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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 | ||
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 | ||
26 | <refentryinfo> | |
27 | <title>sd-id128</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-id128</refentrytitle> | |
cb07866b | 42 | <manvolnum>3</manvolnum> |
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43 | </refmeta> |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd-id128</refname> | |
47 | <refname>sd_id128_t</refname> | |
48 | <refname>SD_ID128_MAKE</refname> | |
183de6d7 | 49 | <refname>SD_ID128_CONST_STR</refname> |
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50 | <refname>SD_ID128_FORMAT_STR</refname> |
51 | <refname>SD_ID128_FORMAT_VAL</refname> | |
52 | <refname>sd_id128_equal</refname> | |
53 | <refpurpose>APIs for processing 128 bit IDs</refpurpose> | |
54 | </refnamediv> | |
55 | ||
56 | <refsynopsisdiv> | |
57 | <funcsynopsis> | |
58 | <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> | |
59 | </funcsynopsis> | |
60 | ||
61 | <cmdsynopsis> | |
62 | <command>pkg-config --cflags --libs libsystemd-id128</command> | |
63 | </cmdsynopsis> | |
64 | ||
65 | </refsynopsisdiv> | |
66 | ||
67 | <refsect1> | |
68 | <title>Description</title> | |
69 | ||
70 | <para><filename>sd-id128.h</filename> provides APIs to | |
71 | process and generate 128 bit ID values. The 128 bit ID | |
72 | values processed and generated by these APIs are a | |
73 | generalization of OSF UUIDs as defined by <ulink | |
74 | url="http://tools.ietf.org/html/rfc4122">RFC | |
75 | 4122</ulink>, though use a simpler string | |
76 | formatting. These functions impose no structure on the | |
77 | used IDs, much unlike OSF UUIDs or Microsoft GUIDs, | |
78 | but are fully compatible with those types of IDs. | |
79 | </para> | |
80 | ||
81 | <para>See | |
a4023a43 LP |
82 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
83 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> and | |
84 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
bfc79e34 PM |
85 | for more information about the implemented |
86 | functions.</para> | |
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87 | |
88 | <para>A 128 bit ID is implemented as the following | |
89 | union type:</para> | |
90 | ||
91 | <programlisting>typedef union sd_id128 { | |
92 | uint8_t bytes[16]; | |
93 | uint64_t qwords[2]; | |
94 | } sd_id128_t;</programlisting> | |
95 | ||
96 | <para>This union type allows accessing the 128 bit ID | |
bfc79e34 | 97 | as 16 separate bytes or two 64 bit words. It is generally |
12355095 | 98 | safer to access the ID components by their 8 bit array |
40b90434 | 99 | to avoid endianness issues. This union is intended to |
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100 | be passed call-by-value (as opposed to |
101 | call-by-reference) and may be directly manipulated by | |
102 | clients.</para> | |
103 | ||
104 | <para>A couple of macros are defined to denote and | |
105 | decode 128 bit IDs:</para> | |
106 | ||
107 | <para><function>SD_ID128_MAKE()</function> may be used | |
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108 | to denote a constant 128 bit ID in source code. A |
109 | commonly used idiom is to assign a name to a 128 bit | |
110 | ID using this macro:</para> | |
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111 | |
112 | <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> | |
113 | ||
183de6d7 | 114 | <para><function>SD_ID128_CONST_STR()</function> may be |
1707b36c | 115 | used to convert constant 128bit IDs into constant |
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116 | strings for output. The following example code will |
117 | output the string | |
118 | "fc2e22bc6ee647b6b90729ab34a250b1":</para> | |
119 | <programlisting>int main(int argc, char *argv[]) { | |
120 | puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP)); | |
121 | }</programlisting> | |
122 | ||
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123 | <para><function>SD_ID128_FORMAT_STR</function> and |
124 | <function>SD_ID128_FORMAT_VAL()</function> may be used | |
125 | to format a 128 bit ID in a | |
126 | <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
127 | format string, as shown in the following | |
128 | example:</para> | |
129 | ||
130 | <programlisting>int main(int argc, char *argv[]) { | |
131 | sd_id128_t id; | |
132 | id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
133 | printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id)); | |
134 | return 0; | |
135 | }</programlisting> | |
136 | ||
137 | <para>Use <function>sd_id128_equal()</function> to compare two 128 bit IDs:</para> | |
138 | ||
139 | <programlisting>int main(int argc, char *argv[]) { | |
140 | sd_id128_t a, b, c; | |
141 | a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
142 | b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e); | |
143 | c = a; | |
144 | assert(sd_id128_equal(a, c)); | |
145 | assert(!sd_id128_equal(a, b)); | |
146 | return 0; | |
147 | }</programlisting> | |
148 | ||
149 | <para>Note that new, randomized IDs may be generated | |
150 | with | |
151 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s | |
bfc79e34 | 152 | <literal>--new-id</literal> option.</para> |
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153 | </refsect1> |
154 | ||
155 | <refsect1> | |
156 | <title>Notes</title> | |
157 | ||
bfc79e34 | 158 | <para>These APIs are implemented as a shared library, |
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159 | which can be compiled and linked to with the |
160 | <literal>libsystemd-id128</literal> | |
161 | <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
162 | file.</para> | |
163 | ||
164 | </refsect1> | |
165 | ||
166 | <refsect1> | |
167 | <title>See Also</title> | |
168 | <para> | |
169 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
170 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
171 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
a4023a43 | 172 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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173 | <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
174 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
175 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
176 | <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
177 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
178 | </para> | |
179 | </refsect1> | |
180 | ||
181 | </refentry> |