systemd/man/sd_bus_message_get_monotonic_usec.xml

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        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<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 &lt;systemd/sd-bus.h&gt;</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>