Re: [nfsv4] Read delegations and LOCK operation

[Trond Myklebust <trond.myklebust at fys.uio.no>]

On Thu, 2009-10-29 at 11:52 -0400, Rick Macklem wrote:
> 
> On Wed, 28 Oct 2009, Noveck, Dave wrote:
> 
> >> Mandatory byte range locking requests that there
> >> always be a byte range lock that encompasses the
> >> byte range a process or client reads or writes.
> >
> > Can you point me to something that says that?  I've been googling
> > looking for some clear specification of what mandatory byte range locks
> > actually do, but this seems hard to believe.  It means that if you set
> > the mode bits indicating mandatory locking, you can't do an ordinary
> > read of the file; you would need a special program that did locks around
> > the reads.
> >
> I believe Mike was referring to Sec. 9.3.3 of rfc3530, which requires
> clients to hold byte range locks for byte ranges being cached.
> --> The I/O is allowed, but can't be cached unless the range is locked
>      by the client.

There is absolutely no reason for a posix based client to obey that if
it holds a read delegation.

So what if a non-posix client can grab an exclusive lock on the file? It
still can't actually modify the data without causing the delegation to
be recalled first.

Cheers
   Trond