[Yaffs] Some confuse with yaffs2 image

I have tested yaffs2 with nandsim, and have some troubles.
Here they are:

# modprobe nandsim second_id_byte=0xaa fourth_id_byte=0x15
# modprbe mtdblock
# modprobe yaffs2
# mknod /dev/mtd0 c 90 0
# flash_eraseall /dev/mtd0
# mkyaffs2image rootfs/ yaffs2.img
# nandwrite -p /dev/mtd0 yaffs2.img
# mount -t yaffs2 /dev/mtdblock0 /mnt/
# ls -l /mnt/
lost+found


But if i test with jffs2, it has difirence:

# modprobe jffs2
# flash_eraseall /dev/mtd0
# mkfs.jffs2 -d rootfs -s 2048 -e 128KiB -o jffs2.img
# nandwrite -p /dev/mtd0 jffs2.img
# mount -t jffs2 /dev/mtdblock0 /mnt/
# ls /mnt
bin boot dev etc lib linuxrc proc sbin tmp usr var

There is something wrong ?

      Truy cập Mail nhanh hơn! Yahoo! khuyến khích bạn nâng cấp trình duyệt lên Internet Explorer 8 mới, tối ưu hóa cho Yahoo!. Tải tại đây! 
http://downloads.yahoo.com/vn/internetexplorer/