This patch should resolve the bugs reported by the sparse tool.
Initial reports were written by "kbuild test robot" managed by fengguang.wu.

In my local machines, I've tested also by running:
> make C=2 CF="-D__CHECK_ENDIAN__"

Accordingly, I've found lots of warnings and bugs related to the endian
conversion. And I've fixed all at this moment.
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

This adds a header file describing the on-disk layout of f2fs.
Signed-off-by: NChangman Lee <cm224.lee@samsung.com>
Signed-off-by: NChul Lee <chur.lee@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>