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SubjectRe: [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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