systemd/man/sd_bus_call.xml

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

  <refentryinfo>
    <title>sd_bus_call</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_call</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_call</refname>
    <refname>sd_bus_call_async</refname>

    <refpurpose>Invoke a D-Bus method call</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_call</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
        <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
        <paramdef>sd_bus_message **<parameter>reply</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_call_async</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_call()</function> takes a complete bus message object and calls the
    corresponding D-Bus method. On success, the response is stored in <parameter>reply</parameter>.
    <parameter>usec</parameter> indicates the timeout in microseconds. If
    <parameter>ret_error</parameter> is not <constant>NULL</constant> and
    <function>sd_bus_call()</function> fails (either because of an internal error or because it
    received a D-Bus error reply), <parameter>ret_error</parameter> is initialized to an instance of
    <structname>sd_bus_error</structname> describing the error.</para>

    <para><function>sd_bus_call_async()</function> is like <function>sd_bus_call()</function> but
    works asynchronously. The <parameter>callback</parameter> indicates the function to call when
    the response arrives. The <parameter>userdata</parameter> pointer will be passed to the callback
    function, and may be chosen freely by the caller. If <parameter>slot</parameter> is not
    <constant>NULL</constant> and <function>sd_bus_call_async()</function> succeeds,
    <parameter>slot</parameter> is set to a slot object which can be used to cancel the method call
    at a later time using
    <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    If <parameter>slot</parameter> is <constant>NULL</constant>, the lifetime of the method call is
    bound to the lifetime of the bus object itself, and it cannot be cancelled independently. See
    <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for details. <parameter>callback</parameter> is called when a reply arrives with the reply,
    <parameter>userdata</parameter> and an <structname>sd_bus_error</structname> output
    parameter as its arguments. Unlike <function>sd_bus_call()</function>, the
    <structname>sd_bus_error</structname> output parameter passed to the callback will be empty. To
    determine whether the method call succeeded, use
    <citerefentry><refentrytitle>sd_bus_message_is_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    on the reply message passed to the callback instead. If the callback returns zero and the
    <structname>sd_bus_error</structname> output parameter is still empty when the callback
    inishes, other handlers registered with functions such as
    <citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    are given a chance to process the message. If the callback returns a non-zero value or the
    <structname>sd_bus_error</structname> output parameter is not empty when the callback finishes,
    no further processing of the message is done. Generally, you want to return zero from the
    callback to give other registered handlers a chance to process the reply as well.</para>

    <para>If <parameter>usec</parameter> is zero, the default D-Bus method call timeout is used. See
    <citerefentry><refentrytitle>sd_bus_get_method_call_timeout</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 id='errors'>
      <title>Errors</title>

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

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

          <listitem><para>The input parameter <parameter>m</parameter> is <constant>NULL</constant>.
          </para></listitem>

          <listitem><para>The input parameter <parameter>m</parameter> is not a D-Bus method call.
          To create a new D-Bus method call, use
          <citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
          </para></listitem>

          <listitem><para>The input parameter <parameter>m</parameter> has the
          <constant>BUS_MESSAGE_NO_REPLY_EXPECTED</constant> flag set.</para></listitem>

          <listitem><para>The input parameter <parameter>error</parameter> is
          non-<constant>NULL</constant> but was not set to <constant>SD_BUS_ERROR_NULL</constant>.
          </para></listitem>
        </varlistentry>

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

          <listitem><para>The bus connection was allocated in a parent process and is being reused
          in a child process after <function>fork()</function>.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOTCONN</constant></term>

          <listitem><para>The input parameter <parameter>bus</parameter> is
          <constant>NULL</constant> or the bus is not connected.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ECONNRESET</constant></term>

          <listitem><para>The bus connection was closed while waiting for the response.
          </para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ETIMEDOUT</constant></term>

          <listitem><para>A response was not received within the given timeout.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ELOOP</constant></term>

          <listitem><para>The message <parameter>m</parameter> is addressed to its own client.
          </para></listitem>
        </varlistentry>

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

          <listitem><para>Memory allocation failed.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

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

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

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_call_method_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>