man/sd_bus_negotiate_fds.xml

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  23
  24 <refentry id="sd_bus_negotiate_fds" conditional="ENABLE_KDBUS">
  25
  26   <refentryinfo>
  27     <title>sd_bus_negotiate_fds</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_bus_negotiate_fds</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_bus_negotiate_fds</refname>
  47     <refname>sd_bus_negotiate_timestamps</refname>
  48     <refname>sd_bus_negotiate_creds</refname>
  49
  50     <refpurpose>Control feature negotiation on bus connections</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <funcsynopsis>
  55       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  56
  57       <funcprototype>
  58         <funcdef>int <function>sd_bus_negotiate_fds</function></funcdef>
  59         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  60         <paramdef>int <parameter>b</parameter></paramdef>
  61       </funcprototype>
  62
  63       <funcprototype>
  64         <funcdef>int <function>sd_bus_negotiate_timestamp</function></funcdef>
  65         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  66         <paramdef>int <parameter>b</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
  71         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  72         <paramdef>int <parameter>b</parameter></paramdef>
  73         <paramdef>uint64_t <parameter>flags</parameter></paramdef>
  74       </funcprototype>
  75     </funcsynopsis>
  76   </refsynopsisdiv>
  77
  78   <refsect1>
  79     <title>Description</title>
  80
  81     <para><function>sd_bus_negotiate_fds()</function> controls whether
  82     file descriptor passing shall be negotiated for the specified bus
  83     connection. It takes a bus object and a boolean, which, when true,
  84     enables file descriptor passing, and, when false, disables it. Note
  85     that not all transports and servers support file descriptor
  86     passing. To find out whether file descriptor passing is available
  87     after negotiation, use
  88     <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  89     and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file
  90     descriptor passing is always enabled for both sending and
  91     receiving or for neither, but never only in one direction. By
  92     default, file descriptor passing is negotiated for all
  93     connections.</para>
  94
  95     <para>Note that when bus activation is used, it is highly
  96     recommended to set the <option>AcceptFileDescriptors=</option>
  97     setting in the <filename>.busname</filename> unit file to the same
  98     setting as negotiated by the program ultimately activated. By
  99     default, file descriptor passing is enabled for both.</para>
 100
 101     <para><function>sd_bus_negotiate_timestamps()</function> controls
 102     whether implicit sender timestamps shall be attached automatically
 103     to all incoming messages. Takes a bus object and a boolean, which,
 104     when true, enables timestamping, and, when false, disables it. If
 105     this is disabled,
 106     <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 107     <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 108     <citerefentry><refentrytitle>sd_bus_message_get_seqno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 109     fail with <constant>-ENODATA</constant> on incoming messages. Note
 110     that not all transports support timestamping of messages. On local
 111     transports, the timestamping is applied by the kernel and cannot
 112     be manipulated by userspace. By default, message timestamping is
 113     not negotiated for all connections.</para>
 114
 115     <para><function>sd_bus_negotiate_creds()</function> controls
 116     whether implicit sender credentials shall be attached
 117     automatically to all incoming messages. Takes a bus object, a
 118     boolean indicating whether to enable or disable the credential
 119     parts encoded in the bit mask value argument. Note that not all
 120     transports support attaching sender credentials to messages, or do
 121     not support all types of sender credential parameters, or might
 122     suppress them under certain circumstances for individual
 123     messages. On local transports, the sender credentials are attached
 124     by the kernel and cannot be manipulated by userspace. By default,
 125     no sender credentials are attached.</para>
 126
 127     <para>The <function>sd_bus_negotiate_fds()</function> function may
 128     be called only before the connection has been started with
 129     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
 130     <function>sd_bus_negotiate_timestamp()</function> and
 131     <function>sd_bus_negotiate_creds()</function> also may be called
 132     after a connection has been set up. Note that when operating on a
 133     connection that is shared between multiple components of the same
 134     program (for example via
 135     <citerefentry><refentrytitle>sd_bus_default</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
 136     it is highly recommended to only enable additional per message
 137     metadata fields, but never disable them again, in order not to
 138     disable functionality needed by other components.</para>
 139   </refsect1>
 140
 141   <refsect1>
 142     <title>Return Value</title>
 143
 144     <para>On success, these functions returns 0 or a
 145     positive integer. On failure, they return a negative errno-style
 146     error code.</para>
 147   </refsect1>
 148
 149   <refsect1>
 150     <title>Errors</title>
 151
 152     <para>Returned errors may indicate the following problems:</para>
 153
 154     <variablelist>
 155       <varlistentry>
 156         <term><constant>-EPERM</constant></term>
 157
 158         <listitem><para>The bus connection has already been started.</para></listitem>
 159       </varlistentry>
 160     </variablelist>
 161   </refsect1>
 162
 163   <refsect1>
 164     <title>Notes</title>
 165
 166     <para><function>sd_bus_negotiate_fs()</function> and the other
 167     functions described here are available as a shared library, which
 168     can be compiled and linked to with the
 169     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 170     file.</para>
 171   </refsect1>
 172
 173   <refsect1>
 174     <title>See Also</title>
 175
 176     <para>
 177       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 179       <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 180       <citerefentry><refentrytitle>sd_bus_message_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 181       <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 182       <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>systemd.busname</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 184     </para>
 185   </refsect1>
 186
 187 </refentry>