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12355095 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
12355095 | 5 | |
6a70f3aa | 6 | <refentry id="sd-id128" |
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7 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
8 | ||
9 | <refentryinfo> | |
10 | <title>sd-id128</title> | |
11 | <productname>systemd</productname> | |
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12 | </refentryinfo> |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>sd-id128</refentrytitle> | |
16 | <manvolnum>3</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>sd-id128</refname> | |
21 | <refname>sd_id128_t</refname> | |
22 | <refname>SD_ID128_MAKE</refname> | |
2b044526 | 23 | <refname>SD_ID128_MAKE_STR</refname> |
3dbea941 | 24 | <refname>SD_ID128_NULL</refname> |
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25 | <refname>SD_ID128_CONST_STR</refname> |
26 | <refname>SD_ID128_FORMAT_STR</refname> | |
27 | <refname>SD_ID128_FORMAT_VAL</refname> | |
28 | <refname>sd_id128_equal</refname> | |
3dbea941 | 29 | <refname>sd_id128_is_null</refname> |
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30 | <refpurpose>APIs for processing 128-bit IDs</refpurpose> |
31 | </refnamediv> | |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
35 | <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> | |
36 | </funcsynopsis> | |
37 | ||
38 | <cmdsynopsis> | |
39 | <command>pkg-config --cflags --libs libsystemd</command> | |
40 | </cmdsynopsis> | |
41 | ||
42 | </refsynopsisdiv> | |
43 | ||
44 | <refsect1> | |
45 | <title>Description</title> | |
46 | ||
47 | <para><filename>sd-id128.h</filename> provides APIs to process and | |
48 | generate 128-bit ID values. The 128-bit ID values processed and | |
49 | generated by these APIs are a generalization of OSF UUIDs as | |
50 | defined by <ulink url="https://tools.ietf.org/html/rfc4122">RFC | |
51 | 4122</ulink> but use a simpler string format. These functions | |
52 | impose no structure on the used IDs, much unlike OSF UUIDs or | |
53 | Microsoft GUIDs, but are fully compatible with those types of IDs. | |
54 | </para> | |
55 | ||
56 | <para>See | |
57 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
58 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
59 | and | |
60 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
61 | for more information about the implemented functions.</para> | |
62 | ||
63 | <para>A 128-bit ID is implemented as the following | |
64 | union type:</para> | |
65 | ||
66 | <programlisting>typedef union sd_id128 { | |
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67 | uint8_t bytes[16]; |
68 | uint64_t qwords[2]; | |
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69 | } sd_id128_t;</programlisting> |
70 | ||
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71 | <para>This union type allows accessing the 128-bit ID as 16 |
72 | separate bytes or two 64-bit words. It is generally safer to | |
73 | access the ID components by their 8-bit array to avoid endianness | |
74 | issues. This union is intended to be passed call-by-value (as | |
75 | opposed to call-by-reference) and may be directly manipulated by | |
76 | clients.</para> | |
77 | ||
78 | <para>A couple of macros are defined to denote and decode 128-bit | |
79 | IDs:</para> | |
80 | ||
81 | <para><function>SD_ID128_MAKE()</function> may be used to denote a | |
82 | constant 128-bit ID in source code. A commonly used idiom is to | |
83 | assign a name to a 128-bit ID using this macro:</para> | |
84 | ||
85 | <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> | |
86 | ||
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87 | <para><function>SD_ID128_NULL</function> may be used to refer to the 128bit ID consisting of only NUL |
88 | bytes.</para> | |
89 | ||
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90 | <para><function>SD_ID128_MAKE_STR()</function> is similar to <function>SD_ID128_MAKE()</function>, but creates a |
91 | <type>const char*</type> expression that can be conveniently used in message formats and such:</para> | |
92 | ||
93 | <programlisting>#include <stdio.h> | |
94 | #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) | |
95 | ||
96 | int main(int argc, char **argv) { | |
97 | puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR); | |
98 | } | |
99 | </programlisting> | |
100 | ||
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101 | <para><function>SD_ID128_CONST_STR()</function> may be used to |
102 | convert constant 128-bit IDs into constant strings for output. The | |
103 | following example code will output the string | |
104 | "fc2e22bc6ee647b6b90729ab34a250b1":</para> | |
105 | <programlisting>int main(int argc, char *argv[]) { | |
2b044526 | 106 | puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP)); |
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107 | }</programlisting> |
108 | ||
3dbea941 | 109 | <para><function>SD_ID128_FORMAT_STR()</function> and |
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110 | <function>SD_ID128_FORMAT_VAL()</function> may be used to format a |
111 | 128-bit ID in a | |
112 | <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
113 | format string, as shown in the following example:</para> | |
114 | ||
115 | <programlisting>int main(int argc, char *argv[]) { | |
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116 | sd_id128_t id; |
117 | id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
118 | printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id)); | |
119 | return 0; | |
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120 | }</programlisting> |
121 | ||
798d3a52 | 122 | <para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para> |
12355095 | 123 | |
798d3a52 | 124 | <programlisting>int main(int argc, char *argv[]) { |
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125 | sd_id128_t a, b, c; |
126 | a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07); | |
127 | b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e); | |
128 | c = a; | |
129 | assert(sd_id128_equal(a, c)); | |
130 | assert(!sd_id128_equal(a, b)); | |
131 | return 0; | |
132 | }</programlisting> | |
133 | ||
134 | <para>Use <function>sd_id128_is_null()</function> to check if an 128bit ID consists of only NUL bytes:</para> | |
135 | ||
136 | <programlisting>int main(int argc, char *argv[]) { | |
137 | assert(sd_id128_is_null(SD_ID128_NULL)); | |
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138 | }</programlisting> |
139 | ||
798d3a52 | 140 | <para>Note that new, randomized IDs may be generated with |
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141 | <citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s |
142 | <command>new</command> command.</para> | |
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143 | </refsect1> |
144 | ||
145 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
146 | ||
147 | <refsect1> | |
148 | <title>See Also</title> | |
149 | <para> | |
150 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
151 | <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
152 | <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
153 | <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
154 | <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
155 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
156 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
157 | <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
158 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
159 | </para> | |
160 | </refsect1> | |
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161 | |
162 | </refentry> |