresponding type. A default setter and getters
 308           will be provided, which simply copy the argument between this variable and the message.
 309           </para>
 310
 311           <para><constant>SD_BUS_PROPERTY()</constant> is used to define a read-only property.
 312           </para></listitem>
 313         </varlistentry>
 314
 315         <varlistentry>
 316           <term><constant>SD_BUS_PARAM()</constant></term>
 317           <listitem><para>Parameter names should be wrapped in this macro, see the example below.
 318           </para></listitem>
 319         </varlistentry>
 320       </variablelist>
 321     </refsect2>
 322
 323     <refsect2>
 324       <title>Flags</title>
 325
 326       <para>The <replaceable>flags</replaceable> parameter is used to specify a combination of
 327       <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format">D-Bus annotations</ulink>.
 328       </para>
 329
 330       <variablelist>
 331         <varlistentry>
 332           <term><constant>SD_BUS_VTABLE_DEPRECATED</constant></term>
 333
 334           <listitem><para>Mark this vtable entry as deprecated using the
 335           <constant>org.freedesktop.DBus.Deprecated</constant> annotation in introspection data. If
 336           specified for <constant>SD_BUS_VTABLE_START()</constant>, the annotation is applied to the
 337           enclosing interface.</para></listitem>
 338         </varlistentry>
 339
 340         <varlistentry>
 341           <term><constant>SD_BUS_VTABLE_HIDDEN</constant></term>
 342
 343           <listitem><para>Make this vtable entry hidden. It will not be shown in introspection data.
 344           If specified for <constant>SD_BUS_VTABLE_START()</constant>, all entries in the array are
 345           hidden.</para></listitem>
 346         </varlistentry>
 347
 348         <varlistentry>
 349           <term><constant>SD_BUS_VTABLE_UNPRIVILEGED</constant></term>
 350
 351           <listitem><para>Mark this vtable entry as unprivileged. If not specified, the
 352           <constant>org.freedesktop.systemd1.Privileged</constant> annotation with value
 353           <literal>true</literal> will be shown in introspection data.</para></listitem>
 354         </varlistentry>
 355
 356         <varlistentry>
 357           <term><constant>SD_BUS_VTABLE_METHOD_NO_REPLY</constant></term>
 358
 359           <listitem><para>Mark his vtable entry as a method that will not return a reply using the
 360           <constant>org.freedesktop.DBus.Method.NoReply</constant> annotation in introspection data.
 361           </para></listitem>
 362         </varlistentry>
 363
 364         <varlistentry>
 365           <term><constant>SD_BUS_VTABLE_PROPERTY_CONST</constant></term>
 366           <term><constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant></term>
 367           <term><constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant></term>
 368
 369           <listitem><para>Those three flags correspond to different values of the
 370           <constant>org.freedesktop.DBus.Property.EmitsChangedSignal</constant> annotation, which
 371           specifies whether the
 372           <constant>org.freedesktop.DBus.Properties.PropertiesChanged</constant> signal is emitted
 373           whenever the property changes. <constant>SD_BUS_VTABLE_PROPERTY_CONST</constant>
 374           corresponds to <constant>const</constant> and means that the property never changes during
 375           the lifetime of the object it belongs to, so no signal needs to be emitted.
 376           <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant> corresponds to
 377           <constant>true</constant> and means that the signal is emitted.
 378           <constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant> corresponds to
 379           <constant>invalidates</constant> and means that the signal is emitted, but the value is
 380           not included in the signal.</para></listitem>
 381         </varlistentry>
 382
 383         <varlistentry>
 384           <term><constant>SD_BUS_VTABLE_PROPERTY_EXPLICIT</constant></term>
 385
 386           <listitem><para>Mark this vtable property entry as requiring explicit request to for the
 387           value to be shown (generally because the value is large or slow to calculate). This entry
 388           cannot be combined with <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant>, and will
 389           not be shown in property listings by default (e.g. <command>busctl introspect</command>).
 390           This corresponds to the <constant>org.freedesktop.systemd1.Explicit</constant> annotation
 391           in introspection data.</para></listitem>
 392         </varlistentry>
 393       </variablelist>
 394     </refsect2>
 395   </refsect1>
 396
 397   <refsect1>
 398     <title>Examples</title>
 399
 400     <example>
 401       <title>Create a simple listener on the bus</title>
 402
 403       <programlisting><xi:include href="vtable-example.c" parse="text" /></programlisting>
 404
 405       <para>This creates a simple client on the bus (the user bus, when run as normal user). We may
 406       use the D-Bus <constant>org.freedesktop.DBus.Introspectable.Introspect</constant> call to
 407       acquire the XML description of the interface:</para>
 408
 409       <programlisting><xi:include href="vtable-example.xml" parse="text" /></programlisting>
 410     </example>
 411   </refsect1>
 412
 413   <refsect1>
 414     <title>Return Value</title>
 415
 416     <para>On success, <function>sd_bus_add_object_vtable</function> and
 417     <function>sd_bus_add_fallback_vtable</function> calls return 0 or a positive integer. On
 418     failure, they return a negative errno-style error code.</para>
 419
 420     <refsect2>
 421       <title>Errors</title>
 422
 423       <para>Returned errors may indicate the following problems:</para>
 424
 425       <variablelist>
 426         <varlistentry>
 427           <term><constant>-EINVAL</constant></term>
 428
 429           <listitem><para>One of the required parameters is <constant>NULL</constant> or invalid. A
 430           reserved D-Bus interface was passed as the <replaceable>interface</replaceable> parameter.
 431           </para></listitem>
 432         </varlistentry>
 433
 434         <varlistentry>
 435           <term><constant>-ENOPKG</constant></term>
 436
 437           <listitem><para>The bus cannot be resolved.</para></listitem>
 438         </varlistentry>
 439
 440         <varlistentry>
 441           <term><constant>-ECHILD</constant></term>
 442
 443           <listitem><para>The bus was created in a different process.</para></listitem>
 444         </varlistentry>
 445
 446         <varlistentry>
 447           <term><constant>-ENOMEM</constant></term>
 448
 449           <listitem><para>Memory allocation failed.</para></listitem>
 450         </varlistentry>
 451
 452         <varlistentry>
 453           <term><constant>-EPROTOTYPE</constant></term>
 454
 455           <listitem><para><function>sd_bus_add_object_vtable</function> and
 456           <function>sd_bus_add_fallback_vtable</function> have been both called for the same bus
 457           object path, which is not allowed.</para></listitem>
 458         </varlistentry>
 459
 460         <varlistentry>
 461           <term><constant>-EEXIST</constant></term>
 462
 463           <listitem><para>This vtable has already been registered for this
 464           <replaceable>interface</replaceable> and <replaceable>path</replaceable>.
 465           </para></listitem>
 466         </varlistentry>
 467       </variablelist>
 468     </refsect2>
 469   </refsect1>
 470
 471   <xi:include href="libsystemd-pkgconfig.xml" />
 472
 473   <refsect1>
 474     <title>See Also</title>
 475
 476     <para>
 477       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 478       <citerefentry><refentrytitle>busctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 479     </para>
 480   </refsect1>
 481 </refentry>