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 SPDX-License-Identifier: LGPL-2.1+
8 This file is part of systemd.
10 Copyright 2012 Lennart Poettering
12 systemd is free software; you can redistribute it and/or modify it
13 under the terms of the GNU Lesser General Public License as published by
14 the Free Software Foundation; either version 2.1 of the License, or
15 (at your option) any later version.
17 systemd is distributed in the hope that it will be useful, but
18 WITHOUT ANY WARRANTY; without even the implied warranty of
19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20 Lesser General Public License for more details.
22 You should have received a copy of the GNU Lesser General Public License
23 along with systemd; If not, see <http://www.gnu.org/licenses/>.
26 <refentry id=
"sd-id128"
27 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
30 <title>sd-id128
</title>
31 <productname>systemd
</productname>
35 <contrib>Developer
</contrib>
36 <firstname>Lennart
</firstname>
37 <surname>Poettering
</surname>
38 <email>lennart@poettering.net
</email>
44 <refentrytitle>sd-id128
</refentrytitle>
45 <manvolnum>3</manvolnum>
49 <refname>sd-id128
</refname>
50 <refname>sd_id128_t
</refname>
51 <refname>SD_ID128_MAKE
</refname>
52 <refname>SD_ID128_MAKE_STR
</refname>
53 <refname>SD_ID128_NULL
</refname>
54 <refname>SD_ID128_CONST_STR
</refname>
55 <refname>SD_ID128_FORMAT_STR
</refname>
56 <refname>SD_ID128_FORMAT_VAL
</refname>
57 <refname>sd_id128_equal
</refname>
58 <refname>sd_id128_is_null
</refname>
59 <refpurpose>APIs for processing
128-bit IDs
</refpurpose>
64 <funcsynopsisinfo>#include
<systemd/sd-id128.h
></funcsynopsisinfo>
68 <command>pkg-config --cflags --libs libsystemd
</command>
74 <title>Description
</title>
76 <para><filename>sd-id128.h
</filename> provides APIs to process and
77 generate
128-bit ID values. The
128-bit ID values processed and
78 generated by these APIs are a generalization of OSF UUIDs as
79 defined by
<ulink url=
"https://tools.ietf.org/html/rfc4122">RFC
80 4122</ulink> but use a simpler string format. These functions
81 impose no structure on the used IDs, much unlike OSF UUIDs or
82 Microsoft GUIDs, but are fully compatible with those types of IDs.
86 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
87 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
89 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
90 for more information about the implemented functions.
</para>
92 <para>A
128-bit ID is implemented as the following
95 <programlisting>typedef union sd_id128 {
98 } sd_id128_t;
</programlisting>
100 <para>This union type allows accessing the
128-bit ID as
16
101 separate bytes or two
64-bit words. It is generally safer to
102 access the ID components by their
8-bit array to avoid endianness
103 issues. This union is intended to be passed call-by-value (as
104 opposed to call-by-reference) and may be directly manipulated by
107 <para>A couple of macros are defined to denote and decode
128-bit
110 <para><function>SD_ID128_MAKE()
</function> may be used to denote a
111 constant
128-bit ID in source code. A commonly used idiom is to
112 assign a name to a
128-bit ID using this macro:
</para>
114 <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>
116 <para><function>SD_ID128_NULL
</function> may be used to refer to the
128bit ID consisting of only NUL
119 <para><function>SD_ID128_MAKE_STR()
</function> is similar to
<function>SD_ID128_MAKE()
</function>, but creates a
120 <type>const char*
</type> expression that can be conveniently used in message formats and such:
</para>
122 <programlisting>#include
<stdio.h
>
123 #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)
125 int main(int argc, char **argv) {
126 puts(
"Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
131 <para><function>SD_ID128_CONST_STR()
</function> may be used to
132 convert constant
128-bit IDs into constant strings for output. The
133 following example code will output the string
134 "fc2e22bc6ee647b6b90729ab34a250b1":
</para>
135 <programlisting>int main(int argc, char *argv[]) {
136 puts(
"Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
139 <para><function>SD_ID128_FORMAT_STR()
</function> and
140 <function>SD_ID128_FORMAT_VAL()
</function> may be used to format a
142 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
143 format string, as shown in the following example:
</para>
145 <programlisting>int main(int argc, char *argv[]) {
147 id = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
148 printf(
"The ID encoded in this C file is " SD_ID128_FORMAT_STR
".\n", SD_ID128_FORMAT_VAL(id));
152 <para>Use
<function>sd_id128_equal()
</function> to compare two
128-bit IDs:
</para>
154 <programlisting>int main(int argc, char *argv[]) {
156 a = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
157 b = SD_ID128_MAKE(f2,
28,
88,
9c,
5f,
09,
44,
15,
9d,d7,
04,
77,
58,cb,e7,
3e);
159 assert(sd_id128_equal(a, c));
160 assert(!sd_id128_equal(a, b));
164 <para>Use
<function>sd_id128_is_null()
</function> to check if an
128bit ID consists of only NUL bytes:
</para>
166 <programlisting>int main(int argc, char *argv[]) {
167 assert(sd_id128_is_null(SD_ID128_NULL));
170 <para>Note that new, randomized IDs may be generated with
171 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
172 <option>--new-id128
</option> option.
</para>
175 <xi:include href=
"libsystemd-pkgconfig.xml" />
178 <title>See Also
</title>
180 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
181 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
182 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
183 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
184 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
185 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
186 <citerefentry><refentrytitle>sd-journal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
187 <citerefentry project='die-net'
><refentrytitle>pkg-config
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
188 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>