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>7</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> and
82 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
83 for more information about the implemented
86 <para>A 128 bit ID is implemented as the following
89 <programlisting>typedef union sd_id128 {
92 } sd_id128_t;</programlisting>
94 <para>This union type allows accessing the 128 bit ID
95 as 16 separate bytes or two 64 bit words. It is generally
96 safer to access the ID components by their 8 bit array
97 to avoid endianness issues. This union is intended to
98 be passed call-by-value (as opposed to
99 call-by-reference) and may be directly manipulated by
102 <para>A couple of macros are defined to denote and
103 decode 128 bit IDs:</para>
105 <para><function>SD_ID128_MAKE()</function> may be used
106 to write a 128 bit ID in source code. A commonly used
107 idiom is to give 128 bit IDs names using this macro:</para>
109 <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>
111 <para><function>SD_ID128_FORMAT_STR</function> and
112 <function>SD_ID128_FORMAT_VAL()</function> may be used
113 to format a 128 bit ID in a
114 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
115 format string, as shown in the following
118 <programlisting>int main(int argc, char *argv[]) {
120 id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
121 printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
125 <para>Use <function>sd_id128_equal()</function> to compare two 128 bit IDs:</para>
127 <programlisting>int main(int argc, char *argv[]) {
129 a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
130 b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
132 assert(sd_id128_equal(a, c));
133 assert(!sd_id128_equal(a, b));
137 <para>Note that new, randomized IDs may be generated
139 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
140 <literal>--new-id</literal> option.</para>
146 <para>These APIs are implemented as a shared library,
147 which can be compiled and linked to with the
148 <literal>libsystemd-id128</literal>
149 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
155 <title>See Also</title>
157 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
158 <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
159 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
160 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
161 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
162 <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
163 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
164 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>