1SD-ID128(3) sd-id128 SD-ID128(3)
2
6 sd-id128, SD_ID128_ALLF, SD_ID128_CONST_STR, SD_ID128_FORMAT_STR,
7 SD_ID128_FORMAT_VAL, SD_ID128_MAKE, SD_ID128_MAKE_STR,
8 SD_ID128_MAKE_UUID_STR, SD_ID128_NULL, SD_ID128_UUID_FORMAT_STR,
9 sd_id128_equal, sd_id128_in_set, sd_id128_in_set_sentinel,
10 sd_id128_in_setv, sd_id128_is_allf, sd_id128_is_null, sd_id128_t - APIs
11 for processing 128-bit IDs
12
14 #include <systemd/sd-id128.h>
15 pkg-config --cflags --libs libsystemd
17
19 sd-id128.h provides APIs to process and generate 128-bit ID values. The
20 128-bit ID values processed and generated by these APIs are a
21 generalization of OSF UUIDs as defined by RFC 4122[1] but use a simpler
22 string format. These functions impose no structure on the used IDs,
23 much unlike OSF UUIDs or Microsoft GUIDs, but are mostly compatible
24 with those types of IDs.
25 See sd_id128_to_string(3), sd_id128_randomize(3) and
27 sd_id128_get_machine(3) for more information about the implemented
28 functions.
29 A 128-bit ID is implemented as the following union type:
31 typedef union sd_id128 {
33 uint8_t bytes[16];
34 uint64_t qwords[2];
35 } sd_id128_t;
36 This union type allows accessing the 128-bit ID as 16 separate bytes or
38 two 64-bit words. It is generally safer to access the ID components by
39 their 8-bit array to avoid endianness issues. This union is intended to
40 be passed call-by-value (as opposed to call-by-reference) and may be
41 directly manipulated by clients.
42 A couple of macros are defined to denote and decode 128-bit IDs:
44 SD_ID128_MAKE() may be used to denote a constant 128-bit ID in source
46 code. A commonly used idiom is to assign a name to a 128-bit ID using
47 this macro:
48 #define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)
50 SD_ID128_NULL may be used to refer to the 128-bit ID consisting of only
52 NUL bytes (i.e. all bits off).
53 SD_ID128_ALLF may be used to refer to the 128-bit ID consisting of only
55 0xFF bytes (i.e. all bits on).
56 SD_ID128_MAKE_STR() is similar to SD_ID128_MAKE(), but creates a const
58 char* expression that can be conveniently used in message formats and
59 such:
60 #include <stdio.h>
62 #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)
63 int main(int argc, char **argv) {
65 puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
66 }
67 SD_ID128_CONST_STR() may be used to convert constant 128-bit IDs into
69 constant strings for output. The following example code will output the
70 string "fc2e22bc6ee647b6b90729ab34a250b1":
71 int main(int argc, char *argv[]) {
73 puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
74 }
75 SD_ID128_FORMAT_STR and SD_ID128_FORMAT_VAL() may be used to format a
77 128-bit ID in a printf(3) format string, as shown in the following
78 example:
79 int main(int argc, char *argv[]) {
81 sd_id128_t id;
82 id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
83 printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
84 return 0;
85 }
86 SD_ID128_UUID_FORMAT_STR and SD_ID128_MAKE_UUID_STR() are similar to
88 SD_ID128_FORMAT_STR and SD_ID128_MAKE_STR(), but include separating
89 hyphens to conform to the "canonical representation[2]". They format
90 the string based on RFC4122[1] Variant 1 rules, i.e. converting from
91 Big Endian byte order. This matches behaviour of most other Linux
92 userspace infrastructure. It's probably best to avoid UUIDs of other
93 variants, in order to avoid unnecessary ambiguities. All 128-bit IDs
94 generated by the sd-id128 APIs strictly conform to Variant 1 Version 4
95 UUIDs, as per RFC 4122.
96 Use sd_id128_equal() to compare two 128-bit IDs:
98 int main(int argc, char *argv[]) {
100 sd_id128_t a, b, c;
101 a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
102 b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
103 c = a;
104 assert(sd_id128_equal(a, c));
105 assert(!sd_id128_equal(a, b));
106 return 0;
107 }
108 Use sd_id128_is_null() to check if an 128-bit ID consists of only NUL
110 bytes:
111 assert(sd_id128_is_null(SD_ID128_NULL));
113 Similarly, use sd_id128_is_allf() to check if an 128-bit ID consists of
115 only 0xFF bytes (all bits on):
116 assert(sd_id128_is_allf(SD_ID128_ALLF));
118 For convenience, sd_id128_in_set() takes a list of IDs and returns true
120 if any are equal to the first argument:
121 int main(int argc, char *argv[]) {
123 sd_id12_t a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
124 assert(sd_id128_in_set(a, a));
125 assert(sd_id128_in_set(a, a, a));
126 assert(!sd_id128_in_set(a));
127 assert(!sd_id128_in_set(a,
128 SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e)
129 SD_ID128_MAKE(2f,88,28,5f,9c,44,09,9d,d7,15,77,04,bc,85,7e,e3)
130 SD_ID128_ALLF));
131 return 0;
132 }
133 sd_id128_in_set() is defined as a macro over
135 sd_id128_in_set_sentinel(), adding the SD_ID128_NULL sentinel. Since
136 sd_id128_in_set_sentinel() uses SD_ID128_NULL as the sentinel,
137 SD_ID128_NULL cannot be otherwise placed in the argument list.
138 sd_id128_in_setv() is similar to sd_id128_in_set_sentinel(), but takes
140 a struct varargs argument.
141 Note that new, randomized IDs may be generated with systemd-id128(1)'s
143 new command.
144
146 These APIs are implemented as a shared library, which can be compiled
147 and linked to with the libsystemd pkg-config(1) file.
148
150 systemd(1), sd_id128_to_string(3), sd_id128_randomize(3),
151 sd_id128_get_machine(3), printf(3), journalctl(1), sd-journal(7), pkg-
152 config(1), machine-id(5)
153
155 1. RFC 4122
156 https://tools.ietf.org/html/rfc4122
157 2. canonical representation
159 https://en.wikipedia.org/wiki/Universally_unique_identifier#Format
160systemd 250 SD-ID128(3)