Lab08 filesystems

[maranicolae]

Laborator 8

myfs

Exercitiul 1

Structura file_system_type a fost initializata pentru sistemul de fisiere virtual myfs. In functia de mount specifica acestuia am folosit mount_nodev intrucat filesystem-ul este virtual si nu are nevoie de suport fizic. In functiile de init si exit ale modulului am inregistrat/eliminat sistemul de fisiere.

Corectitudinea implementarii am verificat-o prin urmatoarea serie de comenzi in masina virtuala:

root@qemux86:~/skels/filesystems/myfs# insmod myfs.ko
myfs: loading out-of-tree module taints kernel.
register_filesystem successful
root@qemux86:~/skels/filesystems/myfs# cat /proc/filesystems | grep myfs
nodev   myfs
root@qemux86:~/skels/filesystems/myfs# mkdir -p /mnt/myfs
root@qemux86:~/skels/filesystems/myfs# mount -t myfs none /mnt/myfs
root inode has 1 link(s)
mount: mounting none on /mnt/myfs failed: Not a directory

Exercitiul 2

In structura de tipul super_operations am definit functiile superblock-ului utilizandu-le pe cele generice generic_delete_inode() si simple_statfs() pentru o functionalitate minimala. Dupa aceea am completat functia fill_super completand restul campurilor din superblock.

Exercitiul 3

Completand functia myfs_get_inode am initializat inode-ul radacina. Prelunad informatiile din namespace-ul root am completat campurile uid, gid si mode ale inode-ului. Fiind un director, am adaugat operatiile specifice si am incrementat numarul de link-uri.

Exercitiul 4

Corectitudinea rezolvarii se poate observa din outputul urmator:

root@qemux86:~/skels/filesystems/myfs# mkdir -p /mnt/myfs
root@qemux86:~/skels/filesystems/myfs# mount -t myfs none /mnt/myfs
root inode has 2 link(s)
root@qemux86:~/skels/filesystems/myfs# cat /proc/mounts | grep myfs
none /mnt/myfs myfs rw,relatime 0 0
root@qemux86:~/skels/filesystems/myfs# ls -di /mnt/myfs/
   4282 /mnt/myfs/
root@qemux86:~/skels/filesystems/myfs# stat -f /mnt/myfs
  File: "/mnt/myfs"
    ID: 0        Namelen: 255     Type: UNKNOWN
Block size: 4096
Blocks: Total: 0          Free: 0          Available: 0
Inodes: Total: 0          Free: 0
root@qemux86:~/skels/filesystems/myfs# ls -la /mnt/myfs
drwxr-xr-x    2 root     root             0 Apr 30 12:52 .
drwxr-xr-x    3 root     root          1024 Apr 28 10:36 ..
root@qemux86:~/skels/filesystems/myfs# touch /mnt/myfs/a.txt
touch: /mnt/myfs/a.txt: Permission denied
root@qemux86:~/skels/filesystems/myfs# umount /mnt/myfs

minfs

Exercitiul 1

In functia de mount myfs_mount am folosit mount_bdev intrucat filesystem-ul este nu mai este virtual ci are nevoie de suport fizic. Campul fs_flags al structurii de tipul file_system_type are valoarea FS_REQUIRES_DEV pentru a indica un filesystem ce utilizeaza un disk.

Verificam ca filesystem-ul a fost creat cu succes:

root@qemux86:~/skels/filesystems/minfs/kernel# cat /proc/filesystems | grep minfs
nodev   minfs

Exercitiul 2

Cu ajutorul functiei sb_bread citim block-ul de la index 0, campului b_data i se face cast la structura de tip superblock struct minfs_super_block (structura custom) si se verifica valoarea magic number-ului. Se copiaza valorile obtinute in superblock-ul generic si in structura de tipul struct minfs_sb_info.

Exercitiul 3

Am completat functiile minfs_alloc_inode populand campul vfs_inode al structurii alocate folosind functia inode_init_once. Conform functiei utilizate,initializare se face o singura data, campurile inode-ului fiind idempotent (nu se modifica in urma operatiilor). Apoi am completat functia de dezalocare asociata.

Exercitiul 4

Cu ajutorul functiei sb_bread citim block-ul de la index 1, apoi extragem inode-ul de index-ul ino. Am completat campurile uid, gid, mode si size ale variabilei inode (VFS inode). In cazul in care inode-ul este director, atunci se completeaza si campurile i_op si i_fop si incrementam numarul de link-uri.

Acum inlocuim apelul functiei myfs_get_inode cu aceasta functie minfs_iget.

Exercitiul 5

Testam corectitudinea implementarii:

Setup:

root@qemux86:~/skels/filesystems/minfs/user# ./mkfs.minfs /dev/vdd
root@qemux86:~/skels/filesystems/minfs/user# cd
root@qemux86:~# cd skels/filesystems/minfs/kernel/
root@qemux86:~/skels/filesystems/minfs/kernel# insmod minfs.ko
minfs: loading out-of-tree module taints kernel.
root@qemux86:~/skels/filesystems/minfs/kernel# mkdir -p /mnt/minfs/

root@qemux86:~/skels/filesystems/minfs/user# ./test-minfs.sh
+ insmod ../kernel/minfs.ko
+ mkdir -p /mnt/minfs
+ ./mkfs.minfs /dev/vdb
+ mount -t minfs /dev/vdb /mnt/minfs
released superblock resources
mount: mounting /dev/vdb on /mnt/minfs failed: Not a directory
root@qemux86:~/skels/filesystems/minfs/user#