"Reverse union" mount possible?

[Erez Zadok]

In message <20031121005706.GA67377 at wombat.robbins.dropbear.id.au>, Tim Robbins writes:
> On Thu, Nov 20, 2003 at 02:41:43PM +0300, Alex Povolotsky wrote:

[...]
> > Right now, I'm readonly mount_null'ing /bin, /sbin, /usr/bin, /usr/sbin,
> > /usr/lib, /usr/include, /usr/libexec, /usr/share. With a dozen jails, there
> > are too many mounts to my liking, and about twice a week I experience panic.
> > Probabily it's nullfs-related.
> 
> Nullfs is known to be buggy in -stable. In particular, it seems to deadlock
> under load / when vnodes start getting recycled.

My fist stackable templates were ported to fbsd 4.x and 5.0 not too long
ago.  We ran extensive tests to ensure that the code is stable.  While it's
possible we missed stuff, it might help if someone checked what is different
about my "wrapfs" vs. Nullfs.  We may have fixed bugs in wrapfs not
realizing that they originally came from the base Nullfs we started with.

Cheers,
Erez.