Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

From: Al Viro
Date: Tue Mar 22 2011 - 15:38:15 EST

On Tue, Mar 22, 2011 at 07:58:17PM +0100, Miklos Szeredi wrote:

> > > and its protection against renames is
> > > nowhere near enough. ??I might be missing something subtle, but...
> Protection is exactly as for userspace callers. AFAICT.

BTW, what filesystems can act as upper layers and how are you going to
prevent modifications of upper layer in normal way? It is mounted,
after all, or you would be unable to find it when mounting overlayfs.
And it might be mounted in any number of places, not all even visible to
you... I realize that you have it listed as a problem, but do you have
any ideas on how to deal with that?

If you allow NFS as upper layer, you really have a problem; with this
approach you probably want to prevent that very forcibly. Not that
your open() handling would work correctly with NFS, even with no modifications
from other clients or from server...
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