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From: Doug Rabson <dfr@rabson.org>
To: Kirk McKusick <mckusick@mckusick.com>
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Date: Sat, 12 Apr 2008 18:24:11 +0100
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Subject: Re: VOP_LEASE 
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On 12 Apr 2008, at 18:03, Kirk McKusick wrote:

>> Date: Sat, 12 Apr 2008 02:13:15 -1000 (HST)
>> From: Jeff Roberson <jroberson@jroberson.net>
>> To: arch@freebsd.org
>> Subject: VOP_LEASE
>>
>> As far as I can tell this has never been used.  Unless someone can  
>> show me
>> otherwise I'm going to go ahead and remove it.
>>
>> Thanks,
>> Jeff
>
> VOP_LEASE is used by NQNFS and NFSv4. It notifies them when a file
> is modified locally so that they know to update any outstanding
> leases (e.g., evict any write lease for the file and do callbacks
> for any read leases for the file). Deleting VOP_LEASE would break
> NFS big time.

I think our NQNFS support might have been removed some time ago - I  
can't see any calls to VOP_LEASE in the code right now. Something like  
VOP_LEASE would certainly be useful for a hypothetical future NFSv4  
server. I believe that samba could use it too for its oplocks feature  
which appears to be similar to NQNFS's leases and NFSv4's delegations.