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Date:      Fri, 4 Oct 2002 20:21:29 -0400 (EDT)
From:      Robert Watson <rwatson@FreeBSD.ORG>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        Emiel Kollof <coolvibe@hackerheaven.org>, Peter Wemm <peter@wemm.org>, Poul-Henning Kamp <phk@critter.freebsd.dk>, n0go013 <ttz@blahdeblah.demon.co.uk>, current <freebsd-current@FreeBSD.ORG>
Subject:   Re: [ GEOM tests ] disklabel warnings and vinum drives lost
Message-ID:  <Pine.NEB.3.96L.1021004201933.64999K-100000@fledge.watson.org>
In-Reply-To: <Pine.NEB.3.96L.1021004200338.70577U-100000@fledge.watson.org>

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On Fri, 4 Oct 2002, Robert Watson wrote:

> On Fri, 4 Oct 2002, Terry Lambert wrote:
> 
> > The assumption here is that the devfs will be available to the system
> > before the root is mounted transparently over it.  This is also doable
> > with an unmounted instance of the backing devfs, not yet mounted on
> > /dev, if a transparent mount of / over top of a preexiting / -> /dev is
> > not supported (i.e. devfs is mounted on /dev on the root FS, rather than
> > the root FS being mounted on a backing node on which defvfs is already
> > mounted on /, and the devices showing through as if they were on /). 
> 
> Actually, no -- Vinum doesn't know how to do that--the device name used
> in this code originates in a userland ioctl() configuration call for
> Vinum. However, here's a patch that makes Vinum use namei() to rely on
> devfs to locate requested devices instead of parsing the device name and
> guessing the device number (incorrectly with GEOM).  Unfortunately, I
> almost immediately run into a divide by zero due to a zero sector size. 
> Jeff Roberson mentioned to me he had a fix for this bug that he sent to
> Greg, but that was never committed. 

On the general topic of access to devices before a root has been found,
Maxime Henrion <mux@FreeBSD.org> has done some interesting work on
'rootfs', a pseudofs used to bootstrap support for devfs, etc.  In such an
environment, Vinum and other consumers of devices would be able to rely on
devfs access prior to the "real root" mount process.  I'm not sure which
pivotroot-like trick he's using, or whether he's doing the union thing to
do the root re-mount.  Presumably he has to be careful not to deadfs the
devfs nodes in place before the real root turns up, etc. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories



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