core: use the correct APIs to determine whether a dual timestamp is initialized

[thirdparty/systemd.git] / man / sd_bus_add_match.xml

<?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.

  Copyright 2016 Julian Orth

  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.

  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_add_match">

  <refentryinfo>
    <title>sd_bus_add_match</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <firstname>Julian</firstname>
        <surname>Orth</surname>
        <email>ju.orth@gmail.com</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_add_match</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_add_match</refname>

    <refpurpose>Add a match rule for message dispatching</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_add_match</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
        <paramdef>const char *<parameter>match</parameter></paramdef>
        <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <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>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>
      <function>sd_bus_add_match()</function> adds a match rule used to dispatch
      incoming messages. The syntax of the rule passed in
      <parameter>match</parameter> is described in the
      <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>.
    </para>

    <para>
      The message <parameter>m</parameter> passed to the callback is only
      borrowed, that is, the callback should not call
      <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
      on it. If the callback wants to hold on to the message beyond the lifetime
      of the callback, it needs to call
      <citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
      to create a new reference.
    </para>

    <para>
      If an error occurs during the callback invocation, the callback should
      return a negative error number. If it wants other callbacks that match the
      same rule to be called, it should return 0. Otherwise it should return a
      positive integer.
    </para>
  </refsect1>

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

    <para>
      On success, <function>sd_bus_add_match()</function> returns 0 or a
      positive integer. On failure, it returns a negative errno-style error
      code.
    </para>
  </refsect1>

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

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

</refentry>