mmcblk0p3 is ext2 + journal
mmcblk0p4 is a single partition, FAT-32, hard-disk format (including the MBR and partition table) - it gets mounted for the user with a fuse, loop mount and displacement so only the file storage area shows.
How to make them both "not ready" - 1024 bytes of zero and the Kindle startup scripting will rebuild them.
I am not sure how to make both of them "already ready". Maybe just format them.