From owner-freebsd-fs  Sun Sep 13 00:02:03 1998
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Date: Sun, 13 Sep 1998 00:01:42 -0700 (PDT)
From: Don Lewis <Don.Lewis@tsc.tdk.com>
Message-Id: <199809130701.AAA22846@salsa.gv.tsc.tdk.com>
To: freebsd-fs@FreeBSD.ORG
Subject: vm system interaction with nullfs
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Since the vm system keeps track of what it has in memory by (vnode, offset),
how is this supposed to work when stackable filesystems are in use which
create multiple vnodes for a single filesytem object, or is this broken?
Unless this works right, it looks like you'll end up with multiple copies
of the same disk blocks in memory and in memory copies may all be different.

It would seem that in the case of nullfs and similar transparent filesytems,
the vm system should always use the lowest vnode, but this doesn't seem to
be implemented (though I could just be getting lost in the maze of twisty
little passages).  It's even messier if the layer isn't transparent,
like an encryption layer.


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