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Date: Sun, 3 Oct 2004 14:32:37 -0400
From: David Schultz <das@FreeBSD.ORG>
To: Takanori Watanabe <takawata@init-main.com>
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cc: Uwe Doering <gemini@geminix.org>
Subject: Re: Your CVS fix 1.109 to union_vnops.c
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On Mon, Oct 04, 2004, Takanori Watanabe wrote:
> >With 'unionfs' you can have underlying files from two different layers 
> >(upper and lower) on two different file systems which may, by 
> >coincidence, have the same inode number.  Now, if you override the real 
> >va_fsid with that of the 'unionfs' mount you'll end up with two 
> >'unionfs' vnodes that appear to represent the same file (a hard link, 
> >for instance), but in reality the files are different entities. 
> >Obviously, both the kernel and applications might draw wrong conclusions 
> >in this case.
> 
> I think the three filesystem entry 
> 1. upper layer file
> 2. lower layer file
> 3. unionfs file
> can be treated as different.

I didn't pursue this before because I was concerned that it would
introduce cache consistency issues between the union vnode and the
underlying vnode.  But I guess all vnops ultimately wind up at the
underlying vnode, so this hopefully isn't an issue...