Generic key value store interface to store and retrieve key-value entries on different kind of memory devices e.g. RAM, FLASH (nor or nand), EEPROM, ...
KVS stores Key-value entries as:
Entry header: the length of the header is 4 byte.
byte 0: CRC8 over the header
byte 1: key length (this allows keys of up to 256 chars)
byte 2-3: value length bytes
Entry data:
key bytes (key length)
value bytes (value length)
CRC32 over key and value
fill bytes (for alignment)
Entries are written sequentially to blocks that have a configurable size. At the beginning of each block a special entry is written that has the key size set to 0 and its data consists of a wrap counter (4 byte) and a cookie. The wrap counter is increased each time the memory wraps around. The use of the cookie is left up to the user, it could e.g. by used as means to identify the key value store or its version.
When a new block is started the key value store verifies whether it needs to move old entries to keep a copy and does so if required.
The configurable block size needs to be a power of 2. The block size limits the maximum size of an entry as it needs to fit within one block. The block size is not limited to an erase block size of the memory device, this allows using memory devices with non constant erase block sizes. However in this last case careful parameter selection is required to guarantee that there will be no loss of data.
The API for KVS is documented in the header file kvs.h.