Date: Sun, 3 Oct 2004 14:32:37 -0400 From: David Schultz <das@FreeBSD.ORG> To: Takanori Watanabe <takawata@init-main.com> Cc: Uwe Doering <gemini@geminix.org> Subject: Re: Your CVS fix 1.109 to union_vnops.c Message-ID: <20041003183237.GA8100@VARK.MIT.EDU> In-Reply-To: <200410031805.i93I5JNZ009076@sana.init-main.com> References: <41601BE0.4050401@geminix.org> <200410031805.i93I5JNZ009076@sana.init-main.com>
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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...
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