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Date: Tue, 28 Oct 2014 22:54:28 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Tim Tassonis <stuff@decentral.ch>
Cc: linux-kernel@vger.kernel.org
Subject: Re: overlayfs: "filesystem of lowerdir is not supported" on cdrom
Message-ID: <20141028225428.GC7996@ZenIV.linux.org.uk>
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On Tue, Oct 28, 2014 at 09:13:13PM +0000, Al Viro wrote:

> Documentation is wildly over-optimistic.  You are trying to use something
> with non-trivial ->d_hash and ->d_compare as lower layer.
> 
> What should happen if you ask to mount an image with joliet extensions and
> ask to create foo.txt.... when foo.txt is there?  From the isofs POV those
> are the same; for overlayfs they are not (it's using default ->d_hash
> and ->d_compare).
> 
> We probably ought to split the normal (case-sensitive, no joliet shite) case
> out and leave it with NULL ->s_d_op, but that'll need to be done carefully,
> or isofs_cmp() will blow up on us.

See if vfs.git#for-linus works for you.