linux-kernel - Re: [PATCH 0/5] hybrid union filesystem prototype

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Date:	Tue, 31 Aug 2010 15:18:46 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Miklos Szeredi <miklos@...redi.hu>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Neil Brown <neilb@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	jblunck@...e.de, hch@...radead.org
Subject: Re: [PATCH 0/5] hybrid union filesystem prototype

On Mon, Aug 30, 2010 at 02:20:47PM +0200, Miklos Szeredi wrote:
> On Mon, 30 Aug 2010, Neil Brown wrote:
> 
> > Val has been following that approach and asking if it is possible to make an
> > NFS filesystem really-truly read-only. i.e. no changes.
> > I don't believe it is.
> 
> Perhaps it doesn't matter.  The nasty cases can be prevented by just
> disallowing local modification.  For the rest NFS will return ESTALE:
> "though luck, why didn't you follow the rules?"

I agree: Ask the server to keep it read-only, but also detect if it
lied to prevent kernel bugs on the client.

Is detecting ESTALE and failing the mount sufficient to detect all
cases of a cached directory being altered?  I keep trying to trap an
NFS developer and beat the answer out of him but they usually get hung
up on the impossibility of 100% enforcement of the read-only server
option. (Agreed, impossible, just give the sysadmin a mount option so
that it doesn't happen accidentally.)

-VAL
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