Subject: Re: another nfs puzzle
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Peter Staubach <staubach@redhat.com>
Cc: Kenny Simpson <theonetruekenny@yahoo.com>, linux-kernel@vger.kernel.org
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	 <1133964667.27373.13.camel@lade.trondhjem.org>  <4396EF50.30201@redhat.com>
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Date: Wed, 07 Dec 2005 09:34:22 -0500
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On Wed, 2005-12-07 at 09:18 -0500, Peter Staubach wrote:
> >In this context it doesn't matter whether or not the you use the same
> >file descriptor. The problem is the same if my process opens the file
> >for O_DIRECT and then your process open it for normal I/O, and mmaps it.
> >
> 
> Yup, same problem.  Why is this allowed?  Does it really work correctly?

Assuming that the processes have _some_ method of synchronisation, then
I cannot see why it shouldn't be workable. Come to think of it, it might
even be possible to use O_DIRECT to provide that synchronisation (use
O_DIRECT to set a "lock" on the page, then modify it using mmap). 

Whether or not there are people out there that actually _want_ to do
this is a different matter.

Cheers,
  Trond

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