#define UPDATE_MAGIC	"update\0"
#define UPDATE_VERSION	0

struct update_superblock {
	char magic[8];
	uint8_t version;
	uint8_t block_bits;
	uint16_t pad1;
	__le32 chunk_blocks;
	char compression[16];
	__le64 dir_offset;
	__le64 dir_compressed_size;
	__le64 dir_n;
	__le64 pad2;
};

struct update_entry {
	__le32 dest_lo;
	__le16 dest_hi;
	__le16 src_hi;
	__le32 src_lo;
	__le32 offset;
};