Re: Mandatory vs. Advisory

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From: Stevan Steve Allen (scallen@us.ibm.com)
Date: 01/17/03-05:56:35 PM Z 

Subject: Re: Mandatory vs. Advisory
Message-ID: <OF87C77190.C41333AF-ON87256CB1.007D982A@us.ibm.com>
From: Stevan Steve Allen <scallen@us.ibm.com>
Date: Fri, 17 Jan 2003 15:56:35 -0800




David,

I believe your prior post describes a basic environment where applications
decide if locking (control) is needed and there is no checking by the pfs
level or file server.  In this environment, locking is never required by
the pfs/file server to access data (hence nothing to do with data
integrity).  The NFS supported locking model does not provide data
integrity, instead it is a communication vehicle for remote applications to
control each other.  Customers may attempt<?> to impose data integrity by
controlling access to only those applications which provide the necessary
lock requests for the level of integrity needed by the customer solution.

I have Brent's illustrated book (which we seem to have misinterpreted), do
you recommend any other material describing the control model you mention?

The application control model you describe below is not true in the
"locking" model we are familiar with.

"it is likely that you can take an application written for advisory locking
and have it work correctly with mandatory locking"

I suspect we are incorrectly imposed our locking model onto the NLM/v4
protocols.  Our prior experience comes from an required locking model
designed to guaranteed transactional data integrity in a shared
environment.  In our previous environment, locks were verified at the
remote pfs layer which may reject or provide implicit locking for a file
data request.  In such an environment, an application deciding not to lock
may be incompatible with the pfs layer access controls and fail.

Your application centered control model is interesting and I shiver at the
thought of removing the check in the remote pfs layer thereby allowing
possible data corruption due to a poorly coded application not protecting
data.  But hey, I'm open to new ideas.

Thanks,
Stevan C. Allen


                      Winston Churchill:
" A Riddle wrapped in a mystery inside enigma."

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