dd if=/dev/zero of=new_fs bs=1M count=4
./linux ubd0=... ubd1=new_fs ...
usermode:~# ls -l /dev/ubd total 0 brw-rw---- 1 root root 98, 0 Dec 31 1969 0 brw-rw---- 1 root root 98, 1 Dec 31 1969 1
/projects/cs378.ygz/bin/mkdosfs -S 1024 -v /dev/ubd/1
mkfs.minix /dev/ubd/1
mkfs.ext2 /dev/ubd/1
mkdir /mnt/test
mount /dev/ubd/1 /mnt/test
struct xxxxx_operations
struct dentry * root, * pwd
struct file ** fd