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+
9 <refentry id=
"sd-id128"
10 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
13 <title>sd-id128
</title>
14 <productname>systemd
</productname>
18 <refentrytitle>sd-id128
</refentrytitle>
19 <manvolnum>3</manvolnum>
23 <refname>sd-id128
</refname>
24 <refname>sd_id128_t
</refname>
25 <refname>SD_ID128_MAKE
</refname>
26 <refname>SD_ID128_MAKE_STR
</refname>
27 <refname>SD_ID128_NULL
</refname>
28 <refname>SD_ID128_CONST_STR
</refname>
29 <refname>SD_ID128_FORMAT_STR
</refname>
30 <refname>SD_ID128_FORMAT_VAL
</refname>
31 <refname>sd_id128_equal
</refname>
32 <refname>sd_id128_is_null
</refname>
33 <refpurpose>APIs for processing
128-bit IDs
</refpurpose>
38 <funcsynopsisinfo>#include
<systemd/sd-id128.h
></funcsynopsisinfo>
42 <command>pkg-config --cflags --libs libsystemd
</command>
48 <title>Description
</title>
50 <para><filename>sd-id128.h
</filename> provides APIs to process and
51 generate
128-bit ID values. The
128-bit ID values processed and
52 generated by these APIs are a generalization of OSF UUIDs as
53 defined by
<ulink url=
"https://tools.ietf.org/html/rfc4122">RFC
54 4122</ulink> but use a simpler string format. These functions
55 impose no structure on the used IDs, much unlike OSF UUIDs or
56 Microsoft GUIDs, but are fully compatible with those types of IDs.
60 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
61 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
63 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
64 for more information about the implemented functions.
</para>
66 <para>A
128-bit ID is implemented as the following
69 <programlisting>typedef union sd_id128 {
72 } sd_id128_t;
</programlisting>
74 <para>This union type allows accessing the
128-bit ID as
16
75 separate bytes or two
64-bit words. It is generally safer to
76 access the ID components by their
8-bit array to avoid endianness
77 issues. This union is intended to be passed call-by-value (as
78 opposed to call-by-reference) and may be directly manipulated by
81 <para>A couple of macros are defined to denote and decode
128-bit
84 <para><function>SD_ID128_MAKE()
</function> may be used to denote a
85 constant
128-bit ID in source code. A commonly used idiom is to
86 assign a name to a
128-bit ID using this macro:
</para>
88 <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>
90 <para><function>SD_ID128_NULL
</function> may be used to refer to the
128bit ID consisting of only NUL
93 <para><function>SD_ID128_MAKE_STR()
</function> is similar to
<function>SD_ID128_MAKE()
</function>, but creates a
94 <type>const char*
</type> expression that can be conveniently used in message formats and such:
</para>
96 <programlisting>#include
<stdio.h
>
97 #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)
99 int main(int argc, char **argv) {
100 puts(
"Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
104 <para><function>SD_ID128_CONST_STR()
</function> may be used to
105 convert constant
128-bit IDs into constant strings for output. The
106 following example code will output the string
107 "fc2e22bc6ee647b6b90729ab34a250b1":
</para>
108 <programlisting>int main(int argc, char *argv[]) {
109 puts(
"Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
112 <para><function>SD_ID128_FORMAT_STR()
</function> and
113 <function>SD_ID128_FORMAT_VAL()
</function> may be used to format a
115 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
116 format string, as shown in the following example:
</para>
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>Use
<function>sd_id128_is_null()
</function> to check if an
128bit ID consists of only NUL bytes:
</para>
139 <programlisting>int main(int argc, char *argv[]) {
140 assert(sd_id128_is_null(SD_ID128_NULL));
143 <para>Note that new, randomized IDs may be generated with
144 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
145 <option>--new-id128
</option> option.
</para>
148 <xi:include href=
"libsystemd-pkgconfig.xml" />
151 <title>See Also
</title>
153 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
154 <citerefentry><refentrytitle>sd_id128_to_string
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
155 <citerefentry><refentrytitle>sd_id128_randomize
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
156 <citerefentry><refentrytitle>sd_id128_get_machine
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
157 <citerefentry project='man-pages'
><refentrytitle>printf
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
158 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
159 <citerefentry><refentrytitle>sd-journal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
160 <citerefentry project='die-net'
><refentrytitle>pkg-config
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
161 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>