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     <refname>sd_bus_get_creds_mask</refname>
  23
  24     <refpurpose>Control feature negotiation on bus connections</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <funcsynopsis>
  29       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  30
  31       <funcprototype>
  32         <funcdef>int <function>sd_bus_negotiate_fds</function></funcdef>
  33         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  34         <paramdef>int <parameter>b</parameter></paramdef>
  35       </funcprototype>
  36
  37       <funcprototype>
  38         <funcdef>int <function>sd_bus_negotiate_timestamp</function></funcdef>
  39         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  40         <paramdef>int <parameter>b</parameter></paramdef>
  41       </funcprototype>
  42
  43       <funcprototype>
  44         <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
  45         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  46         <paramdef>int <parameter>b</parameter></paramdef>
  47         <paramdef>uint64_t <parameter>mask</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>int <function>sd_bus_get_creds_mask</function></funcdef>
  52         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  53         <paramdef>uint64_t *<parameter>mask</parameter></paramdef>
  54       </funcprototype>
  55     </funcsynopsis>
  56   </refsynopsisdiv>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <para><function>sd_bus_negotiate_fds()</function> controls whether file descriptor passing shall be
  62     negotiated for the specified bus connection. It takes a bus object and a boolean, which, when true,
  63     enables file descriptor passing, and, when false, disables it. Note that not all transports and servers
  64     support file descriptor passing. In particular, networked transports generally do not support file
  65     descriptor passing. To find out whether file descriptor passing is available after negotiation, use
  66     <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  67     and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file descriptor passing is always enabled
  68     for both sending and receiving or for neither, but never only in one direction. By default, file
  69     descriptor passing is negotiated for all connections.</para>
  70
  71     <para><function>sd_bus_negotiate_timestamp()</function> controls whether implicit sender timestamps shall
  72     be attached automatically to all incoming messages. Takes a bus object and a boolean, which, when true,
  73     enables timestamping, and, when false, disables it.  Use
  74     <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  75     <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  76     <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  77     to query the timestamps of incoming messages. If negotiation is disabled or not supported, these calls
  78     will fail with <constant>-ENODATA</constant>. Note that currently no transports support timestamping of
  79     messages. By default, message timestamping is not negotiated for connections.</para>
  80
  81     <para><function>sd_bus_negotiate_creds()</function> controls whether and which implicit sender
  82     credentials shall be attached automatically to all incoming messages. Takes a bus object and a boolean
  83     indicating whether to enable or disable the credential parts encoded in the bit mask value argument. Note
  84     that not all transports support attaching sender credentials to messages, or do not support all types of
  85     sender credential parameters, or might suppress them under certain circumstances for individual messages.
  86     Specifically, dbus1 only supports <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender credentials
  87     are suitable for authorization decisions. By default, only
  88     <constant>SD_BUS_CREDS_WELL_KNOWN_NAMES</constant> and <constant>SD_BUS_CREDS_UNIQUE_NAME</constant> are
  89     enabled. In fact, these two credential fields are always sent along and cannot be turned off.</para>
  90
  91     <para><function>sd_bus_get_creds_mask()</function> returns the set of sender credentials that was
  92     negotiated to be attached to all incoming messages in <parameter>mask</parameter>. This value is an
  93     upper boundary only. Hence, always make sure to explicitly check which credentials are attached to a
  94     specific message before using it.</para>
  95
  96     <para>The <function>sd_bus_negotiate_fds()</function> function may be called only before the connection
  97     has been started with
  98     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
  99     <function>sd_bus_negotiate_timestamp()</function> and <function>sd_bus_negotiate_creds()</function> may
 100     also be called after a connection has been set up. Note that, when operating on a connection that is
 101     shared between multiple components of the same program (for example via
 102     <citerefentry><refentrytitle>sd_bus_default</refentrytitle><manvolnum>3</manvolnum></citerefentry>), it
 103     is highly recommended to only enable additional per message metadata fields, but never disable them
 104     again, in order not to disable functionality needed by other components.</para>
 105   </refsect1>
 106
 107   <refsect1>
 108     <title>Return Value</title>
 109
 110     <para>On success, these functions return a non-negative integer. On failure, they return a negative
 111     errno-style error code.</para>
 112
 113     <refsect2>
 114       <title>Errors</title>
 115
 116       <para>Returned errors may indicate the following problems:</para>
 117
 118       <variablelist>
 119         <varlistentry>
 120           <term><constant>-EPERM</constant></term>
 121
 122           <listitem><para>The bus connection has already been started.</para></listitem>
 123         </varlistentry>
 124
 125         <varlistentry>
 126           <term><constant>-EINVAL</constant></term>
 127
 128           <listitem><para>An argument is invalid.</para></listitem>
 129         </varlistentry>
 130
 131         <varlistentry>
 132           <term><constant>-ENOPKG</constant></term>
 133
 134           <listitem><para>The bus cannot be resolved.</para></listitem>
 135         </varlistentry>
 136
 137         <varlistentry>
 138           <term><constant>-ECHILD</constant></term>
 139
 140           <listitem><para>The bus was created in a different process.</para></listitem>
 141         </varlistentry>
 142       </variablelist>
 143     </refsect2>
 144   </refsect1>
 145
 146   <xi:include href="libsystemd-pkgconfig.xml" />
 147
 148   <refsect1>
 149     <title>See Also</title>
 150
 151     <para>
 152       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 156       <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 160     </para>
 161   </refsect1>
 162
 163 </refentry>