systemd/man/sd_bus_send.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-or-later -->

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

  <refentryinfo>
    <title>sd_bus_send</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_send</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_send</refname>
    <refname>sd_bus_send_to</refname>
    <refname>sd_bus_message_send</refname>

    <refpurpose>Queue a D-Bus message for transfer</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_send</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_send_to</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>const char *<parameter>destination</parameter></paramdef>
        <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int sd_bus_message_send</funcdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_send()</function> queues the bus message object <parameter>m</parameter> for
    transfer. If <parameter>bus</parameter> is <constant>NULL</constant>, the bus that
    <parameter>m</parameter> is attached to is used. <parameter>bus</parameter> only needs to be set when the
    message is sent to a different bus than the one it's attached to, for example when forwarding messages.
    If the output parameter <parameter>cookie</parameter> is not <constant>NULL</constant>, it is set to the
    message identifier. This value can later be used to match incoming replies to their corresponding
    messages. If <parameter>cookie</parameter> is set to <constant>NULL</constant> and the message is not
    sealed, <function>sd_bus_send()</function> assumes the message <parameter>m</parameter> doesn't expect a
    reply and adds the necessary headers to indicate this.</para>

    <para>Note that in most scenarios, <function>sd_bus_send()</function> should not be called
    directly. Instead, use higher level functions such as
    <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
    <citerefentry><refentrytitle>sd_bus_reply_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    which call <function>sd_bus_send()</function> internally.</para>

    <para><function>sd_bus_send_to()</function> is a shorthand for sending a message to a specific
    destination. It's main use case is to simplify sending unicast signal messages (signals that only have a
    single receiver). It's behavior is similar to calling
    <citerefentry><refentrytitle>sd_bus_message_set_destination</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    followed by calling <function>sd_bus_send()</function>.</para>

    <para><function>sd_bus_send()</function>/<function>sd_bus_send_to()</function> will write the message
    directly to the underlying transport (e.g. kernel socket buffer) if possible. If the connection is not
    set up fully yet the message is queued locally. If the transport buffers are congested any unwritten
    message data is queued locally, too. If the connection has been closed or is currently being closed the
    call fails.
    <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry> should
    be invoked to write out any queued message data to the transport.</para>

    <para><function>sd_bus_message_send()</function> is the same as <function>sd_bus_send()</function> but
    without the first and last argument. <function>sd_bus_message_send(m)</function> is equivalent to
    <function>sd_bus_send(sd_bus_message_get_bus(m), m, NULL)</function>.</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>
        </varlistentry>

        <varlistentry>
          <term><constant>-EOPNOTSUPP</constant></term>

          <listitem><para>The bus connection does not support sending file descriptors.
          </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>-ENOBUFS</constant></term>

          <listitem><para>The bus connection's write queue is full.</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>-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_message_set_destination</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_reply_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>