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[elogind.git] / 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">
4
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8   Copyright 2013 Lennart Poettering
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23
24 <refentry id="sd_bus_message_get_monotonic_usec" conditional="ENABLE_KDBUS">
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
96                 increasing sequence number to all messages transmitted
97                 on the local system, at the time the message was
98                 sent. This sequence number is useful for determining
99                 message send order, even across different busses of
100                 the local system. The sequence number combined with
101                 the boot ID of the system (as returned by
102                 <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
103                 is a suitable globally unique identifier for bus
104                 messages.</para>
105
106                 <para>Note that the sending order and receiving order
107                 of messages might differ, in particular for broadcast
108                 messages. This means that the sequence number and the
109                 timestamps of messages a client reads are not
110                 necessarily monotonically increasing.</para>
111
112                 <para>These timestamps and the sequence number are
113                 attached to each message by the kernel and cannot be
114                 manipulated by the sender.</para>
115
116                 <para>Note that these timestamps are only available on
117                 some bus transports, and only after support for them
118                 has been negotiated with the
119                 <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>
120                 call.</para>
121         </refsect1>
122
123         <refsect1>
124                 <title>Return Value</title>
125
126                 <para>On success, these calls return 0 or a positive
127                 integer. On failure, these calls return a negative
128                 errno-style error code.</para>
129
130                 <para>On success, the timestamp or sequence number is
131                 returned in the specified 64-bit unsigned integer
132                 variable.</para>
133         </refsect1>
134
135         <refsect1>
136                 <title>Errors</title>
137
138                 <para>Returned errors may indicate the following problems:</para>
139
140                 <variablelist>
141                         <varlistentry>
142                                 <term><varname>-EINVAL</varname></term>
143
144                                 <listitem><para>A specified parameter
145                                 is invalid.</para></listitem>
146                         </varlistentry>
147
148                         <varlistentry>
149                                 <term><varname>-ENODATA</varname></term>
150
151                                 <listitem><para>No timestamp or
152                                 sequence number information is
153                                 attached to the passed message. This
154                                 error is returned if the underlying
155                                 transport does not support
156                                 timestamping or assigning of sequence
157                                 numbers, or if this feature has not
158                                 been negotiated with
159                                 <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
160                         </varlistentry>
161                 </variablelist>
162         </refsect1>
163
164         <refsect1>
165                 <title>Notes</title>
166
167                 <para>The
168                 <function>sd_bus_message_get_monotonic_usec()</function>,
169                 <function>sd_bus_message_get_realtime_usec()</function>,
170                 and <function>sd_bus_message_get_seqnum()</function>
171                 interfaces are available as a shared library, which
172                 can be compiled and linked to with the
173                 <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
174                 file.</para>
175         </refsect1>
176
177         <refsect1>
178                 <title>See Also</title>
179
180                 <para>
181                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
182                         <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
183                         <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
184                         <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
185                         <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
186                         <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
187                 </para>
188         </refsect1>
189
190 </refentry>