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Date: Wed, 25 Nov 2009 11:09:58 +0100
From: Carsten Otte <carsteno@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 12/13] Add zipl bootloader interpreter
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To: Hannes Reinecke <hare@suse.de>
Cc: Carsten Otte <cotte@de.ibm.com>, Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, Mark Williamson <maw48@cantab.net>, Aurelien Jarno <aurelien@aurel32.net>

Hannes Reinecke wrote:
> So back to the zipl question, it might be an idea to support initially
> the SCSI disk layout only. This has the advantage of being far simpler
> as the DASD disk layout and should be pretty straightforward to handle.
Issue is, the dasd disk layout is made for dasds. For eckd, the boot 
code assumes variable blocksize, and the loader uses channel programs. 
For both eckd and fba volumes, it assumes IBM disklabels and FICON 
channel programs. Virt-IO disks do have an msdos-style partition table 
as opposed to this.
That said, you'd need proper virtualiztion of a ficon dasd so that the 
guest could possibly run the dasd boot code. Virt-IO disks otoh are 
fixed block, have an msdos-style partition table, no channel programs, 
and thus look just like scsi disks with a different interface. 
Therefore, I think scsi boot is right for virt-IO disks. And zipl does 
already create this layout in the version found in Sles11 and FC12.