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Re: [Xen-devel] PATCH 0/3: Direct linux kernel boot for HVM

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] PATCH 0/3: Direct linux kernel boot for HVM
From: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Date: Wed, 19 Dec 2007 13:00:36 +0000
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On Wed, Dec 19, 2007 at 10:48:13AM +0000, Keir Fraser wrote:
> On 19/12/07 05:38, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:
> > Those who saw Chris Wright give my Xen summit presentation a few weeks back
> > may remember one of the proposals was to support direct linux kernel boot
> > for HVM guests. ie, the ability to have a guest boot off a kernel, initrd,
> > and args instead of merely the BIOS supported disk/cdrom/network.
> Is the aim to be able to boot from any device that can be plumbed to qemu,
> or to allow kernel/initrd parms to be specified from outside the HVM
> bootloader config file? If the former, Anthony Liguori's recent patch to
> implement an option ROM to allow easy cut-thru to any qemu backend device
> looks like an easier way to achieve that aim.

It is the latter - just to allow boot from external kernl/initrd/params.
This is basically making 

   qemu-dm -kernel /path/to/vmlinux -initrd /path/initrd -append 'someargs'

work in Xen the same way it works in current upstream QEMU. 

Currently this hooks in QEMU's boot by writing a fake MBR into the first
harddisk. Once anthony's option ROM patch is accepted upstream they could 
be leveraged to get rid of the MBR hook (indeed anthony's patches include
this optimization). This is only a very minor part of the code though, so
the bulk of this patch would still remain.

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