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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 1 Apr 2021 15:37:00 +0200
Message-ID: <CAJfpegtUOVF-_GWk8Z-zUHUss0=GAd7HOY_qPSNroUx9og_deA@mail.gmail.com>
Subject: overlayfs: overlapping upperdir path
To:     Amir Goldstein <amir73il@gmail.com>
Cc:     linux-fsdevel@vger.kernel.org,
        overlayfs <linux-unionfs@vger.kernel.org>,
        Vivek Goyal <vgoyal@redhat.com>
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Commit 146d62e5a586 ("ovl: detect overlapping layers") made sure we
don't have overapping layers, but it also broke the arguably valid use
case of

 mount -olowerdir=/,upperdir=/subdir,..

where subdir also resides on the root fs.

I also see that we check for a trap at lookup time, so the question is
what does the up-front layer check buy us?

Thanks,
Miklos