1. 4.3 Network File System (NFS)
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2. NFS architecture
vnodes
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3. Vnode Data fields (struct vnode) Methods (struct vnodeops) inode/rnode
v_flag
vfsp
v_count
v_type
v_vfsmountedhere …
v_data
v_op
FS-dependent
implementation of vnodeops
vop_open vop_lookup
vop_read vop_mkdir
vop_getaddr …
FS-independent part
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4. vnode/vfs framework Client application System call interface vnode
nsf_vnodeops
v_data
v_ops
r-node
(contains file handle)
RPC call
NFS
client
code
RPC
client
interface
RPC reply
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5. NFS server implementation (ufs server)
vnode
ufs_vnodeops
v_data
v_ops
ufs-inode
NFS
server
code
ufs
code
RPC call
RPC
server
interface
RPC reply
local disk
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6. FS ID inode # inode generation #
VFS layer
FS ID inode # inode generation #
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7. Server interface (text Fig. 8.9)
lookup(dirfh, path-name)  fh, attr
attr= mode (e.g., read-only), user_id, group_id, size, access time, file system ID, etc.
create(dirfh, name, attr)  fh, attr
Argument and return attr are different sets
remove(dirfh, name)  status
read(fh, offset, count)  attr, data
write(fh, offset, count, data)  attr
rename(dirfh, name, 2dirfh, 2name)  status
setattr(fh, attr)  attr
New in V4
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8. NFS daemons Client Server write( ) User User Kernel Kernel nfsd nfsiod2 1
User
Kernel
User
Kernel
nfsd
nfsiod 3 4 5
Disk
Asynchronous writes (1,2) at client
Write (3) on close, synch, and every 30 sec
Server either (a) puts it in cache, or (b) writes-through.
Write-through (synchronous writes) (3,4,5) on commit (=close)
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9. Read-ahead and delayed write
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10. Cache consistency
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11. TTL (Time-to-Live) and validation
file
TTL=3sec
delayed write (< 30sec)
Server
TTL=30sec
write-thru
directory
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12. Stateless server (V3)
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13. Pathname lookup in V3
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14. Review: Mounting in vfs/vnode architecture
Root file
system
Mounted
file system
rootvfs
covers
belongs to
ROOT
mounted
here
ROOT /
/usr /
vnode
vnode
vnode
Vnodes for mounted-on directories and mounted roots
are kept in MM.
nov16
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15. Mounting example
Server 1
Server 2
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16. Mounting on top of imported directory
Server 1 (S1)
Server 2 (S2)
Importing from S1
Importing from S2
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17. Two file systems at the same server
Server1 exports
/usr and
/usr/local
(Exporting /usr
doesn’t autom-
atically export
/usr/local).
Similarly for
importing.
In V3, readdir on
fh for local returns
its original contents
disk0 /
usr u1
local f1 f2 /
disk1 f3 f4
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18. continued … Lookup for /usr/local/f3 !=
Cannot pass entire path to Server1. f3 f3 /
usr u1
local f1 f2 f3
mount –t nfs Server1:/usr /usr
mount –t nfs Server2:/local /usr/local
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19. Mount permission
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20. Automount
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21. Automount example /etc/auto_home contains
tiko server1:/export/home/tiko
john server2:/export/home/john
When /home/tiko is accessed for the first time on any machine (at log-in time), server1:/export/home/tiko is mounted on local /home/tiko
This way, I can log on to any machine and have the same /home/tiko environment.
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22. Important NFS V3 properties
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23. Version 4
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24. Version 4 pathname lookup
orange:/export/vol1
Request
putrootfh
lookup “export/vol1”
getfh Get fh for /export/vol1
getattr
Response
 putrootfh OK CURFH
lookup OK CURFH
getfh OK
getattr OK
Returned FH for orange:/export/vol1 can be cached at client’s machine.
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25. Reading orange:/export/vol1/home/data
 putfh fh fh is file handle for /export/vol1
open “home/data”
read at 0 for 1024
 putfh OK CURFH
open OK CURFH
read OK (1024 bytes)
NFS V4 itself has no concept of mounting.
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26. Pathname lookup failure
ls /export/home/fake
putrootfh
lookup “export” “home” “fake”
getfh
getattr
If fake doesn’t exist, response would be
 putfh OK CURFH
lookup FAILED
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27. Component-wise pathname lookup
Client can then resort to component-by-component resolution
putrootfh
lookup “export”
getfh
getattr
lookup “home”
lookup “fake”
Response from server
putrootfh OK CURFH
lookup OK CURFH
getfh OK
getattr OK
lookup FAILED
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28. Component-wise lookup
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29. Compound procedure
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30. V4 file locking
lock:
lockt:
locku:
renew:
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31. V4 server crash recovery
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32. Duplicates elimination upon RPC failures
Three situations for handling retransmissions.
The request is still in progress
The reply has just been returned
The reply had been sent some time ago, but was lost.
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