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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Fri, 28 Jan 2022 17:24:15 +0200
Message-ID: <CAOQ4uxhMBZBE1dBZJ6S5MfhCNCZ2NdDpzuQyR7rp4J6gyp6p_Q@mail.gmail.com>
Subject: Re: [PATCH v2] fs: rename S_KERNEL_FILE
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     David Howells <dhowells@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Chaitanya Kulkarni <chaitanyak@nvidia.com>,
        Miklos Szeredi <miklos@szeredi.hu>
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On Fri, Jan 28, 2022 at 3:17 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Fri, Jan 28, 2022 at 11:35:59AM +0000, David Howells wrote:
>
> > > Whether deny rmdir should have its own flag or not I don't know,
> > > but from ovl POV I *think* it should not be a problem to deny rmdir
> > > for the ovl upper/work dirs as long as ovl is mounted(?).
> >
> > What's the consequence of someone rearranging the directories directly in the
> > contributing dirs whilst there's an overlay over them?
>
> "Don't do it, then - presumably the kernel won't panic, but don't expect it to
> try and invent nice semantics for the crap you are trying to pull"

IIUC, I think that is the point Dave was trying to make.
Nothing good can come out of allowing users to manipulate the overlay
upper/work dirs, so denying rmdir on those dirs that are already marked
with the OVL_INUSE flag is probably not a bad idea anyway, so ovl
and cachefiles could potentially use the same flag with same semantics.

Thanks,
Amir.