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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2013 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_bus_message_get_monotonic_usec" conditional="ENABLE_KDBUS">
<refentryinfo>
<title>sd_bus_message_get_monotonic_usec</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_message_get_monotonic_usec</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_message_get_monotonic_usec</refname>
<refname>sd_bus_message_get_realtime_usec</refname>
<refname>sd_bus_message_get_seqnum</refname>
<refpurpose>Retrieve the sender timestamps and sequence number of a message</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_message_get_monotonic_usec</function></funcdef>
<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_message_get_realtime_usec</function></funcdef>
<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_message_get_seqnum</function></funcdef>
<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
<paramdef>uint64_t *<parameter>seqnum</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_message_get_monotonic_usec()</function>
returns the monotonic timestamp of the time the
message was sent. This value is in microseconds since
the <literal>CLOCK_MONOTONIC</literal> epoch, see
<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para>
<para>Similar,
<function>sd_bus_message_get_realtime_usec()</function>
returns the realtime (wallclock) timestamp of the time
the message was sent. This value is in microseconds
since Jan 1st, 1970, i.e. in the
<literal>CLOCK_REALTIME</literal> clock.</para>
<para><function>sd_bus_message_get_seqnum()</function>
returns the kernel-assigned sequence number of the
message. The kernel assigns a global, monotonically
increasing sequence number to all messages transmitted
on the local system, at the time the message was
sent. This sequence number is useful for determining
message send order, even across different busses of
the local system. The sequence number combined with
the boot ID of the system (as returned by
<citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
is a suitable globally unique identifier for bus
messages.</para>
<para>Note that the sending order and receiving order
of messages might differ, in particular for broadcast
messages. This means that the sequence number and the
timestamps of messages a client reads are not
necessarily monotonically increasing.</para>
<para>These timestamps and the sequence number are
attached to each message by the kernel and cannot be
manipulated by the sender.</para>
<para>Note that these timestamps are only available on
some bus transports, and only after support for them
has been negotiated with the
<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>
call.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, these calls return 0 or a positive
integer. On failure, these calls return a negative
errno-style error code.</para>
<para>On success, the timestamp or sequence number is
returned in the specified 64-bit unsigned integer
variable.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><varname>-EINVAL</varname></term>
<listitem><para>A specified parameter
is invalid.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>-ENODATA</varname></term>
<listitem><para>No timestamp or
sequence number information is
attached to the passed message. This
error is returned if the underlying
transport does not support
timestamping or assigning of sequence
numbers, or if this feature has not
been negotiated with
<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>The
<function>sd_bus_message_get_monotonic_usec()</function>,
<function>sd_bus_message_get_realtime_usec()</function>,
and <function>sd_bus_message_get_seqnum()</function>
interfaces are available as a shared library, which
can be compiled and linked to with the
<constant>libsystemd</constant> <citerefentry><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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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