sd-id128(3)
NAME
sd-id128, sd_id128_t, SD_ID128_MAKE, SD_ID128_NULL, SD_ID128_CONST_STR, SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL, sd_id128_equal, sd_id128_is_null - APIs for processing 128-bit IDs
SYNOPSIS
#include <systemd/sd-id128.h> pkg-config --cflags --libs libsystemd
DESCRIPTION
sd-id128.h provides APIs to process and generate 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 fully compatible with
those types of IDs.
See sd_id128_to_string(3), sd_id128_randomize(3) and
sd_id128_get_machine(3) for more information about the implemented
functions.
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 call-by-value (as opposed to call-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() may be used to denote a constant 128-bit ID in source
code. A commonly used idiom is to assign a name to a 128-bit 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 may be used to refer to the 128bit ID consisting of only
NUL bytes.
SD_ID128_CONST_STR() may be used to convert constant 128-bit IDs into
constant strings for output. The following example code will output the
string "fc2e22bc6ee647b6b90729ab34a250b1":
int main(int argc, char *argv[]) {
puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
}
SD_ID128_FORMAT_STR() and SD_ID128_FORMAT_VAL() may be used to format a
128-bit 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;
}
Use sd_id128_equal() to compare 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;
}
Use sd_id128_is_null() to check if an 128bit ID consists of only NUL
bytes:
int main(int argc, char *argv[]) {
assert(sd_id128_is_null(SD_ID128_NULL));
}
Note that new, randomized IDs may be generated with journalctl(1)'s
--new-id option.
NOTES
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
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
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