systemd/man/sd_bus_add_match.xml

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<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> installs a match rule for incoming messages received on the specified bus
      connection object <parameter>bus</parameter>. The syntax of the match rule expression passed in
      <parameter>match</parameter> is described in the <ulink
      url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>. The specified handler
      function <parameter>callback</parameter> is called for eaching incoming message matching the specified
      expression, the <parameter>userdata</parameter> parameter is passed as-is to the callback function.
    </para>

    <para>
      On success, and if non-<constant>NULL</constant>, the <parameter>slot</parameter> return parameter will be set to
      a slot object that may be used as a reference to the installed match, and may be utilized to remove it again at a
      later time with
      <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
      specified as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the match
      cannot be removed independently.
    </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>