man/sd_bus_negotiate_fds.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_bus_negotiate_fds" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_bus_negotiate_fds</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_bus_negotiate_fds</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_bus_negotiate_fds</refname>
  23     <refname>sd_bus_negotiate_timestamp</refname>
  24     <refname>sd_bus_negotiate_creds</refname>
  25
  26     <refpurpose>Control feature negotiation on bus connections</refpurpose>
  27   </refnamediv>
  28
  29   <refsynopsisdiv>
  30     <funcsynopsis>
  31       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  32
  33       <funcprototype>
  34         <funcdef>int <function>sd_bus_negotiate_fds</function></funcdef>
  35         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  36         <paramdef>int <parameter>b</parameter></paramdef>
  37       </funcprototype>
  38
  39       <funcprototype>
  40         <funcdef>int <function>sd_bus_negotiate_timestamp</function></funcdef>
  41         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  42         <paramdef>int <parameter>b</parameter></paramdef>
  43       </funcprototype>
  44
  45       <funcprototype>
  46         <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
  47         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  48         <paramdef>int <parameter>b</parameter></paramdef>
  49         <paramdef>uint64_t <parameter>mask</parameter></paramdef>
  50       </funcprototype>
  51     </funcsynopsis>
  52   </refsynopsisdiv>
  53
  54   <refsect1>
  55     <title>Description</title>
  56
  57     <para><function>sd_bus_negotiate_fds()</function> controls whether
  58     file descriptor passing shall be negotiated for the specified bus
  59     connection. It takes a bus object and a boolean, which, when true,
  60     enables file descriptor passing, and, when false, disables
  61     it. Note that not all transports and servers support file
  62     descriptor passing. In particular, networked transports generally
  63     do not support file descriptor passing. To find out whether file
  64     descriptor passing is available after negotiation, use
  65     <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  66     and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file
  67     descriptor passing is always enabled for both sending and
  68     receiving or for neither, but never only in one direction. By
  69     default, file descriptor passing is negotiated for all
  70     connections.</para>
  71
  72     <para><function>sd_bus_negotiate_timestamp()</function> controls whether implicit sender
  73     timestamps shall be attached automatically to all incoming messages. Takes a bus object and a
  74     boolean, which, when true, enables timestamping, and, when false, disables it.  Use
  75     <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  76     <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  77     <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  78     to query the timestamps of incoming messages. If negotiation is disabled or not supported, these
  79     calls will fail with <constant>-ENODATA</constant>. Note that currently no transports support
  80     timestamping of messages. By default, message timestamping is not negotiated for
  81     connections.</para>
  82
  83     <para><function>sd_bus_negotiate_creds()</function> controls whether and which implicit sender
  84     credentials shall be attached automatically to all incoming messages. Takes a bus object and a
  85     boolean indicating whether to enable or disable the credential parts encoded in the bit mask
  86     value argument. Note that not all transports support attaching sender credentials to messages,
  87     or do not support all types of sender credential parameters, or might suppress them under
  88     certain circumstances for individual messages. Specifically, dbus1 only supports
  89     <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender credentials are suitable for
  90     authorization decisions. By default, only <constant>SD_BUS_CREDS_WELL_KNOWN_NAMES</constant> and
  91     <constant>SD_BUS_CREDS_UNIQUE_NAME</constant> are enabled. In fact, these two credential fields
  92     are always sent along and cannot be turned off.</para>
  93
  94     <para>The <function>sd_bus_negotiate_fds()</function> function may
  95     be called only before the connection has been started with
  96     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
  97     <function>sd_bus_negotiate_timestamp()</function> and
  98     <function>sd_bus_negotiate_creds()</function> may also be called
  99     after a connection has been set up. Note that, when operating on a
 100     connection that is shared between multiple components of the same
 101     program (for example via
 102     <citerefentry><refentrytitle>sd_bus_default</refentrytitle><manvolnum>3</manvolnum></citerefentry>),
 103     it is highly recommended to only enable additional per message
 104     metadata fields, but never disable them again, in order not to
 105     disable functionality needed by other components.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>Return Value</title>
 110
 111     <para>On success, these functions return 0 or a
 112     positive integer. On failure, they return a negative errno-style
 113     error code.</para>
 114   </refsect1>
 115
 116   <refsect1>
 117     <title>Errors</title>
 118
 119     <para>Returned errors may indicate the following problems:</para>
 120
 121     <variablelist>
 122       <varlistentry>
 123         <term><constant>-EPERM</constant></term>
 124
 125         <listitem><para>The bus connection has already been started.</para></listitem>
 126       </varlistentry>
 127     </variablelist>
 128   </refsect1>
 129
 130   <xi:include href="libsystemd-pkgconfig.xml" />
 131
 132   <refsect1>
 133     <title>See Also</title>
 134
 135     <para>
 136       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 137       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 139       <citerefentry><refentrytitle>sd_bus_message_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 140       <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 141       <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 142       <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 143       <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 144     </para>
 145   </refsect1>
 146
 147 </refentry>