systemd Developer Lennart Poettering lennart@poettering.net sd-id128 7 sd-id128 sd_id128_t SD_ID128_MAKE SD_ID128_FORMAT_STR SD_ID128_FORMAT_VAL sd_id128_equal APIs for processing 128 bit IDs #include <systemd/sd-id128.h> pkg-config --cflags --libs libsystemd-id128 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, 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 and sd_id128_randomize3 for more information about the functions implemented. 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 2 64 bit words. It is generally safer to access the ID components by their 8 bit array to avoid endianess 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 write a 128 bit ID in source code. A commonly used idiom is to give 128 bit IDs names 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_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 --new-id command. These APIs are implemented as shared library, which can be compiled and linked to with the libsystemd-id128 pkg-config1 file. systemd1, sd_id128_to_string3, sd_id128_randomize3, printf3, journalctl1, sd-journal7, pkg-config1, machine-id5