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To: Jeff Roberson <jroberson@jroberson.net>
Date: Sun, 13 Apr 2008 13:18:04 -0700
From: Kirk McKusick <mckusick@mckusick.com>
Cc: arch@freebsd.org
Subject: Re: VOP_LEASE 
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The explanation is correct that VOP_LEASE is present so that an NFS
server is made aware when a file is used locally so that the server
can take appropriate action on the leases that it has extended to its
clients.

Because VOP_LEASE is not under a lock, the race that Jeff points out
is also valid. To be race-free, they would need to be protected by
the vnode lock. Most instances of them are still protected by the
vnode lock, though some key ones (like READ and WRITE) fell out
of being protected when the vnode lock was pushed down so that it
no longer protected f_offset updates.

Using the pre- and post- hooks in the vnode operations would be an 
equally valid place to do the leasing call-back to the NFS (or other
remote filesystem) server. As the VOP_LEASE calls were, at least at 
the time they were in use, correctly placed and indentified read or 
write access, it might be useful to figure out the appropriate set
of pre- and post- hooks as part of their removal.

	Kirk McKusick