sd-id128systemdDeveloperLennartPoetteringlennart@poettering.netsd-id1283sd-id128sd_id128_tSD_ID128_MAKESD_ID128_CONST_STRSD_ID128_FORMAT_STRSD_ID128_FORMAT_VALsd_id128_equalAPIs for processing 128 bit IDs#include <systemd/sd-id128.h>pkg-config --cflags --libs libsystemd-id128Descriptionsd-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, though use a simpler string
formatting. 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_string3,
sd_id128_randomize3 and
sd_id128_get_machine3
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_CONST_STR() may be
used to convert constant 128bit 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
printf3
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;
}Note that new, randomized IDs may be generated
with
journalctl1's
option.NotesThese APIs are implemented as a shared library,
which can be compiled and linked to with the
libsystemd-id128pkg-config1
file.See Alsosystemd1,
sd_id128_to_string3,
sd_id128_randomize3,
sd_id128_get_machine3,
printf3,
journalctl1,
sd-journal7,
pkg-config1,
machine-id5