chiark / gitweb /
man: bring machinectl man page up-to-date
[elogind.git] / man / sd-id128.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
5 <!--
6   This file is part of systemd.
7
8   Copyright 2012 Lennart Poettering
9
10   systemd is free software; you can redistribute it and/or modify it
11   under the terms of the GNU Lesser General Public License as published by
12   the Free Software Foundation; either version 2.1 of the License, or
13   (at your option) any later version.
14
15   systemd is distributed in the hope that it will be useful, but
16   WITHOUT ANY WARRANTY; without even the implied warranty of
17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18   Lesser General Public License for more details.
19
20   You should have received a copy of the GNU Lesser General Public License
21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
22 -->
23
24 <refentry id="sd-id128"
25         xmlns:xi="http://www.w3.org/2001/XInclude">
26
27         <refentryinfo>
28                 <title>sd-id128</title>
29                 <productname>systemd</productname>
30
31                 <authorgroup>
32                         <author>
33                                 <contrib>Developer</contrib>
34                                 <firstname>Lennart</firstname>
35                                 <surname>Poettering</surname>
36                                 <email>lennart@poettering.net</email>
37                         </author>
38                 </authorgroup>
39         </refentryinfo>
40
41         <refmeta>
42                 <refentrytitle>sd-id128</refentrytitle>
43                 <manvolnum>3</manvolnum>
44         </refmeta>
45
46         <refnamediv>
47                 <refname>sd-id128</refname>
48                 <refname>sd_id128_t</refname>
49                 <refname>SD_ID128_MAKE</refname>
50                 <refname>SD_ID128_CONST_STR</refname>
51                 <refname>SD_ID128_FORMAT_STR</refname>
52                 <refname>SD_ID128_FORMAT_VAL</refname>
53                 <refname>sd_id128_equal</refname>
54                 <refpurpose>APIs for processing 128-bit IDs</refpurpose>
55         </refnamediv>
56
57         <refsynopsisdiv>
58                 <funcsynopsis>
59                         <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>
60                 </funcsynopsis>
61
62                 <cmdsynopsis>
63                         <command>pkg-config --cflags --libs libsystemd</command>
64                 </cmdsynopsis>
65
66         </refsynopsisdiv>
67
68         <refsect1>
69                 <title>Description</title>
70
71                 <para><filename>sd-id128.h</filename> provides APIs to
72                 process and generate 128-bit ID values. The 128-bit ID
73                 values processed and generated by these APIs are a
74                 generalization of OSF UUIDs as defined by <ulink
75                 url="https://tools.ietf.org/html/rfc4122">RFC
76                 4122</ulink> but use a simpler string
77                 format. These functions impose no structure on the
78                 used IDs, much unlike OSF UUIDs or Microsoft GUIDs,
79                 but are fully compatible with those types of IDs.
80                 </para>
81
82                 <para>See
83                 <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
84                 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
85                 <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
86                 for more information about the implemented
87                 functions.</para>
88
89                 <para>A 128-bit ID is implemented as the following
90                 union type:</para>
91
92                 <programlisting>typedef union sd_id128 {
93         uint8_t bytes[16];
94         uint64_t qwords[2];
95 } sd_id128_t;</programlisting>
96
97                 <para>This union type allows accessing the 128-bit ID
98                 as 16 separate bytes or two 64-bit words. It is generally
99                 safer to access the ID components by their 8-bit array
100                 to avoid endianness issues. This union is intended to
101                 be passed call-by-value (as opposed to
102                 call-by-reference) and may be directly manipulated by
103                 clients.</para>
104
105                 <para>A couple of macros are defined to denote and
106                 decode 128-bit IDs:</para>
107
108                 <para><function>SD_ID128_MAKE()</function> may be used
109                 to denote a constant 128-bit ID in source code. A
110                 commonly used idiom is to assign a name to a 128-bit
111                 ID using this macro:</para>
112
113                 <programlisting>#define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)</programlisting>
114
115                 <para><function>SD_ID128_CONST_STR()</function> may be
116                 used to convert constant 128-bit IDs into constant
117                 strings for output. The following example code will
118                 output the string
119                 "fc2e22bc6ee647b6b90729ab34a250b1":</para>
120                 <programlisting>int main(int argc, char *argv[]) {
121         puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
122 }</programlisting>
123
124                 <para><function>SD_ID128_FORMAT_STR</function> and
125                 <function>SD_ID128_FORMAT_VAL()</function> may be used
126                 to format a 128-bit ID in a
127                 <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
128                 format string, as shown in the following
129                 example:</para>
130
131                 <programlisting>int main(int argc, char *argv[]) {
132         sd_id128_t id;
133         id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
134         printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
135         return 0;
136 }</programlisting>
137
138                 <para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para>
139
140                 <programlisting>int main(int argc, char *argv[]) {
141         sd_id128_t a, b, c;
142         a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
143         b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
144         c = a;
145         assert(sd_id128_equal(a, c));
146         assert(!sd_id128_equal(a, b));
147         return 0;
148 }</programlisting>
149
150                 <para>Note that new, randomized IDs may be generated
151                 with
152                 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
153                 <option>--new-id</option> option.</para>
154         </refsect1>
155
156         <xi:include href="libsystemd-pkgconfig.xml" />
157
158         <refsect1>
159                 <title>See Also</title>
160                 <para>
161                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
162                         <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
163                         <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
164                         <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
165                         <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
166                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
167                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
168                         <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
169                         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
170                 </para>
171         </refsect1>
172
173 </refentry>