1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
|
<?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">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="sd_bus_message_get_monotonic_usec"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_message_get_monotonic_usec</title>
<productname>systemd</productname>
</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
<constant>CLOCK_MONOTONIC</constant> epoch, see
<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para>
<para>Similarly,
<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 <constant>CLOCK_REALTIME</constant> 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 buses 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><constant>-EINVAL</constant></term>
<listitem><para>A specified parameter is
invalid.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENODATA</constant></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>
<xi:include href="libsystemd-pkgconfig.xml" />
<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>
|
