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 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. systemd1, sd_id128_to_string3, sd_id128_randomize3, sd_id128_get_machine3, printf3, journalctl1, sd-journal7, pkg-config1, machine-id5