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_MAKE_STR
</refname>
51 <refname>SD_ID128_NULL
</refname>
52 <refname>SD_ID128_CONST_STR
</refname>
53 <refname>SD_ID128_FORMAT_STR
</refname>
54 <refname>SD_ID128_FORMAT_VAL
</refname>
55 <refname>sd_id128_equal
</refname>
56 <refname>sd_id128_is_null
</refname>
57 <refpurpose>APIs for processing
128-bit IDs
</refpurpose>
62 <funcsynopsisinfo>#include
<systemd/sd-id128.h
></funcsynopsisinfo>
66 <command>pkg-config --cflags --libs libsystemd
</command>
72 <title>Description
</title>
74 <para><filename>sd-id128.h
</filename> provides APIs to process and
75 generate
128-bit ID values. The
128-bit ID values processed and
76 generated by these APIs are a generalization of OSF UUIDs as
77 defined by
<ulink url=
"https://tools.ietf.org/html/rfc4122">RFC
78 4122</ulink> but use a simpler string format. These functions
79 impose no structure on the used IDs, much unlike OSF UUIDs or
80 Microsoft GUIDs, but are fully compatible with those types of IDs.
84 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
85 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
87 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
88 for more information about the implemented functions.
</para>
90 <para>A
128-bit ID is implemented as the following
93 <programlisting>typedef union sd_id128 {
96 } sd_id128_t;
</programlisting>
98 <para>This union type allows accessing the
128-bit ID as
16
99 separate bytes or two
64-bit words. It is generally safer to
100 access the ID components by their
8-bit array to avoid endianness
101 issues. This union is intended to be passed call-by-value (as
102 opposed to call-by-reference) and may be directly manipulated by
105 <para>A couple of macros are defined to denote and decode
128-bit
108 <para><function>SD_ID128_MAKE()
</function> may be used to denote a
109 constant
128-bit ID in source code. A commonly used idiom is to
110 assign a name to a
128-bit ID using this macro:
</para>
112 <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>
114 <para><function>SD_ID128_NULL
</function> may be used to refer to the
128bit ID consisting of only NUL
117 <para><function>SD_ID128_MAKE_STR()
</function> is similar to
<function>SD_ID128_MAKE()
</function>, but creates a
118 <type>const char*
</type> expression that can be conveniently used in message formats and such:
</para>
120 <programlisting>#include
<stdio.h
>
121 #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)
123 int main(int argc, char **argv) {
124 puts(
"Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
129 <para><function>SD_ID128_CONST_STR()
</function> may be used to
130 convert constant
128-bit IDs into constant strings for output. The
131 following example code will output the string
132 "fc2e22bc6ee647b6b90729ab34a250b1":
</para>
133 <programlisting>int main(int argc, char *argv[]) {
134 puts(
"Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
137 <para><function>SD_ID128_FORMAT_STR()
</function> and
138 <function>SD_ID128_FORMAT_VAL()
</function> may be used to format a
140 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
141 format string, as shown in the following example:
</para>
143 <programlisting>int main(int argc, char *argv[]) {
145 id = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
146 printf(
"The ID encoded in this C file is " SD_ID128_FORMAT_STR
".\n", SD_ID128_FORMAT_VAL(id));
150 <para>Use
<function>sd_id128_equal()
</function> to compare two
128-bit IDs:
</para>
152 <programlisting>int main(int argc, char *argv[]) {
154 a = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
155 b = SD_ID128_MAKE(f2,
28,
88,
9c,
5f,
09,
44,
15,
9d,d7,
04,
77,
58,cb,e7,
3e);
157 assert(sd_id128_equal(a, c));
158 assert(!sd_id128_equal(a, b));
162 <para>Use
<function>sd_id128_is_null()
</function> to check if an
128bit ID consists of only NUL bytes:
</para>
164 <programlisting>int main(int argc, char *argv[]) {
165 assert(sd_id128_is_null(SD_ID128_NULL));
168 <para>Note that new, randomized IDs may be generated with
169 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
170 <option>--new-id128
</option> option.
</para>
173 <xi:include href=
"libsystemd-pkgconfig.xml" />
176 <title>See Also
</title>
178 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
179 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
180 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
181 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
182 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
183 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
184 <citerefentry><refentrytitle>sd-journal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
185 <citerefentry project='die-net'
><refentrytitle>pkg-config
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
186 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>