linux-kernel - Re: [PATCH 2/2] NFSv4: Return the delegation if the server returns NFS4ERR

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Message-ID: <1331239814.11759.1.camel@lade.trondhjem.org>
Date:	Thu, 8 Mar 2012 20:50:14 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
CC:	Olga Kornievskaia <aglo@...i.umich.edu>,
	Miklos Szeredi <miklos@...redi.hu>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] NFSv4: Return the delegation if the server returns
 NFS4ERR_OPENMODE

On Thu, 2012-03-08 at 15:42 -0500, J. Bruce Fields wrote:
> On Thu, Mar 08, 2012 at 03:23:34PM -0500, Olga Kornievskaia wrote:
> > On Thu, Mar 8, 2012 at 1:15 PM, Myklebust, Trond
> > <Trond.Myklebust@...app.com> wrote:
> > > On Thu, 2012-03-08 at 12:52 -0500, Olga Kornievskaia wrote:
> > >> wouldn't it be better for you to proactively return a read delegation
> > >> then unnecessarily erroring?
> > >
> > > If nobody else holds a delegation, then the NFS client is actually
> > > allowed to keep its read delegation while writing to the file. It does
> > > admittedly need to request an OPEN stateid for write in that case...
> > > (See section 10.4 of RFC3530bis draft 16)
> > 
> > If we both agree that there has to be a request for an open stateid for
> > a write, then instead of returning the read delegation if the client receives
> > err_openmode (when it send the request with read delegation stateid
> > as you said per 3560bis), can't the client resend the setattr with the open
> > stateid? The ordering of the stateid usage is a "should" and not a "must".
> > 
> > In rfc5661, it really doesn't make sense to ever send a setattr with
> > a read delegation stateid. According to 9.1.2, the server "MUST" return
> > err_open_mode" error in that case.
> > 
> > I gather you are in this case dealing with 4.0 delegations. But I wonder
> > if you'll do something else for 4.1 delegation then?
> 
> 3530bis has the same language ("...must verify that the access mode
> allows writing and return an NFS4ERR_OPENMODE error if it does not").

OK, so we shouldn't send the delegation stateid either for v4 or v4.1.
However should we pre-emptively return the delegation? I've been
assuming not.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com