man/sd_bus_negotiate_fds.xml

<?xml version='1.0'?>
<!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_negotiate_fds" xmlns:xi="http://www.w3.org/2001/XInclude">

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

      <funcprototype>
        <funcdef>int <function>sd_bus_get_creds_mask</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</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><function>sd_bus_get_creds_mask()</function> returns the set of sender credentials that was
    negotiated to be attached to all incoming messages in <parameter>mask</parameter>. This value is an
    upper boundary only. Hence, always make sure to explicitly check which credentials are attached to a
    specific message before using it.</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 a non-negative integer. On failure, they return a negative
    errno-style error code.</para>

    <refsect2>
      <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>

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

          <listitem><para>An argument is invalid.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOPKG</constant></term>

          <listitem><para>The bus cannot be resolved.</para></listitem>
        </varlistentry>

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

          <listitem><para>The bus was created in a different process.</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_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_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>