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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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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 | ||
6a70f3aa | 24 | <refentry id="sd-id128" |
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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> | |
2b044526 | 50 | <refname>SD_ID128_MAKE_STR</refname> |
3dbea941 | 51 | <refname>SD_ID128_NULL</refname> |
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52 | <refname>SD_ID128_CONST_STR</refname> |
53 | <refname>SD_ID128_FORMAT_STR</refname> | |
54 | <refname>SD_ID128_FORMAT_VAL</refname> | |
55 | <refname>sd_id128_equal</refname> | |
3dbea941 | 56 | <refname>sd_id128_is_null</refname> |
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57 | <refpurpose>APIs for processing 128-bit IDs</refpurpose> |
58 | </refnamediv> | |
59 | ||
60 | <refsynopsisdiv> | |
61 | <funcsynopsis> | |
62 | <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> | |
63 | </funcsynopsis> | |
64 | ||
65 | <cmdsynopsis> | |
66 | <command>pkg-config --cflags --libs libsystemd</command> | |
67 | </cmdsynopsis> | |
68 | ||
69 | </refsynopsisdiv> | |
70 | ||
71 | <refsect1> | |
72 | <title>Description</title> | |
73 | ||
74 | <para><filename>sd-id128.h</filename> provides APIs to process and | |
75 | generate 128-bit ID values. The 128-bit ID values processed and | |
76 | generated by these APIs are a generalization of OSF UUIDs as | |
77 | defined by <ulink url="https://tools.ietf.org/html/rfc4122">RFC | |
78 | 4122</ulink> but use a simpler string format. These functions | |
79 | impose no structure on the used IDs, much unlike OSF UUIDs or | |
80 | Microsoft GUIDs, but are fully compatible with those types of IDs. | |
81 | </para> | |
82 | ||
83 | <para>See | |
84 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
85 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
86 | and | |
87 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
88 | for more information about the implemented functions.</para> | |
89 | ||
90 | <para>A 128-bit ID is implemented as the following | |
91 | union type:</para> | |
92 | ||
93 | <programlisting>typedef union sd_id128 { | |
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94 | uint8_t bytes[16]; |
95 | uint64_t qwords[2]; | |
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96 | } sd_id128_t;</programlisting> |
97 | ||
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98 | <para>This union type allows accessing the 128-bit ID as 16 |
99 | separate bytes or two 64-bit words. It is generally safer to | |
100 | access the ID components by their 8-bit array to avoid endianness | |
101 | issues. This union is intended to be passed call-by-value (as | |
102 | opposed to call-by-reference) and may be directly manipulated by | |
103 | clients.</para> | |
104 | ||
105 | <para>A couple of macros are defined to denote and decode 128-bit | |
106 | IDs:</para> | |
107 | ||
108 | <para><function>SD_ID128_MAKE()</function> may be used to denote a | |
109 | constant 128-bit ID in source code. A commonly used idiom is to | |
110 | assign a name to a 128-bit ID using this macro:</para> | |
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 | ||
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114 | <para><function>SD_ID128_NULL</function> may be used to refer to the 128bit ID consisting of only NUL |
115 | bytes.</para> | |
116 | ||
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117 | <para><function>SD_ID128_MAKE_STR()</function> is similar to <function>SD_ID128_MAKE()</function>, but creates a |
118 | <type>const char*</type> expression that can be conveniently used in message formats and such:</para> | |
119 | ||
120 | <programlisting>#include <stdio.h> | |
121 | #define SD_MESSAGE_COREDUMP_STR SD_ID128_MAKE_STR(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1) | |
122 | ||
123 | int main(int argc, char **argv) { | |
124 | puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR); | |
125 | } | |
126 | </programlisting> | |
127 | ||
128 | ||
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129 | <para><function>SD_ID128_CONST_STR()</function> may be used to |
130 | convert constant 128-bit IDs into constant strings for output. The | |
131 | following example code will output the string | |
132 | "fc2e22bc6ee647b6b90729ab34a250b1":</para> | |
133 | <programlisting>int main(int argc, char *argv[]) { | |
2b044526 | 134 | puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP)); |
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135 | }</programlisting> |
136 | ||
3dbea941 | 137 | <para><function>SD_ID128_FORMAT_STR()</function> and |
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138 | <function>SD_ID128_FORMAT_VAL()</function> may be used to format a |
139 | 128-bit ID in a | |
140 | <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
141 | format string, as shown in the following example:</para> | |
142 | ||
143 | <programlisting>int main(int argc, char *argv[]) { | |
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144 | sd_id128_t id; |
145 | id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
146 | printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id)); | |
147 | return 0; | |
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148 | }</programlisting> |
149 | ||
798d3a52 | 150 | <para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para> |
12355095 | 151 | |
798d3a52 | 152 | <programlisting>int main(int argc, char *argv[]) { |
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153 | sd_id128_t a, b, c; |
154 | a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
155 | b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e); | |
156 | c = a; | |
157 | assert(sd_id128_equal(a, c)); | |
158 | assert(!sd_id128_equal(a, b)); | |
159 | return 0; | |
160 | }</programlisting> | |
161 | ||
162 | <para>Use <function>sd_id128_is_null()</function> to check if an 128bit ID consists of only NUL bytes:</para> | |
163 | ||
164 | <programlisting>int main(int argc, char *argv[]) { | |
165 | assert(sd_id128_is_null(SD_ID128_NULL)); | |
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166 | }</programlisting> |
167 | ||
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168 | <para>Note that new, randomized IDs may be generated with |
169 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s | |
b22319ea | 170 | <option>--new-id128</option> option.</para> |
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171 | </refsect1> |
172 | ||
173 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
174 | ||
175 | <refsect1> | |
176 | <title>See Also</title> | |
177 | <para> | |
178 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
179 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
180 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
181 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
182 | <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
183 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
184 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
185 | <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
186 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
187 | </para> | |
188 | </refsect1> | |
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189 | |
190 | </refentry> |