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/*
* Copyright (C) 2017 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @defgroup sys_luid Locally Unique ID Generator
* @ingroup sys
* @brief Generate system wide (locally) unique IDs
*
* This module generates system wide, variable length unique IDs based on on the
* cpuid module. If the cpuid module is not present, the module falls back to a
* pre-defined, constant seed for creating unique IDs.
*
* The main purpose of this module is to have a unified way for e.g. creating
* hardware addresses and similar.
*
* The IDs generated by this module are base created from a constant base part
* and a dynamic portion, which is XORed into the base ID. If the cpuid module
* is present, the base ID is created from the CPU's unique ID. If not, the
* base ID is created by simple 'memsetting' the base ID with the defined
* backup seed value.
*
* Once the base ID is generated, a LUID is generated by (i) XORing a counter
* value with the LSB of the base ID, or (ii) by XORing the least significant
* byes with a value given by the user.
*
* Example: Calling `luid_base(&buf, 8)` will always yield an identical value,
* independent how often the function is called. But calling
* `luid_base(&buf, 2)` afterwards will results in a different value, if the
* cpuid module is present, and in the same (but shorter) value if not.
*
* Example: Calling `luid_get(&buf, 8)` four times in a row, will yield four
* different IDs, differing in their LSB.
*
* Example: Calling `luid_custom(&buf, 8, 123)` will always yield the same
* value, but calling `luid_custom(&buf, 8, 124)` will differ.
*
* @note This module generates locally unique IDs without any guarantees
* on their structure. These LUIDs are not compatible nor conform
* to UUIDs as defined in RFC4122.
*
* @{
* @file
* @brief Header of the unique ID generation module
*
* @author Hauke Petersen <hauke.petersen@fu-berlin.de>
*/
#ifndef LUID_H
#define LUID_H
#include <stddef.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Value used as based for the LUIDs in case the cpuid module is not
* present
*/
#ifndef LUID_BACKUP_SEED
#define LUID_BACKUP_SEED 0x23
#endif
/**
* @brief Get a unique ID
*
* The resulting ID is built from the base ID generated with luid_base(), which
* isXORed with an 8-bit incrementing counter value into the most significant
* byte.
*
* @note The resulting LUID will repeat after 255 calls.
*
* @param[out] buf memory location to copy the LUID into. MUST be able to
* hold at least @p len bytes
* @param[in] len length of the LUID in bytes
*/
void luid_get(void *buf, size_t len);
/**
* @brief Get a custom unique ID based on a user given generator value
*
* The resulting ID is built from the base ID XORed with @p gen in the base
* ID's most significant bytes.
*
* @note Calling this function with identical values for @p gen and @p len
* will always result in identical LUIDs.
*
* @param[out] buf memory location to copy the LUID into. MUST be able to
* hold at least @p len bytes
* @param[in] len length of the LUID in bytes
* @param[in] gen custom LUID generator value
*/
void luid_custom(void *buf, size_t len, int gen);
/**
* @brief Get a LUID base value
*
* The luid module creates the value dependent on the given @p len value using
* the cpuid module if present or a static seed value (@ref LUID_BACKUP_SEED) if
* not.
*
* @param[out] buf memory location to copy the LUID into. MUST be able to
* hold at least @p len bytes
* @param[in] len length of the LUID in bytes
*/
void luid_base(void *buf, size_t len);
#ifdef __cplusplus
}
#endif
#endif /* LUID_H */
/** @} */