1 <?xml version='
1.0'
?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
6 <refentry id=
"sd-id128"
7 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
10 <title>sd-id128
</title>
11 <productname>systemd
</productname>
15 <refentrytitle>sd-id128
</refentrytitle>
16 <manvolnum>3</manvolnum>
20 <refname>sd-id128
</refname>
21 <refname>sd_id128_t
</refname>
22 <refname>SD_ID128_MAKE
</refname>
23 <refname>SD_ID128_MAKE_STR
</refname>
24 <refname>SD_ID128_NULL
</refname>
25 <refname>SD_ID128_CONST_STR
</refname>
26 <refname>SD_ID128_FORMAT_STR
</refname>
27 <refname>SD_ID128_FORMAT_VAL
</refname>
28 <refname>sd_id128_equal
</refname>
29 <refname>sd_id128_is_null
</refname>
30 <refpurpose>APIs for processing
128-bit IDs
</refpurpose>
35 <funcsynopsisinfo>#include
<systemd/sd-id128.h
></funcsynopsisinfo>
39 <command>pkg-config --cflags --libs libsystemd
</command>
45 <title>Description
</title>
47 <para><filename>sd-id128.h
</filename> provides APIs to process and
48 generate
128-bit ID values. The
128-bit ID values processed and
49 generated by these APIs are a generalization of OSF UUIDs as
50 defined by
<ulink url=
"https://tools.ietf.org/html/rfc4122">RFC
51 4122</ulink> but use a simpler string format. These functions
52 impose no structure on the used IDs, much unlike OSF UUIDs or
53 Microsoft GUIDs, but are fully compatible with those types of IDs.
57 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
58 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
60 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
61 for more information about the implemented functions.
</para>
63 <para>A
128-bit ID is implemented as the following
66 <programlisting>typedef union sd_id128 {
69 } sd_id128_t;
</programlisting>
71 <para>This union type allows accessing the
128-bit ID as
16
72 separate bytes or two
64-bit words. It is generally safer to
73 access the ID components by their
8-bit array to avoid endianness
74 issues. This union is intended to be passed call-by-value (as
75 opposed to call-by-reference) and may be directly manipulated by
78 <para>A couple of macros are defined to denote and decode
128-bit
81 <para><function>SD_ID128_MAKE()
</function> may be used to denote a
82 constant
128-bit ID in source code. A commonly used idiom is to
83 assign a name to a
128-bit ID using this macro:
</para>
85 <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>
87 <para><function>SD_ID128_NULL
</function> may be used to refer to the
128bit ID consisting of only NUL
90 <para><function>SD_ID128_MAKE_STR()
</function> is similar to
<function>SD_ID128_MAKE()
</function>, but creates a
91 <type>const char*
</type> expression that can be conveniently used in message formats and such:
</para>
93 <programlisting>#include
<stdio.h
>
94 #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)
96 int main(int argc, char **argv) {
97 puts(
"Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
101 <para><function>SD_ID128_CONST_STR()
</function> may be used to
102 convert constant
128-bit IDs into constant strings for output. The
103 following example code will output the string
104 "fc2e22bc6ee647b6b90729ab34a250b1":
</para>
105 <programlisting>int main(int argc, char *argv[]) {
106 puts(
"Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
109 <para><function>SD_ID128_FORMAT_STR()
</function> and
110 <function>SD_ID128_FORMAT_VAL()
</function> may be used to format a
112 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
113 format string, as shown in the following example:
</para>
115 <programlisting>int main(int argc, char *argv[]) {
117 id = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
118 printf(
"The ID encoded in this C file is " SD_ID128_FORMAT_STR
".\n", SD_ID128_FORMAT_VAL(id));
122 <para>Use
<function>sd_id128_equal()
</function> to compare two
128-bit IDs:
</para>
124 <programlisting>int main(int argc, char *argv[]) {
126 a = SD_ID128_MAKE(ee,
89,be,
71,bd,
6e,
43,d6,
91,e6,c5,
5d,eb,
03,
02,
07);
127 b = SD_ID128_MAKE(f2,
28,
88,
9c,
5f,
09,
44,
15,
9d,d7,
04,
77,
58,cb,e7,
3e);
129 assert(sd_id128_equal(a, c));
130 assert(!sd_id128_equal(a, b));
134 <para>Use
<function>sd_id128_is_null()
</function> to check if an
128bit ID consists of only NUL bytes:
</para>
136 <programlisting>int main(int argc, char *argv[]) {
137 assert(sd_id128_is_null(SD_ID128_NULL));
140 <para>Note that new, randomized IDs may be generated with
141 <citerefentry><refentrytitle>systemd-id128
</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
142 <command>new
</command> command.
</para>
145 <xi:include href=
"libsystemd-pkgconfig.xml" />
148 <title>See Also
</title>
150 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
151 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
152 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
153 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
154 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
155 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
156 <citerefentry><refentrytitle>sd-journal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
157 <citerefentry project='die-net'
><refentrytitle>pkg-config
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
158 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>