[Yaffs] write_oob/ecc implementation necessary?

Hi all,
We are using a flash card with 32 KB page size and hardware generates ecc
for every 512 bytes . There is extra 8 bytes available for storing meta
information for the 512 bytes
It is not possible to directly write on to the spare area. As I understand,
we can ask yaffs to use in-band tags for every 512 bytes.
Is it required for the driver to implement the write_oob or write_ecc
function for mounting yaffs ?.

Of the mtd functions, read, write, erase, write_oob ,read_oob, sync and
mark_block_bad , we have implemented the basic read write and erase. What
other functions are absolutely essential for using yaffs and which can be
stubs?.
Thanks,
mugunthan