From: "J. Bruce Fields" <bfields@fieldses.org>
Subject: Re: [PATCH] 64 bit ino support for NFS server
Date: Wed, 8 Aug 2007 17:01:04 -0400
Message-ID: <20070808210104.GO16171@fieldses.org>
References: <46B37DE6.80706@redhat.com> <46B38206.6050504@redhat.com>
	<20070804223256.GA1155@fieldses.org> <46BA2289.5060902@redhat.com>
	<20070808203555.GL16171@fieldses.org> <46BA2C3C.6040504@redhat.com>
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Cc: Neil Brown <neilb@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	NFS List <nfs@lists.sourceforge.net>
To: Peter Staubach <staubach@redhat.com>
In-Reply-To: <46BA2C3C.6040504@redhat.com>
Sender: nfs-bounces@lists.sourceforge.net
Errors-To: nfs-bounces@lists.sourceforge.net

On Wed, Aug 08, 2007 at 04:49:00PM -0400, Peter Staubach wrote:
> J. Bruce Fields wrote:
> > So Samba is holding a write lease on the file on behalf of one of its
> > clients.  We never see an open from our NFSv2/v3 client--if it doesn't
> > have data cached, we may never even see a read, just access and
> > getattr--so we don't know to break that lease.
> >
> > (Actually, if a write lease, like an NFSv4 write delegation, is meant to
> > cover file attributes as well as data, then perhaps stat should break
> > write leases.  That sounds painful.)
> >
> > Anyway, the delay between the time the Samba client makes a change and
> > the time the NFS client sees it could be unbounded.  Whereas with
> > lease_get_mtime() the client will invalidate its cache and perform a
> > read, which *does* break the lease (in nfsd_open).
> >
> > But I agree that this is a strange compromise, and I'd like to
> > understand better what the semantics for sharing with a Samba client are
> > supposed to be.
> 
> Yes.

There's a similar problem in the case of, say, a server with both a v3
and a v4 client.  If the v4 client has a write delegation, then we break
close-to-open semantics if the v3 client doesn't see change attribute
updates from the v4 client's local modifications.  So that's what we
have cb_getattr for.  And if you don't want to do cb_getattr calls then
I guess you should be breaking the lease.

--b.

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