man/sd_bus_message_get_monotonic_usec.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   8   Copyright 2013 Lennart Poettering
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  23
  24 <refentry id="sd_bus_message_get_monotonic_usec">
  25
  26         <refentryinfo>
  27                 <title>sd_bus_message_get_monotonic_usec</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_message_get_monotonic_usec</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_bus_message_get_monotonic_usec</refname>
  47                 <refname>sd_bus_message_get_realtime_usec</refname>
  48                 <refname>sd_bus_message_get_seqnum</refname>
  49                 <refpurpose>Retrieve the sender timestamps and sequence number of a message</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <funcsynopsis>
  54                         <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  55
  56                         <funcprototype>
  57                                 <funcdef>int <function>sd_bus_message_get_monotonic_usec</function></funcdef>
  58                                 <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  59                                 <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  60                         </funcprototype>
  61
  62                         <funcprototype>
  63                                 <funcdef>int <function>sd_bus_message_get_realtime_usec</function></funcdef>
  64                                 <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  65                                 <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  66                         </funcprototype>
  67
  68                         <funcprototype>
  69                                 <funcdef>int <function>sd_bus_message_get_seqnum</function></funcdef>
  70                                 <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  71                                 <paramdef>uint64_t *<parameter>seqnum</parameter></paramdef>
  72                         </funcprototype>
  73                 </funcsynopsis>
  74         </refsynopsisdiv>
  75
  76         <refsect1>
  77                 <title>Description</title>
  78
  79                 <para><function>sd_bus_message_get_monotonic_usec()</function>
  80                 returns the monotonic timestamp of the time the
  81                 message was sent. This value is in microseconds since
  82                 the <literal>CLOCK_MONOTONIC</literal> epoch, see
  83                 <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  84                 for details.</para>
  85
  86                 <para>Similar,
  87                 <function>sd_bus_message_get_realtime_usec()</function>
  88                 returns the realtime (wallclock) timestamp of the time
  89                 the message was sent. This value is in microseconds
  90                 since Jan 1st, 1970, i.e. in the
  91                 <literal>CLOCK_REALTIME</literal> clock.</para>
  92
  93                 <para><function>sd_bus_message_get_seqnum()</function>
  94                 returns the kernel-assigned sequence number of the
  95                 message. The kernel assigns a global monotonically increasing
  96                 sequence number to all messages sent on the local
  97                 system. This sequence number is useful for determining
  98                 message send order, even across different busses of
  99                 the local system. The sequence number combined with
 100                 the boot ID of the system (as returned by
 101                 <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
 102                 is a suitable globally unique identifier for bus
 103                 messages.</para>
 104
 105                 <para>These timestamps and the sequence number are
 106                 attached to each message by the kernel and cannot be
 107                 manipulated by the sender.</para>
 108
 109                 <para>Note that these timestamps are only available on
 110                 some bus transports, and only after support for them
 111                 has been negotiated with the
 112                 <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 113                 call.</para>
 114         </refsect1>
 115
 116         <refsect1>
 117                 <title>Return Value</title>
 118
 119                 <para>On success, these calls return 0 or a positive
 120                 integer. On failure, these calls return a negative
 121                 errno-style error code.</para>
 122
 123                 <para>On success, the timestamp or sequence number is
 124                 returned in the specified 64-bit unsigned integer
 125                 variable.</para>
 126         </refsect1>
 127
 128         <refsect1>
 129                 <title>Errors</title>
 130
 131                 <para>Returned errors may indicate the following problems:</para>
 132
 133                 <variablelist>
 134                         <varlistentry>
 135                                 <term><varname>-EINVAL</varname></term>
 136
 137                                 <listitem><para>A specified parameter
 138                                 is invalid.</para></listitem>
 139                         </varlistentry>
 140
 141                         <varlistentry>
 142                                 <term><varname>-ENODATA</varname></term>
 143
 144                                 <listitem><para>No timestamp or
 145                                 sequence number information is
 146                                 attached to the passed message. This
 147                                 error is returned if the underlying
 148                                 transport does not support
 149                                 timestamping or assigning of sequence
 150                                 numbers, or if this feature has not
 151                                 been negotiated with
 152                                 <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 153                         </varlistentry>
 154                 </variablelist>
 155         </refsect1>
 156
 157         <refsect1>
 158                 <title>Notes</title>
 159
 160                 <para>The
 161                 <function>sd_bus_message_get_monotonic_usec()</function>,
 162                 <function>sd_bus_message_get_realtime_usec()</function>,
 163                 and <function>sd_bus_message_get_seqnum()</function>
 164                 interfaces are available as a shared library, which
 165                 can be compiled and linked to with the
 166                 <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 167                 file.</para>
 168         </refsect1>
 169
 170         <refsect1>
 171                 <title>See Also</title>
 172
 173                 <para>
 174                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 175                         <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 176                         <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 177                         <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 178                         <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 179                         <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 180                 </para>
 181         </refsect1>
 182
 183 </refentry>