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">
6 This file is part of systemd.
8 Copyright 2012 Lennart Poettering
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.
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.
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/>.
24 <refentry id="sd-id128"
25 xmlns:xi="http://www.w3.org/2001/XInclude">
28 <title>sd-id128</title>
29 <productname>systemd</productname>
33 <contrib>Developer</contrib>
34 <firstname>Lennart</firstname>
35 <surname>Poettering</surname>
36 <email>lennart@poettering.net</email>
42 <refentrytitle>sd-id128</refentrytitle>
43 <manvolnum>3</manvolnum>
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>
59 <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
63 <command>pkg-config --cflags --libs libsystemd</command>
69 <title>Description</title>
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.
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
89 <para>A 128-bit ID is implemented as the following
92 <programlisting>typedef union sd_id128 {
95 } sd_id128_t;</programlisting>
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
105 <para>A couple of macros are defined to denote and
106 decode 128-bit IDs:</para>
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>
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>
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
119 "fc2e22bc6ee647b6b90729ab34a250b1":</para>
120 <programlisting>int main(int argc, char *argv[]) {
121 puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
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
131 <programlisting>int main(int argc, char *argv[]) {
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));
138 <para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para>
140 <programlisting>int main(int argc, char *argv[]) {
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);
145 assert(sd_id128_equal(a, c));
146 assert(!sd_id128_equal(a, b));
150 <para>Note that new, randomized IDs may be generated
152 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
153 <option>--new-id</option> option.</para>
156 <xi:include href="libsystemd-pkgconfig.xml" />
159 <title>See Also</title>
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>