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>

      <xi:include href="sd_bus_add_match.xml" xpointer="sd_bus_message_handler_t"/>

      <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 finishes, 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. (Note that the
    <structname>sd_bus_error</structname> parameter is an output parameter of the callback function, not an
    input parameter; it can be used to propagate errors from the callback handler, it will not receive any
    error that was received as method reply.)</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 <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>When <function>sd_bus_call()</function> internally receives a D-Bus error reply, it will set
      <parameter>ret_error</parameter> if it is not <constant>NULL</constant>, and will return a negative
      value mapped from the error reply, see
      <citerefentry><refentrytitle>sd_bus_error_get_errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
      </para>

      <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>,
      <citerefentry><refentrytitle>sd_bus_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>