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<refentry id="sd_bus_negotiate_fds">

<refentryinfo>

<title>sd_bus_negotiate_fds</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</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>

<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>

</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>Note that when bus activation is used, it is highly

recommended to set the <option>AcceptFileDescriptors=</option>

setting in the <filename>.busname</filename> unit file to the same

setting as negotiated by the program ultimately activated. By

default, file descriptor passing is enabled for both.</para>

<para><function>sd_bus_negotiate_timestamps()</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 not all transports

support timestamping of messages. Specifically, timestamping is

only available on the kdbus transport, but not on dbus1. The

timestamping is applied by the kernel and cannot be manipulated by

userspace. 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, 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, implicit sender credentials on messages

are only fully supported on kdbus transports, and dbus1 only

supports <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender

credentials are attached by the kernel and cannot be manipulated

by userspace, and are thus 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>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 returns 0 or a

positive integer. On failure, they return a negative errno-style

error code.</para>

</refsect1>

<refsect1>

<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>

</variablelist>

</refsect1>

<refsect1>

<title>Notes</title>

<para><function>sd_bus_negotiate_fds()</function> and the other

functions described here are available as a shared library, which

can be compiled and linked to with the

<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</para>

</refsect1>

<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_message_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>,

<citerefentry><refentrytitle>systemd.busname</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>