sd-id128
systemd
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_NULL
SD_ID128_UUID_FORMAT_STR
sd_id128_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>
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 128-bit 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 128-bit ID consists of only
NUL bytes:
assert(sd_id128_is_null(SD_ID128_NULL));
Similarly, use sd_id128_is_allf() to check if an 128-bit ID consists of only
0xFF bytes (all bits on):
assert(sd_id128_is_allf(SD_ID128_ALLF));
For convenience, sd_id128_in_set() takes a list of IDs and
returns true if any are equal to the first argument:
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. 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.
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