Making the rootfs and /system writeable
mount -o rw,remount -t rootfs rootfs /
mount -o rw,remount -t yaffs2 /dev/block/mtdblock3 /system
Making the rootfs and /system readonly
mount -o ro,remount -t rootfs rootfs /
mount -o ro,remount -t yaffs2 /dev/block/mtdblock3 /system