man/sd_bus_emit_signal.xml

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<!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_emit_signal"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_bus_emit_signal</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_emit_signal</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_emit_signal</refname>
    <refname>sd_bus_emit_signalv</refname>
    <refname>sd_bus_emit_interfaces_added</refname>
    <refname>sd_bus_emit_interfaces_added_strv</refname>
    <refname>sd_bus_emit_interfaces_removed</refname>
    <refname>sd_bus_emit_interfaces_removed_strv</refname>
    <refname>sd_bus_emit_properties_changed</refname>
    <refname>sd_bus_emit_properties_changed_strv</refname>
    <refname>sd_bus_emit_object_added</refname>
    <refname>sd_bus_emit_object_removed</refname>

    <refpurpose>Convenience functions for emitting (standard) D-Bus signals</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_signal</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>member</parameter></paramdef>
        <paramdef>const char *<parameter>types</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_signalv</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>member</parameter></paramdef>
        <paramdef>const char *<parameter>types</parameter></paramdef>
        <paramdef>va_list <parameter>ap</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_interfaces_added</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_interfaces_added_strv</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char **<parameter>interfaces</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_interfaces_removed</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_interfaces_removed_strv</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char **<parameter>interfaces</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_properties_changed</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>name</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_properties_changed_strv</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>names</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_object_added</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_emit_object_removed</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_emit_signal()</function> is a convenience function for initializing a
    bus message object and emitting the corresponding D-Bus signal. It combines the
    <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
    <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    functions into a single function call. <function>sd_bus_emit_signalv()</function> is
    equivalent to <function>sd_bus_message_append()</function>, except that it is called with a
    <literal>va_list</literal> instead of a variable number of arguments.</para>

    <para><function>sd_bus_emit_interfaces_added()</function> and
    <function>sd_bus_emit_interfaces_removed()</function> are used to implement the
    <function>InterfacesAdded</function> and <function>InterfacesRemoved</function> signals of the
    <constant>org.freedesktop.DBus.ObjectManager</constant> interface. They take a path whose
    interfaces have been modified as an argument and a variable list of interfaces that have been
    added or removed, respectively. The final argument passed to
    <function>sd_bus_emit_interfaces_added()</function> and
    <function>sd_bus_emit_interfaces_removed()</function> <emphasis>must</emphasis> be
    <constant>NULL</constant>. This allows both functions to safely determine the number of passed
    interface arguments. <function>sd_bus_emit_interfaces_added_strv()</function> and
    <function>sd_bus_emit_interfaces_removed_strv()</function> are identical to their respective
    counterparts but both take the list of interfaces as a single argument instead of a variable
    number of arguments.</para>

    <para><function>sd_bus_emit_properties_changed()</function> is used to implement the
    <function>PropertiesChanged</function> signal of the
    <constant>org.freedesktop.DBus.Properties</constant> interface. It takes an object path,
    interface and a variable list of property names as its arguments.  The final argument passed to
    <function>sd_bus_emit_properties_changed()</function> <emphasis>must</emphasis> be
    <constant>NULL</constant>. This allows it to safely determine the number of passed property
    names. <function>sd_bus_emit_properties_changed_strv()</function> is identical to
    <function>sd_bus_emit_properties_changed()</function> but takes the list of property names as a
    single argument instead of a variable number of arguments.</para>

    <para><function>sd_bus_emit_object_added()</function> and
    <function>sd_bus_emit_object_removed()</function> are convenience functions for emitting the
    <function>InterfacesAdded</function> or <function>InterfacesRemoved</function> signals for all
    interfaces registered on a specific object path, respectively. This includes any parent fallback
    vtables if they are not overridden by a more applicable child vtable. It also includes all the
    standard D-Bus interfaces implemented by sd-bus itself on any registered object.</para>

    <para>Note that <function>sd_bus_emit_interfaces_added()</function>,
    <function>sd_bus_emit_interfaces_removed()</function>,
    <function>sd_bus_emit_object_added()</function> and
    <function>sd_bus_emit_object_removed()</function> require an object manager to have been
    registered on the given object path or one of its parent object paths using
    <citerefentry><refentrytitle>sd_bus_add_object_manager</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>
  </refsect1>

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

    <para>On success, these functions return a non-negative 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>-ESRCH</constant></term>

          <listitem><para>One of <function>sd_bus_emit_interfaces_added()</function>,
          <function>sd_bus_emit_interfaces_removed()</function>,
          <function>sd_bus_emit_object_added()</function> or
          <function>sd_bus_emit_object_removed()</function> was called on an object without an
          object manager registered on its own object path or one of its parent object paths.
          </para></listitem>
        </varlistentry>
      </variablelist>

      <para>See the man pages of
      <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
      <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
      for more possible errors.</para>
    </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>,
      <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>