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Date: Mon, 11 Mar 1996 07:53:04 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199603102053.HAA14288@godzilla.zeta.org.au>
To: bde@zeta.org.au, rgrimes@GndRsh.aac.dev.com
Subject: Re: booting from sd5 when wd3 is also installed
Cc: current@freebsd.org
Sender: owner-current@freebsd.org
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>> I haven't decided exactly how to handle these points:
>> - how sticky should the drive number be?  What is the default drive number
>>   after 1:sd(0,a)/nonesuch followed by /kernel?

>IMHO, 0.  Does ``1:?'' or even ``1:xx(y,z)/kernel?'' work?

I had `1:' by itself working for a while, but decided that it shouldn't
be so easy to change the BIOS number without changing the unit number,
so I made `1:' only work with `xx(y,z)'.  `1:xx(y,z)any' should work.
`xx(y,z)any' works the same as now - the BIOS drive number is set to
match `y'.  This isn't the best behaviour (you often want to keep the
BIOS boot drive number and change the FreeBSD unit number) but it is
required for compatibility and is the best behaviour for changing the
drive type from fd to sd.

>I can't test them, but have a small nit I found doing a visual over the
>context diff.... ohh... and can you bounds check the BIOS drive number

Thanks.

>against the number of drives reported by the BIOS, I seem to recall
>an infinite error loop if you did something like wd(1,a)/kernel with
>only one BIOS drive.

It's still easy to get these.  I got a lot when I forgot to subtract
'0' from the drive number :-).

Does the BIOS report the number of drives reliably?  The byte at
physical 0x475 seems to correctly give the total number of non-floppy
drives here (not the number of wd drives like I once thought).

BTW there is a bug in `gdb -k /kernel /dev/mem': gdb loops internally
for `p/x *(int *)0xf0000475'; it ignores ^C but can be suspended.

Bruce