mtdMTD device structure
fsbufbuffer given by fs driver
oobselout of band selection structre
autoplace1 = place given buffer into the oob bytes
numpagesnumber of pages to prepare
1. Filesystem buffer available and autoplacement is off, return filesystem buffer 2. No filesystem buffer or autoplace is off, return internal buffer 3. Filesystem buffer is given and autoplace selected put data from fs buffer into internal buffer and retrun internal buffer