Re: [Qemu-devel] Re: [PATCH 0/2] port over extboot from kvm

[Anthony Liguori]

Avi Kivity wrote:
> On 09/08/2009 05:32 PM, Anthony Liguori wrote:
> > Gerd Hoffmann wrote:
> > > On 09/08/09 15:47, Jan Kiszka wrote:
> > >
> > > > Before setting this definitely useful feature in stone, I have two
> > > > questions though:
> > > >
> > > >   - -drive ...,boot=on is logically in conflict with -boot. Yes, -boot
> >
> > x86 boot is strange.  The BIOS boots from the "first hard disk"  What 
> > extboot allows you do to is redefine to the bios what constitutes the 
> > "first hard disk".
>
> It's not just booting - it's the int 0x13 interface.  Grub for example 
> continues to use it and can boot from the second hard disk if desired.

Our BIOS can only support booting from the 0x80 and this is pretty normal.

The right way to do this from a BBS perspective would be to implement 
BCV support.  We could then have BCV entries for every possible disk.  
Option roms (like extboot/gpxe) can register add new BCV entries.  We'd 
want the user to be able to specify the priority of each disk, so..

> I agree with this and I think we should extend it to 
> boot=0x80|0x81....  boot=on is an alias to boot=0x80.

Would be better to stick with 0-based integers.  We would then use this 
to generate BCV priorities.

The highest priority BCV device is still exposed as int13 disk 0x80.  I 
suspect certain OSes will only boot from disk 0x80 (probably Windows).

Regards,

Anthony Liguori