x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD-ID128(3) sd-id128 SD-ID128(3)
NAME
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
SYNOPSIS
#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
DESCRIPTION
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 "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.
NOTES
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.
SEE ALSO
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)
NOTES
1. RFC 4122
https://tools.ietf.org/html/rfc4122
2. canonical representation
https://en.wikipedia.org/wiki/Universally_unique_identifier#Format
systemd 254 SD-ID128(3)
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