From owner-freebsd-stable  Mon Oct 30  8:37:48 2000
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From: Robert Nordier <rnordier@nordier.com>
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Subject: Re: Really odd "BTX halted" problem booting FreeBSD on VALinux hardware
To: obrien@FreeBSD.ORG (David O'Brien)
Date: Mon, 30 Oct 2000 18:19:18 +0200 (SAST)
Cc: dillon@earth.backplane.com (Matt Dillon),
	tlambert@primenet.com (Terry Lambert),
	freebsd-stable@FreeBSD.ORG (freebsd-stable@FreeBSD.ORG),
	hackers@FreeBSD.ORG
In-Reply-To: <20001030055307.B41250@dragon.nuxi.com> from "David O'Brien" at Oct 30, 2000 05:53:07 AM
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David O'Brien wrote:

> On Fri, Oct 27, 2000 at 01:10:56PM +0200, Robert Nordier wrote:
> > Just doing the disklabel -w -r followed by the disklabel -B is creating
> > a dangerously dedicated disk, 
> 
> Actually this is a "fully dedicated" disk.  (made to look like a 50MB or
> so disk to M$ products)
> Sysinstall is used to create a "dangeriously dedicated" disk (when not
> create slices.
 
I can't say I agree with the distinction (though I'm not sure it
really matters).

Consider this comment in sys/i386/i386/autoconf.c:

|  * For properly dangerously dedicated disks (ones with a historical
|  * bogus partition table), the boot blocks will give slice = 4, but
|  * the kernel will only provide the compatibility slice since it
|  * knows that slice 4 is not a real slice.  [....]

The "historical bogus partition table" is defined in the file
sys/kern/subr_diskmbr.c as follows:

| static struct dos_partition historical_bogus_partition_table[NDOSPART] = {
|       { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, },
|       { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, },
|       { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, },
|       { 0x80, 0, 1, 0, DOSPTYP_386BSD, 255, 255, 255, 0, 50000, },
| };

and this is the same table entry that appears in the hexdump provided
by Matt Dillon:

| Raw data on disk after 'disklabel -w -r da0 auto; disklabel -B da0 auto'
| 
| 000000f0  66 8b 46 08 52 66 0f b6  d9 66 31 d2 66 f7 f3 88  |f.F.Rf...f1.f...|
| . . . . .
| 000001e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 80 00  |................|
| 000001f0  01 00 a5 ff ff ff 00 00  00 00 50 c3 00 00 55 aa  |..........P...U.|

It's a long time since I used sysinstall, but I assume that a "fully
dedicated disk" just has a normal partition table with a single entry 
that allocates all available space.

The above, OTOH, is an illegal fdisk partition table entry, and what
I think most of us would refer to as "dangerously dedicated".

-- 
Robert Nordier

rnordier@nordier.com
rnordier@FreeBSD.org


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