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From: Michael Brown <mbrown@fensystems.co.uk>
Subject: Re: [Qemu-devel] OVMF, SeaBIOS & non-CSM based legacy boot
Date: Mon, 21 Mar 2011 21:17:55 +0000
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Jordan Justen <jljusten@gmail.com>, qemu-devel <qemu-devel@nongnu.org>

On Monday 21 Mar 2011 21:06:24 Stefan Hajnoczi wrote:
> On Mon, Mar 21, 2011 at 6:27 PM, Anthony Liguori <anthony@codemonkey.ws> 
wrote:
> > On 03/21/2011 01:14 PM, Jordan Justen wrote:
> >> This weekend I spent some time working on loading SeaBIOS from OVMF to
> >> start a legacy boot.  I was able to get x86&  x86-64 Linux to legacy
> >> boot using this method.
> >>
> >> Unfortunately, (I think) it is not nearly as nice a having a true CSM.
> >>  Basically, you have to decide at some point in the OVMF boot that you
> >> want to legacy boot, and once you start SeaBIOS running, OVMF/UEFI
> >
> > Interesting.  How much time does OVMF add to the total boot time when
> > taking this approach?
> >
> >> will never be in the picture again (until system reset).
> >>
> >> Contrast this to using a CSM where you can:
> >> * Load a legacy option ROM (vbios, or disk rom),
> >>   and use it during a UEFI boot
> >
> > Is there gPXE for UEFI yet?
> 
> I have never tried it myself, but I think it should work.  CCed
> Michael Brown to check.

Yes, iPXE for UEFI exists and works.  Last tested by me about a week ago, on 
various IBM UEFI systems.

Compared to a "legacy" BIOS network boot, you can't do anything very 
interesting with UEFI.  Features such as iSCSI, FCoE, AoE, HTTP all work with 
a "legacy" BIOS but not with UEFI.  A "legacy" BIOS network boot allows you to 
boot an operating system; a UEFI network boot only allows you to boot an EFI 
executable (which could be a second-stage OS loader).

UEFI as a platform has a long way to go before it matches the network boot 
functionality available through iPXE in a "legacy" BIOS.

Michael