typedef size_t (* kblock_read_t) (struct KBlock *b, void *buf, size_t offset, size_t size);
typedef size_t (* kblock_write_t) (struct KBlock *b, const void *buf, size_t offset, size_t size);
typedef int (* kblock_load_t) (struct KBlock *b, block_idx_t index);
typedef int (* kblock_store_t) (struct KBlock *b, block_idx_t index);
typedef size_t (* kblock_read_t) (struct KBlock *b, void *buf, size_t offset, size_t size);
typedef size_t (* kblock_write_t) (struct KBlock *b, const void *buf, size_t offset, size_t size);
typedef int (* kblock_load_t) (struct KBlock *b, block_idx_t index);
typedef int (* kblock_store_t) (struct KBlock *b, block_idx_t index);