Subject: [nfsv4] Lock fairness question

From: Frank S Filz <[email-masked]>
Date: Thu, 16 May 2013 14:17:18 -0700

RFC 3530 bis contains the following statement:

Some clients require the support of blocking locks. The NFS version
4 protocol must not rely on a callback mechanism and therefore is
unable to notify a client when a previously denied lock has been
granted. Clients have no choice but to continually poll for the
lock. This presents a fairness problem. Two new lock types are
added, READW and WRITEW, and are used to indicate to the server that
the client is requesting a blocking lock. The server should maintain
an ordered list of pending blocking locks. When the conflicting lock
is released, the server may wait the lease period for the first
waiting client to re-request the lock. After the lease period
expires the next waiting client request is allowed the lock. Clients
are required to poll at an interval sufficiently small that it is
likely to acquire the lock in a timely manner. The server is not
required to maintain a list of pending blocked locks as it is used to
increase fairness and not correct operation. Because of the
unordered nature of crash recovery, storing of lock state to stable
storage would be required to guarantee ordered granting of blocking
locks.

In this sentence: "The server should maintain an ordered list of pending
blocking locks." should is not capitalized. Is that intentional, that this
is advisory and not actually a requirement?

Thanks

Frank

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From: Marc Eshel <[email-masked]>
Date: Thu, 16 May 2013 14:38:06 -0700

later in this paragraph it says 

" The server is not required to maintain a list of pending blocked locks 
as it is used to
increase fairness and not correct operation."

Marc.

From:   Frank S Filz/Beaverton/IBM@IBMUS
To:     [email-masked], 
Date:   05/16/2013 02:18 PM
Subject:        [nfsv4] Lock fairness question
Sent by:        [email-masked]

Thanks

Frank_______________________________________________
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