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To: Poul-Henning Kamp <phk@phk.freebsd.dk>
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cc: Donn Miller <dmmiller@cvzoom.net>
cc: David Schultz <das@freebsd.org>
cc: fs@freebsd.org
Subject: Re: ideas about a unioning file system
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Poul-Henning Kamp wrote:

> The majority of the problems we have in this area can be nailed down
> to only two issues:
> 	1. The very tricky semantics of rename(2)
> 	2. read/write/mmap coherency for stacked filesystems.

This is of particular interest to me.  While Poul-Henning has
done some very interesting work on encryption at the GEOM
level, I'm trying to work with ACL filesystems and stacking
crypto filesystems that manage keys with one per file.

Imagine the coherency problems when pages don't match up
because of IVs for CBC block mode encryption, and imagine
the headache for (un-)locking pages at different levels.

Making it easy for FIST and cryptfs (Erez Zadok's stuff) would
be very helpful.  (I.e. gee, I'd rather not have to do this
on Linux).