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NAME | SYNOPSIS | DESCRIPTION | NOTES | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD-ID128(3) sd-id128 SD-ID128(3)
sd-id128, SD_ID128_ALLF, SD_ID128_CONST_STR, SD_ID128_FORMAT_STR,
SD_ID128_FORMAT_VAL, SD_ID128_MAKE, SD_ID128_MAKE_STR,
SD_ID128_MAKE_UUID_STR, SD_ID128_NULL, SD_ID128_UUID_FORMAT_STR,
sd_id128_equal, sd_id128_string_equal, sd_id128_in_set,
sd_id128_in_set_sentinel, sd_id128_in_setv, sd_id128_is_allf,
sd_id128_is_null, sd_id128_t - APIs for processing 128-bit IDs
#include <systemd/sd-id128.h>
SD_ID128_ALLF
SD_ID128_NULL
SD_ID128_CONST_STR(id)
SD_ID128_FORMAT_STR
SD_ID128_FORMAT_VAL(id)
SD_ID128_MAKE(v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, vA, vB, vC,
vD, vE, vF)
SD_ID128_MAKE_STR(v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, vA, vB,
vC, vD, vE, vF)
SD_ID128_MAKE_UUID_STR(v0, v1, v2, v3, v4, v5, v6, v7, v8, v9,
vA, vB, vC, vD, vE, vF)
SD_ID128_UUID_FORMAT_STR
int sd_id128_equal(sd_id128_t a, sd_id128_t b);
int sd_id128_string_equal(const char *a, sd_id128_t b);
int sd_id128_is_null(sd_id128_t id);
int sd_id128_is_allf(sd_id128_t id);
int sd_id128_in_setv(sd_id128_t id, va_list ap);
int sd_id128_in_set_sentinel(sd_id128_t id, ..., SD_ID128_NULL);
int sd_id128_in_set(sd_id128_t id, ...);
pkg-config --cflags --libs libsystemd
sd-id128.h is part of libsystemd(3) and provides APIs to
generate, convert, and compare 128-bit ID values. The 128-bit ID
values processed and generated by these APIs are a generalization
of OSF UUIDs as defined by RFC 4122[1] but use a simpler string
format. These functions impose no structure on the used IDs, much
unlike OSF UUIDs or Microsoft GUIDs, but are mostly compatible
with those types of IDs.
A 128-bit ID is implemented as the following union type:
typedef union sd_id128 {
uint8_t bytes[16];
uint64_t qwords[2];
} sd_id128_t;
This union type allows accessing the 128-bit ID as 16 separate
bytes or two 64-bit words. It is generally safer to access the ID
components by their 8-bit array to avoid endianness issues. This
union is intended to be passed by value (as opposed to
pass-by-reference) and may be directly manipulated by clients.
A couple of macros are defined to denote and decode 128-bit IDs:
SD_ID128_MAKE() is used to write a constant ID in source code. A
commonly used idiom is to assign a name to an ID using this
macro:
#define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)
SD_ID128_NULL defines an ID consisting of only NUL bytes (i.e.
all bits off).
SD_ID128_ALLF defines an ID consisting of only 0xFF bytes (i.e.
all bits on).
SD_ID128_MAKE_STR() is similar to SD_ID128_MAKE(), but creates a
const char* expression that can be conveniently used in message
formats and such:
#include <stdio.h>
#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)
int main(int argc, char **argv) {
puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
}
SD_ID128_CONST_STR() converts constant IDs into constant strings
for output. The following example code will output the string
"fc2e22bc6ee647b6b90729ab34a250b1":
int main(int argc, char *argv[]) {
puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
}
SD_ID128_FORMAT_STR and SD_ID128_FORMAT_VAL() is used to format
an ID in a printf(3) format string, as shown in the following
example:
int main(int argc, char *argv[]) {
sd_id128_t id;
id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
return 0;
}
SD_ID128_UUID_FORMAT_STR and SD_ID128_MAKE_UUID_STR() are similar
to SD_ID128_FORMAT_STR and SD_ID128_MAKE_STR(), but include
separating hyphens to conform to the "UUID canonical
representation[2]". They format the string based on RFC4122[1]
Variant 1 rules, i.e. converting from Big Endian byte order. This
matches behaviour of most other Linux userspace infrastructure.
It's probably best to avoid UUIDs of other variants, in order to
avoid unnecessary ambiguities. All 128-bit IDs generated by the
sd-id128 APIs strictly conform to Variant 1 Version 4 UUIDs, as
per RFC 4122.
sd_id128_equal() compares two 128-bit IDs:
int main(int argc, char *argv[]) {
sd_id128_t a, b, c;
a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
c = a;
assert(sd_id128_equal(a, c));
assert(!sd_id128_equal(a, b));
return 0;
}
sd_id128_string_equal() is similar to sd_id128_equal(), but the
first ID is formatted as const char*. The same restrictions apply
as to the first argument of sd_id128_from_string().
sd_id128_is_null() checks if an ID consists of only NUL bytes:
assert(sd_id128_is_null(SD_ID128_NULL));
Similarly, sd_id128_is_allf() checks if an ID consists of only
0xFF bytes (all bits on):
assert(sd_id128_is_allf(SD_ID128_ALLF));
sd_id128_in_set_sentinel() takes a list of IDs and returns true
if the first argument is equal to any of the subsequent
arguments. The argument list is terminated by an SD_ID128_NULL
sentinel, which must be present.
sd_id128_in_set() is a convenience function that takes a list of
IDs and returns true if the first argument is equal to any of the
subsequent arguments:
int main(int argc, char *argv[]) {
sd_id12_t a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
assert(sd_id128_in_set(a, a));
assert(sd_id128_in_set(a, a, a));
assert(!sd_id128_in_set(a));
assert(!sd_id128_in_set(a,
SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e)
SD_ID128_MAKE(2f,88,28,5f,9c,44,09,9d,d7,15,77,04,bc,85,7e,e3)
SD_ID128_ALLF));
return 0;
}
sd_id128_in_set() is defined as a macro over
sd_id128_in_set_sentinel(), adding the SD_ID128_NULL sentinel
automatically. Since sd_id128_in_set_sentinel() uses
SD_ID128_NULL as the sentinel, SD_ID128_NULL cannot be otherwise
placed in the argument list.
sd_id128_in_setv() is similar to sd_id128_in_set_sentinel(), but
takes a struct varargs argument.
New randomized IDs may be generated with systemd-id128(1)'s new
command.
See sd_id128_to_string(3), sd_id128_randomize(3) and
sd_id128_get_machine(3) for information about other implemented
functions.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
sd_id128_equal(), sd_id128_string_equal(), sd_id128_is_null(),
sd_id128_is_allf(), sd_id128_in_setv(),
sd_id128_in_set_sentinel(), and sd_id128_in_set() were added in
version 252.
systemd(1), sd_id128_to_string(3), sd_id128_randomize(3),
sd_id128_get_machine(3), printf(3), journalctl(1), sd-journal(7),
pkg-config(1), machine-id(5)
1. RFC 4122
https://tools.ietf.org/html/rfc4122
2. UUID canonical representation
https://en.wikipedia.org/wiki/Universally_unique_identifier#Format
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SD-ID128(3)
Pages that refer to this page: systemd-id128(1), libsystemd(3), sd_id128_get_machine(3), sd_id128_randomize(3), sd_id128_to_string(3), sd-journal(3), machine-id(5), systemd.network(5), systemd.directives(7), systemd.index(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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