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">
27 <title>sd-id128</title>
28 <productname>systemd</productname>
32 <contrib>Developer</contrib>
33 <firstname>Lennart</firstname>
34 <surname>Poettering</surname>
35 <email>lennart@poettering.net</email>
41 <refentrytitle>sd-id128</refentrytitle>
42 <manvolnum>3</manvolnum>
46 <refname>sd-id128</refname>
47 <refname>sd_id128_t</refname>
48 <refname>SD_ID128_MAKE</refname>
49 <refname>SD_ID128_FORMAT_STR</refname>
50 <refname>SD_ID128_FORMAT_VAL</refname>
51 <refname>sd_id128_equal</refname>
52 <refpurpose>APIs for processing 128 bit IDs</refpurpose>
57 <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
61 <command>pkg-config --cflags --libs libsystemd-id128</command>
67 <title>Description</title>
69 <para><filename>sd-id128.h</filename> provides APIs to
70 process and generate 128 bit ID values. The 128 bit ID
71 values processed and generated by these APIs are a
72 generalization of OSF UUIDs as defined by <ulink
73 url="http://tools.ietf.org/html/rfc4122">RFC
74 4122</ulink>, though use a simpler string
75 formatting. These functions impose no structure on the
76 used IDs, much unlike OSF UUIDs or Microsoft GUIDs,
77 but are fully compatible with those types of IDs.
81 <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
82 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
83 <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
84 for more information about the implemented
87 <para>A 128 bit ID is implemented as the following
90 <programlisting>typedef union sd_id128 {
93 } sd_id128_t;</programlisting>
95 <para>This union type allows accessing the 128 bit ID
96 as 16 separate bytes or two 64 bit words. It is generally
97 safer to access the ID components by their 8 bit array
98 to avoid endianness issues. This union is intended to
99 be passed call-by-value (as opposed to
100 call-by-reference) and may be directly manipulated by
103 <para>A couple of macros are defined to denote and
104 decode 128 bit IDs:</para>
106 <para><function>SD_ID128_MAKE()</function> may be used
107 to write a 128 bit ID in source code. A commonly used
108 idiom is to give 128 bit IDs names using this macro:</para>
110 <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>
112 <para><function>SD_ID128_FORMAT_STR</function> and
113 <function>SD_ID128_FORMAT_VAL()</function> may be used
114 to format a 128 bit ID in a
115 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
116 format string, as shown in the following
119 <programlisting>int main(int argc, char *argv[]) {
121 id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
122 printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
126 <para>Use <function>sd_id128_equal()</function> to compare two 128 bit IDs:</para>
128 <programlisting>int main(int argc, char *argv[]) {
130 a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
131 b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
133 assert(sd_id128_equal(a, c));
134 assert(!sd_id128_equal(a, b));
138 <para>Note that new, randomized IDs may be generated
140 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
141 <literal>--new-id</literal> option.</para>
147 <para>These APIs are implemented as a shared library,
148 which can be compiled and linked to with the
149 <literal>libsystemd-id128</literal>
150 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
156 <title>See Also</title>
158 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
159 <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
160 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
161 <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
162 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
163 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
164 <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
165 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
166 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>