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<refentry id="sd_bus_negotiate_fds" conditional="ENABLE_KDBUS">

  <refentryinfo>
    <title>sd_bus_negotiate_fds</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_negotiate_fds</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_negotiate_fds</refname>
    <refname>sd_bus_negotiate_timestamps</refname>
    <refname>sd_bus_negotiate_creds</refname>

    <refpurpose>Control feature negotiation on bus connections</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_negotiate_fds</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>int <parameter>b</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_negotiate_timestamp</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>int <parameter>b</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>int <parameter>b</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_negotiate_fds()</function> controls whether
    file descriptor passing shall be negotiated for the specified bus
    connection. It takes a bus object and a boolean, which, when true,
    enables file descriptor passing, and, when false, disables it. Note
    that not all transports and servers support file descriptor
    passing. To find out whether file descriptor passing is available
    after negotiation, use
    <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file
    descriptor passing is always enabled for both sending and
    receiving or for neither, but never only in one direction. By
    default, file descriptor passing is negotiated for all
    connections.</para>

    <para>Note that when bus activation is used, it is highly
    recommended to set the <option>AcceptFileDescriptors=</option>
    setting in the <filename>.busname</filename> unit file to the same
    setting as negotiated by the program ultimately activated. By
    default, file descriptor passing is enabled for both.</para>

    <para><function>sd_bus_negotiate_timestamps()</function> controls
    whether implicit sender timestamps shall be attached automatically
    to all incoming messages. Takes a bus object and a boolean, which,
    when true, enables timestamping, and, when false, disables it. If
    this is disabled,
    <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_message_get_seqno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    fail with <constant>-ENODATA</constant> on incoming messages. Note
    that not all transports support timestamping of messages. On local
    transports, the timestamping is applied by the kernel and cannot be
    manipulated by userspace.</para>

    <para><function>sd_bus_negotiate_creds()</function> controls
    whether implicit sender credentials shall be attached
    automatically to all incoming messages. Takes a bus object and a
    bit mask value, which controls which credential parameters are
    attached. If this is not used,
    <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    fails with <constant>-ENODATA</constant> on incoming
    messages. Note that not all transports support attaching sender
    credentials to messages, or do not support all types of sender
    credential parameters. On local transports, the sender credentials
    are attached by the kernel and cannot be manipulated by
    userspace. By default, no sender credentials are attached.</para>

    <para>These functions may be called only before the connection has
    been started with
    <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  </refsect1>

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

    <para>On success, these functions returns 0 or a
    positive integer. On failure, they return a negative errno-style
    error code.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

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

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

        <listitem><para>The bus connection has already been started.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para><function>sd_bus_negotiate_fs()</function> and the other
    functions described here are available as a shared library, which
    can be compiled and linked to with the
    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    file.</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>,
      <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
