On Mon, 29 Sep 1997, William O Ferry wrote:

> Excerpts from mail: 29-Sep-97 Re: Problems with union mou.. by Brian C.
> Grayson@ece.ute 
> >   Since your concern is in mounting versions of the source tree,
> > you could use OBJDIR stuff, and thus make your source tree
> > read-only, right?  If so, mount_union allows NFS mounts.
> > In other words, mount_union doesn't enforce the check for whiteout
> > support if the upper layer is mounted readonly.  Would that do
> > the trick?
> 
>     I was able to union mount both the upper and lower layer provided
> they are done read-only.  The lower layer can be RO, it's only ever
> touched by sup on the remote host.  Ideally I'd like the top layer to be
> writable so that I can make my modifications without having to go to the
> other machine or even to a different mountpoint.  I assume there is no
> such way?
> 
	I'm afraid not - readonly is readonly... The options are as you
	state, go to a different machine, or mount it somewhere else
	'normally'.

>     Is there any way to get NetBSD to "re-export", so that I could just
> nfs mount the sparc's union-mounted /usr/src?  It seems that having the
> upper and lower layer on NFS will add a lot of traffic that I could get
> rid of if I could only just mount the remote mountpoint.  Though from
> some tests I've done, the i386 still compiles blazingly fast even when
> the source and destination are on NFS.
> 
	Not as far as I'm aware...

>     Forgive me for not understanding this, but what is whiteout support,
> and why doesn't NFS provide it?

	If you delete a file that exists in the lower level of a union
	filesystem, the upper level must somehow 'hide' the lower level
	file. This is done via a whiteout.

		David/abs

	-- Whom computers would destroy, they must first drive mad. --