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Date: Wed, 30 Jul 1997 13:06:06 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199707300306.NAA28631@godzilla.zeta.org.au>
To: bde@zeta.org.au, rgrimes@GndRsh.aac.dev.com
Subject: Re: Multiple FreeBSD Systems on a Single Disk
Cc: abial@korin.warman.org.pl, current@FreeBSD.ORG, sherwink@ix.netcom.com
Sender: owner-freebsd-current@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

>> That would mainly break certain configurations.  The active flag
>> should only be set for one partition, so you shouldn't have any active
>> FreeBSD partitions if you have an active DOS partition.
>
>Right, and if I have an active DOS partition the BIOS is going to
>boot the ACTIVE dos partition.  It won't even load the BSD boot
>blocks if that is not the active partition.
>
>Any configuration that was broken by this change was broken such
>that the BIOS should have not even booted anything!  The BIOS should

Only most configurations.

>have returned a ``No Active Partition'', or gone on to the next
>disk drive (yes, AMI bios'es as old as 1982 can boot from drive
>0x81 if there are no active partitions on drive 0x80.)

Booting is mostly handled by the bytes in the MBR, which have nothing
to do with the BIOS.  I believe BIOSes that support booting from any
disk look at the 0xAA55 boot signature and not at the active flag.
There is no active flags for floppies (unless the MBR supports them).

>> This should be fixed by adding slice support to the boot loader's
>> name parser.  Then you could bounce off the first FreeBSD to any other
>> slice by putting a boot loader on the first slice and configuring it
>> to boot from slice sN, e.g., "0:sd(0,s5,a)kernel" to boot the first
>> logical drive on an extended slice.

>Poppy cock, the active flag model should work and not require the
>addition of slice choosing support to the boot blocks.  OSBS and
>other multiboot loaders will infact set the chosen partition to
>active, it is just the brain damaged FreeBSD boot code that ignores
>the active flag, and chooses the FIRST BSD parition it finds
>no matter what, which is _WRONG_.

The active flag model only works when the MBR supports it, and it is
less flexible.  In the active flag model, the default boot slice is
stored as an active flag, and non-defaults are specified by typing the
slice number and passing the choice to the secondary boot loader.  In the
configured boot lader model, the default boot drive, slice, partition
and kernel name is stored in /boot.config in the first FreeBSD slice, and
non-defaults are specified by typing them at the secondary boot prompt.

Bruce