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NAME | SYNOPSIS | DESCRIPTION | NOTES | SEE ALSO | NOTES | COLOPHON |
SD-ID128(3) sd-id128 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_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
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_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 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-id128 option.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
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)
1. RFC 4122
https://tools.ietf.org/html/rfc4122
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
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⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
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systemd 234 SD-ID128(3)
Pages that refer to this page: sd_id128_get_machine(3), sd_id128_randomize(3), sd_id128_to_string(3), sd-journal(3), machine-id(5), systemd.directives(7), systemd.index(7)