man/sd_bus_negotiate_fds.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_bus_negotiate_fds" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_bus_negotiate_fds</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_bus_negotiate_fds</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_bus_negotiate_fds</refname>
  20     <refname>sd_bus_negotiate_timestamp</refname>
  21     <refname>sd_bus_negotiate_creds</refname>
  22
  23     <refpurpose>Control feature negotiation on bus connections</refpurpose>
  24   </refnamediv>
  25
  26   <refsynopsisdiv>
  27     <funcsynopsis>
  28       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  29
  30       <funcprototype>
  31         <funcdef>int <function>sd_bus_negotiate_fds</function></funcdef>
  32         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  33         <paramdef>int <parameter>b</parameter></paramdef>
  34       </funcprototype>
  35
  36       <funcprototype>
  37         <funcdef>int <function>sd_bus_negotiate_timestamp</function></funcdef>
  38         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  39         <paramdef>int <parameter>b</parameter></paramdef>
  40       </funcprototype>
  41
  42       <funcprototype>
  43         <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
  44         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  45         <paramdef>int <parameter>b</parameter></paramdef>
  46         <paramdef>uint64_t <parameter>mask</parameter></paramdef>
  47       </funcprototype>
  48     </funcsynopsis>
  49   </refsynopsisdiv>
  50
  51   <refsect1>
  52     <title>Description</title>
  53
  54     <para><function>sd_bus_negotiate_fds()</function> controls whether
  55     file descriptor passing shall be negotiated for the specified bus
  56     connection. It takes a bus object and a boolean, which, when true,
  57     enables file descriptor passing, and, when false, disables
  58     it. Note that not all transports and servers support file
  59     descriptor passing. In particular, networked transports generally
  60     do not support file descriptor passing. To find out whether file
  61     descriptor passing is available after negotiation, use
  62     <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  63     and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file
  64     descriptor passing is always enabled for both sending and
  65     receiving or for neither, but never only in one direction. By
  66     default, file descriptor passing is negotiated for all
  67     connections.</para>
  68
  69     <para><function>sd_bus_negotiate_timestamp()</function> controls whether implicit sender
  70     timestamps shall be attached automatically to all incoming messages. Takes a bus object and a
  71     boolean, which, when true, enables timestamping, and, when false, disables it.  Use
  72     <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  73     <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  74     <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  75     to query the timestamps of incoming messages. If negotiation is disabled or not supported, these
  76     calls will fail with <constant>-ENODATA</constant>. Note that currently no transports support
  77     timestamping of messages. By default, message timestamping is not negotiated for
  78     connections.</para>
  79
  80     <para><function>sd_bus_negotiate_creds()</function> controls whether and which implicit sender
  81     credentials shall be attached automatically to all incoming messages. Takes a bus object and a
  82     boolean indicating whether to enable or disable the credential parts encoded in the bit mask
  83     value argument. Note that not all transports support attaching sender credentials to messages,
  84     or do not support all types of sender credential parameters, or might suppress them under
  85     certain circumstances for individual messages. Specifically, dbus1 only supports
  86     <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender credentials are suitable for
  87     authorization decisions. By default, only <constant>SD_BUS_CREDS_WELL_KNOWN_NAMES</constant> and
  88     <constant>SD_BUS_CREDS_UNIQUE_NAME</constant> are enabled. In fact, these two credential fields
  89     are always sent along and cannot be turned off.</para>
  90
  91     <para>The <function>sd_bus_negotiate_fds()</function> function may
  92     be called only before the connection has been started with
  93     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
  94     <function>sd_bus_negotiate_timestamp()</function> and
  95     <function>sd_bus_negotiate_creds()</function> may also be called
  96     after a connection has been set up. Note that, when operating on a
  97     connection that is shared between multiple components of the same
  98     program (for example via
  99     <citerefentry><refentrytitle>sd_bus_default</refentrytitle><manvolnum>3</manvolnum></citerefentry>),
 100     it is highly recommended to only enable additional per message
 101     metadata fields, but never disable them again, in order not to
 102     disable functionality needed by other components.</para>
 103   </refsect1>
 104
 105   <refsect1>
 106     <title>Return Value</title>
 107
 108     <para>On success, these functions return 0 or a
 109     positive integer. On failure, they return a negative errno-style
 110     error code.</para>
 111
 112     <refsect2>
 113       <title>Errors</title>
 114
 115       <para>Returned errors may indicate the following problems:</para>
 116
 117       <variablelist>
 118         <varlistentry>
 119           <term><constant>-EPERM</constant></term>
 120
 121           <listitem><para>The bus connection has already been started.</para></listitem>
 122         </varlistentry>
 123       </variablelist>
 124     </refsect2>
 125   </refsect1>
 126
 127   <xi:include href="libsystemd-pkgconfig.xml" />
 128
 129   <refsect1>
 130     <title>See Also</title>
 131
 132     <para>
 133       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 134       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 135       <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 136       <citerefentry><refentrytitle>sd_bus_message_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137       <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 139       <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 140       <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 141     </para>
 142   </refsect1>
 143
 144 </refentry>