From: Trond Myklebust <Trond.Myklebust@netapp.com>
Subject: Re: inconsistent mount attributes (ro/rw), RHEL5 / Netapp
Date: Mon, 14 May 2007 12:06:14 -0400
Message-ID: <1179158774.6474.18.camel@heimdal.trondhjem.org>
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Cc: nfs@lists.sourceforge.net, Ian Kent <raven@themaw.net>
To: Paul Krizak <paul.krizak@amd.com>
In-Reply-To: <46488696.9080009@amd.com>
Sender: nfs-bounces@lists.sourceforge.net
Errors-To: nfs-bounces@lists.sourceforge.net

On Mon, 2007-05-14 at 10:56 -0500, Paul Krizak wrote:
> > We might then be able to add an '--unshared-cache' option (any
>  > suggestions for a better name?) to mount in order to allow those people
>  > who fully understand the consequences to override, and hence to mount
>  > the same filesystem with different mount options, but no sharing of the
>  > page cache with the original filesystem.
> 
> I can assure you that AMD systems engineering would *much* prefer having 
> the VFS stack fixed such that we don't need to do something like this.
> 
> It would be much better to make the kernel understand that it *can* 
> mount the same NFS filesystem twice, once read-only and again 
> read-write, with the appropriate cache coherency, rather than force us 
> to run in a potentially dangerous configuration that might lead to data 
> corruption.
> 
> I agree with Ian that the VFS changes need to take priority.  The only 
> change I see that needs to be made to mount is that it needs to spit out 
> a warning (or fail completely) if the requested options cannot be satisfied.

I agree that the read-only flag need to be fixed at the VFS level. I
wasn't talking about that.

I'm talking about people who want to force different security flavours
on different paths for the same filesystem, or who want to set different
rsize/wsize, attribute timeouts etc. There are applications that might
benefit from that, and that do not care about sharing caches (either
because they know that there are no cross-linked files, or because they
are using a locking system that can deal with the cache consistency
issue).

Trond

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