Subject: [nfsv4] re: Mandatory

From: [email-masked]
Date: Thu, 22 Jan 2004 11:21:03 -0500 (EST)

Is there really a use for LOCK-WRITE-LOCKU, even if you extend the
protocol to support it?

If the server is applying mandatory locking to the file, the above would
imply the client can't cache the data. (Sec. 9.3.3) Given that, what is
the point of grabbing a Lock just for the duration of the Write?

Client just does Write:
Write will succeed or return NFSERR_LOCKED if there is a conflicting lock.

Client does Lock-Write-Unlock:
Will succeed, or fail with NFSERR_DENIED if there is a conflicting lock.
(I suppose there is an argument that the client knows about the conflicting
 lock for this case, but does it really care?)

The only purpose I can see for it would be to allow a client to ensure
that the write is "atomic" and not interspersed with a write of the
same region of the same file by another client. Would a client
that wants to ensure this not want a lock on the file's region for a
longer period of time?

I guess, in general, I get concerned when people start saying "We could
change this, then that could be done..." without asking if the added
capability is really needed by clients. (In other words "Hasn't the protocol
gotten complex enough yet?".)

rick

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