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<refentry id="sd_bus_negotiate_fds">

  <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_timestamp</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>
        <paramdef>uint64_t <parameter>mask</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. In particular, networked transports generally
    do not 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><function>sd_bus_negotiate_timestamp()</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.  Use
    <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_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    to query the timestamps of incoming messages. If negotiation is disabled or not supported, these
    calls will fail with <constant>-ENODATA</constant>. Note that currently no transports support
    timestamping of messages. By default, message timestamping is not negotiated for
    connections.</para>

    <para><function>sd_bus_negotiate_creds()</function> controls whether and which implicit sender
    credentials shall be attached automatically to all incoming messages. Takes a bus object and a
    boolean indicating whether to enable or disable the credential parts encoded in the bit mask
    value argument. Note that not all transports support attaching sender credentials to messages,
    or do not support all types of sender credential parameters, or might suppress them under
    certain circumstances for individual messages. Specifically, dbus1 only supports
    <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender credentials are suitable for
    authorization decisions. By default, only <constant>SD_BUS_CREDS_WELL_KNOWN_NAMES</constant> and
    <constant>SD_BUS_CREDS_UNIQUE_NAME</constant> are enabled. In fact, these two credential fields
    are always sent along and cannot be turned off.</para>

    <para>The <function>sd_bus_negotiate_fds()</function> function may
    be called only before the connection has been started with
    <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
    <function>sd_bus_negotiate_timestamp()</function> and
    <function>sd_bus_negotiate_creds()</function> may also be called
    after a connection has been set up. Note that, when operating on a
    connection that is shared between multiple components of the same
    program (for example via
    <citerefentry><refentrytitle>sd_bus_default</refentrytitle><manvolnum>3</manvolnum></citerefentry>),
    it is highly recommended to only enable additional per message
    metadata fields, but never disable them again, in order not to
    disable functionality needed by other components.</para>
  </refsect1>

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

    <para>On success, these functions return 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_fds()</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_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
