how to build ext2 rootfs in EP2C35 (dev kit)

I would like to use a ext2 fs instead of a romfs for my rootfs

I tried genext2fs, but it doesn't work. (pb with device file ??).

When I boot , I have the followin message :

"Freeing unused kernel memory: 60k freed (0x413c000 - 0x414a000)

EXT2-fs error (device mtdblock0): ext2_check_page: bad entry in directory# 2: re

c_len is smaller than minimal - offset=0, inode=0, rec_len=0, name_len=0"

Thanks

Laurent

PS : My board is the NIOSII EP2C35( altera DEV KIT ) .

I tried jffs2 fs ( with mkfs.jffs2) and it doesn't work.