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Date: Tue, 08 Sep 2009 14:46:33 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: [PATCH 0/2] port over extboot from kvm
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To: Avi Kivity <avi@redhat.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org

Avi Kivity wrote:
> The bios exports the "bios drives".  You can tell grub to load a 
> kernel from the first partition of the second disk: (hd1,0) or even 
> chain-load another boot loaded from another disk.

The whole point of device.map is that grub doesn't intrinsically know 
how to map from bios drives to real drives.  In fact, when you 
chain-load with grub, you often have to "swap" device mappings which has 
the effect of hooking int13 and faking the primary drive for another 
OS.  See 
http://www.gnu.org/software/grub/manual/html_node/DOS_002fWindows.html

All else aside, from a BIOS perspective, you can usually only boot from 
0x80 and that can be mapped to different drives via BCV.

Regards,

Anthony Liguori