man/sd_bus_add_object_vtable.xml

<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->

<refentry id="sd_bus_add_object_vtable"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_bus_add_object_vtable</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_add_object_vtable</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_add_object_vtable</refname>
    <refname>sd_bus_add_fallback_vtable</refname>
    <refname>SD_BUS_VTABLE_START</refname>
    <refname>SD_BUS_VTABLE_END</refname>
    <refname>SD_BUS_METHOD_WITH_NAMES_OFFSET</refname>
    <refname>SD_BUS_METHOD_WITH_NAMES</refname>
    <refname>SD_BUS_METHOD_WITH_OFFSET</refname>
    <refname>SD_BUS_METHOD</refname>
    <refname>SD_BUS_SIGNAL_WITH_NAMES</refname>
    <refname>SD_BUS_SIGNAL</refname>
    <refname>SD_BUS_WRITABLE_PROPERTY</refname>
    <refname>SD_BUS_PROPERTY</refname>
    <refname>SD_BUS_PARAM</refname>

    <refpurpose>Declare properties and methods for a D-Bus path</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-bus-vtable.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
        <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_bus_property_get_t</function>)</funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>const char *<parameter>property</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>reply</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
        <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_bus_property_set_t</function>)</funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>const char *<parameter>property</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>value</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
        <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_bus_object_find_t</function>)</funcdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
        <paramdef>void **<parameter>ret_found</parameter></paramdef>
        <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_add_object_vtable</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>const sd_bus_vtable *<parameter>vtable</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_add_fallback_vtable</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
        <paramdef>const char *<parameter>prefix</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>const sd_bus_vtable *<parameter>vtable</parameter></paramdef>
        <paramdef>sd_bus_object_find_t <parameter>find</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <para>
        <constant>SD_BUS_VTABLE_START(<replaceable>flags</replaceable>)</constant>
      </para>
      <para>
        <constant>SD_BUS_VTABLE_END</constant>
      </para>
      <para>
        <constant>SD_BUS_METHOD_WITH_NAMES_OFFSET(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>in_names</replaceable>,
        <replaceable>result</replaceable>,
        <replaceable>out_names</replaceable>,
        <replaceable>handler</replaceable>,
        <replaceable>offset</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_METHOD_WITH_NAMES(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>in_names</replaceable>,
        <replaceable>result</replaceable>,
        <replaceable>out_names</replaceable>,
        <replaceable>handler</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_METHOD_WITH_OFFSET(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>result</replaceable>,
        <replaceable>handler</replaceable>,
        <replaceable>offset</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_METHOD(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>result</replaceable>,
        <replaceable>handler</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_SIGNAL_WITH_NAMES(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>names</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_SIGNAL(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_WRITABLE_PROPERTY(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>get</replaceable>,
        <replaceable>set</replaceable>,
        <replaceable>offset</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_PROPERTY(
        <replaceable>member</replaceable>,
        <replaceable>signature</replaceable>,
        <replaceable>get</replaceable>,
        <replaceable>offset</replaceable>,
        <replaceable>flags</replaceable>)
        </constant>
      </para>
      <para>
        <constant>SD_BUS_PARAM(<replaceable>name</replaceable>)</constant>
      </para>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_add_object_vtable()</function> is used to declare attributes for the path object
    path <parameter>path</parameter> connected to the bus connection <parameter>bus</parameter> under the
    interface <parameter>interface</parameter>. The table <parameter>vtable</parameter> may contain property
    declarations using <constant>SD_BUS_PROPERTY()</constant> or
    <constant>SD_BUS_WRITABLE_PROPERTY()</constant>, method declarations using
    <constant>SD_BUS_METHOD()</constant>, <constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
    <constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, or
    <constant>SD_BUS_METHOD_WITH_NAMES_OFFSET()</constant>, and signal declarations using
    <constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> or <constant>SD_BUS_SIGNAL()</constant>, see below. The
    <replaceable>userdata</replaceable> parameter contains a pointer that will be passed to various callback
    functions. It may be specified as <constant>NULL</constant> if no value is necessary.</para>

    <para><function>sd_bus_add_fallback_vtable()</function> is similar to
    <function>sd_bus_add_object_vtable()</function>, but is used to register "fallback" attributes. When
    looking for an attribute declaration, bus object paths registered with
    <function>sd_bus_add_object_vtable()</function> are checked first. If no match is found, the fallback
    vtables are checked for each prefix of the bus object path, i.e. with the last slash-separated components
    successively removed. This allows the vtable to be used for an arbitrary number of dynamically created
    objects.</para>

    <para>Parameter <replaceable>find</replaceable> is a function which is used to locate the target object
    based on the bus object path <replaceable>path</replaceable>. It must return <constant>1</constant> and
    set the <parameter>ret_found</parameter> output parameter if the object is found, return
    <constant>0</constant> if the object was not found, and return a negative errno-style error code or
    initialize the error structure <replaceable>ret_error</replaceable> on error. The pointer passed in
    <parameter>ret_found</parameter> will be used as the <parameter>userdata</parameter> parameter for the
    callback functions (offset by the <parameter>offset</parameter> offsets as specified in the vtable
    entries).</para>

    <para>For both functions, a match slot is created internally. If the output parameter
    <replaceable>slot</replaceable> is <constant>NULL</constant>, a "floating" slot object is created, see
    <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot object
    should be dropped when the vtable is not needed anymore, see
    <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>

    <refsect2>
      <title>The <structname>sd_bus_vtable</structname> array</title>

      <para>The array consists of the structures of type <structname>sd_bus_vtable</structname>, but it
      should never be filled in manually, but through one of the following macros:</para>

      <variablelist>
        <varlistentry>
          <term><constant>SD_BUS_VTABLE_START()</constant></term>
          <term><constant>SD_BUS_VTABLE_END</constant></term>

          <listitem><para>Those must always be the first and last element.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_METHOD_WITH_NAMES_OFFSET()</constant></term>
          <term><constant>SD_BUS_METHOD_WITH_NAMES()</constant></term>
          <term><constant>SD_BUS_METHOD_WITH_OFFSET()</constant></term>
          <term><constant>SD_BUS_METHOD()</constant></term>

          <listitem><para>Declare a D-Bus method with the name <replaceable>member</replaceable>, parameter
          signature <replaceable>signature</replaceable>, result signature <replaceable>result</replaceable>.
          Parameters <replaceable>in_names</replaceable> and <replaceable>out_names</replaceable> specify the
          argument names of the input and output arguments in the function signature. The handler function
          <replaceable>handler</replaceable> must be of type <function>sd_bus_message_handler_t</function>.
          It will be called to handle the incoming messages that call this method. It receives a pointer that
          is the <replaceable>userdata</replaceable> parameter passed to the registration function offset by
          <replaceable>offset</replaceable> bytes. This may be used to pass pointers to different fields in
          the same data structure to different methods in the same
          vtable. <replaceable>in_names</replaceable> and <replaceable>out_names</replaceable> should be
          created using the <constant>SD_BUS_PARAM()</constant> macro, see below. Parameter
          <replaceable>flags</replaceable> is a combination of flags, see below.</para>

          <para><constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
          <constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, and <constant>SD_BUS_METHOD()</constant> are
          variants which specify zero offset (<replaceable>userdata</replaceable> parameter is passed with
          no change), leave the names unset (i.e. no parameter names), or both.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_SIGNAL_WITH_NAMES()</constant></term>
          <term><constant>SD_BUS_SIGNAL()</constant></term>

          <listitem><para>Declare a D-Bus signal with the name <replaceable>member</replaceable>,
          parameter signature <replaceable>signature</replaceable>, and argument names
          <replaceable>names</replaceable>. <replaceable>names</replaceable> should be
          created using the <constant>SD_BUS_PARAM()</constant> macro, see below.
          Parameter <replaceable>flags</replaceable> is a combination of flags, see below.
          </para>

          <para>Equivalent to <constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> with the
          <replaceable>names</replaceable> parameter unset (i.e. no parameter names).</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_WRITABLE_PROPERTY()</constant></term>
          <term><constant>SD_BUS_PROPERTY()</constant></term>

          <listitem><para>Declare a D-Bus property with the name <replaceable>member</replaceable> and value
          signature <replaceable>signature</replaceable>. Parameters <replaceable>get</replaceable> and
          <replaceable>set</replaceable> are the getter and setter methods. They are called with a pointer
          that is the <replaceable>userdata</replaceable> parameter passed to the registration function
          offset by <replaceable>offset</replaceable> bytes. This may be used pass pointers to different
          fields in the same data structure to different setters and getters in the same vtable. Parameter
          <replaceable>flags</replaceable> is a combination of flags, see below.</para>

          <para>The setter and getter methods may be omitted (specified as <constant>NULL</constant>), if the
          property has one of the basic types or <literal>as</literal> in case of read-only properties. In
          those cases, the <replaceable>userdata</replaceable> and <replaceable>offset</replaceable>
          parameters must together point to valid variable of the corresponding type. A default setter and
          getters will be provided, which simply copy the argument between this variable and the message.
          </para>

          <para><constant>SD_BUS_PROPERTY()</constant> is used to define a read-only property.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_PARAM()</constant></term>
          <listitem><para>Parameter names should be wrapped in this macro, see the example below.</para>
          </listitem>
        </varlistentry>
      </variablelist>
    </refsect2>

    <refsect2>
      <title>Flags</title>

      <para>The <replaceable>flags</replaceable> parameter is used to specify a combination of
      <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format">D-Bus annotations</ulink>.
      </para>

      <variablelist>
        <varlistentry>
          <term><constant>SD_BUS_VTABLE_DEPRECATED</constant></term>

          <listitem><para>Mark this vtable entry as deprecated using the
          <constant>org.freedesktop.DBus.Deprecated</constant> annotation in introspection data.  If
          specified for <constant>SD_BUS_VTABLE_START()</constant>, the annotation is applied to the
          enclosing interface.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_VTABLE_HIDDEN</constant></term>

          <listitem><para>Make this vtable entry hidden. It will not be shown in introspection data.  If
          specified for <constant>SD_BUS_VTABLE_START()</constant>, all entries in the array are hidden.
          </para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_VTABLE_UNPRIVILEGED</constant></term>

          <listitem><para>Mark this vtable entry as unprivileged. If not specified, the
          <constant>org.freedesktop.systemd1.Privileged</constant> annotation with value
          <literal>true</literal> will be shown in introspection data.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_VTABLE_METHOD_NO_REPLY</constant></term>

          <listitem><para>Mark his vtable entry as a method that will not return a reply using the
          <constant>org.freedesktop.DBus.Method.NoReply</constant> annotation in introspection data.
          </para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_VTABLE_PROPERTY_CONST</constant></term>
          <term><constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant></term>
          <term><constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant></term>

          <listitem><para>Those three flags correspond to different values of the
          <constant>org.freedesktop.DBus.Property.EmitsChangedSignal</constant> annotation, which specifies
          whether the <constant>org.freedesktop.DBus.Properties.PropertiesChanged</constant> signal is
          emitted whenever the property changes. <constant>SD_BUS_VTABLE_PROPERTY_CONST</constant> corresponds to
          <constant>const</constant> and means that the property never changes during the lifetime of the
          object it belongs to, so no signal needs to be emitted.
          <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant> corresponds to <constant>true</constant> and means
          that the signal is emitted. <constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant> corresponds to
          <constant>invalidates</constant> and means that the signal is emitted, but the value is not included
          in the signal.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>SD_BUS_VTABLE_PROPERTY_EXPLICIT</constant></term>

          <listitem><para>Mark this vtable property entry as requiring explicit request to for the value to
          be shown (generally because the value is large or slow to calculate). This entry cannot be combined
          with <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant>, and will not be shown in property listings by
          default (e.g. <command>busctl introspect</command>).  This corresponds to the
          <constant>org.freedesktop.systemd1.Explicit</constant> annotation in introspection data.</para>
          </listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Create a simple listener on the bus</title>

      <programlisting><xi:include href="vtable-example.c" parse="text" /></programlisting>

      <para>This creates a simple client on the bus (the user bus, when run as normal user).
      We may use the D-Bus <constant>org.freedesktop.DBus.Introspectable.Introspect</constant>
      call to acquire the XML description of the interface:</para>

      <programlisting><xi:include href="vtable-example.xml" parse="text" /></programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, <function>sd_bus_add_object_vtable</function> and
    <function>sd_bus_add_fallback_vtable</function> calls return 0 or a positive integer. On failure, they
    return a negative errno-style error code.</para>

    <refsect2>
      <title>Errors</title>

      <para>Returned errors may indicate the following problems:</para>

      <variablelist>
        <varlistentry>
          <term><constant>-EINVAL</constant></term>

          <listitem><para>One of the required parameters is <constant>NULL</constant> or invalid. A reserved
          D-Bus interface was passed as the <replaceable>interface</replaceable> parameter.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOPKG</constant></term>

          <listitem><para>The bus cannot be resolved.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ECHILD</constant></term>

          <listitem><para>The bus was created in a different process.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOMEM</constant></term>

          <listitem><para>Memory allocation failed.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EPROTOTYPE</constant></term>

          <listitem><para><function>sd_bus_add_object_vtable</function> and
          <function>sd_bus_add_fallback_vtable</function> have been both called
          for the same bus object path, which is not allowed.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EEXIST</constant></term>

          <listitem><para>This vtable has already been registered for this
          <replaceable>interface</replaceable> and <replaceable>path</replaceable>.
          </para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>busctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>