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Re: [SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios

From: Gleb Natapov
Subject: Re: [SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios
Date: Tue, 12 Oct 2010 18:56:58 +0200

On Tue, Oct 12, 2010 at 09:33:16AM -0700, H. Peter Anvin wrote:
> On 10/12/2010 01:01 AM, Gleb Natapov wrote:
> > On Mon, Oct 11, 2010 at 02:15:26PM -0700, H. Peter Anvin wrote:
> >>> I don't disagree.
> >>>
> >>> I think the best thing to do is to let SeaBIOS create a boot order table 
> >>> that contains descriptive information and then advertise that to QEMU.
> >>>
> >>> QEMU can then try to associate the list of bootable devices with it's 
> >>> own set of devices and select a preferred order that it can then give 
> >>> back to SeaBIOS.  SeaBIOS can then present that list to the user for 
> >>> additional refinement.
> >>
> >> Really, this kind of comes down to having a data structure that anything
> >> (Qemu, SeaBIOS and if needed the guest OS) can read and modify as needed.
> >>
> > But then QEMU and seabios will have to have shared storage they can
> > both write too. And this shared storage is part of VM now so you need
> > to carry it around when you move your VM elsewhere.
> >  
> Yes, and it's part of real hardware, too.  It's usually called "the
> CMOS", short for CMOS RAM.
On real hardware it is not shared between HW and bios. It is
written/read only by BIOS. In qemu it is not persistent and generated
for each qemu invocation. Previously it was used to pass config params
from qemu to a bios (and some legacy params are still passed that way),
but we moved to better interface for that (firmware config).


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