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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">
4
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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>