sd-id128
systemd
sd-id128
3
sd-id128
sd_id128_t
SD_ID128_MAKE
SD_ID128_MAKE_STR
SD_ID128_NULL
SD_ID128_CONST_STR
SD_ID128_FORMAT_STR
SD_ID128_UUID_FORMAT_STR
SD_ID128_FORMAT_VAL
sd_id128_equal
sd_id128_is_null
APIs for processing 128-bit IDs
#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 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_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_NULL may be used to refer to the 128bit ID consisting of only NUL
bytes.
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() 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("Match for coredumps: %s", 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;
}
SD_ID128_UUID_FORMAT_STR() is similar to
SD_ID128_FORMAT_STR() but includes separating hyphens to conform to the
"canonical representation".
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
systemd-id1281's
new command.
See Also
systemd1,
sd_id128_to_string3,
sd_id128_randomize3,
sd_id128_get_machine3,
printf3,
journalctl1,
sd-journal7,
pkg-config1,
machine-id5