Re: [Qemu-devel] Re: [SeaBIOS] [PATCH 0/8] option rom loading overhaul.

[Anthony Liguori <anthony@codemonkey.ws>]

On 12/21/2009 01:43 PM, Gleb Natapov wrote:
> Please stop thinking so :) Especially about "user driven upgrades".
> Why combine disadvantages of vitalization with pain of physical HW
> management? Or may be next step will be to require uploading of CPU
> microcode to take advantage of KVM/tcg bug fixes?
>    

I think your real argument boils down to that we can be better than real 
hardware therefore we should.  I actually agree with you for 90% of 
users.  Let me summarize where I'm at.

  - We are currently horribly broken with respect to how we handle roms 
particularly with respect to backwards compatibility
  - We must support running older roms on newer qemu at least within a 
stable series (because of live migration)
  - We need a mechanism to include roms specific to a machine type
  - Probably by default, we want new roms to be used by guests at some 
well defined time (either first reset or first power-down/start-up)
  - We ought to make all roms live in qemu_ram_alloc()'d memory and we 
ought to change that api to contain contexts, this will make sure rom 
live migration works properly.

The best approach I can think of is to introduce an nvram mechanism.  A 
tar file probably work really well.  If a user doesn't supply an 
explicit -nvram, we could create a temporary file and delete it.  If the 
nvram is empty, we populate it with whatever the appropriate roms are 
for the machine type.

I would also suggest that we support the guest updating roms on its own 
(through fw_cfg).  I can think of a number of reasons for this.  For 
instance, why shouldn't a guest be able to update the gPXE associated 
with the network card?  The code runs entirely in the guest so there's 
no harm to the host.  Allow a guest to do this sort of thing takes 
pressure off of the management system so particularly in an environment 
like a cloud, I think this could prove very useful.

It could be possible to add an option to -nvram to make it re-read roms 
from disk every reboot.  I really think this is a bad idea though, I'd 
like to hear more people comment on it but it's certainly technically 
feasible.

Regards,

Anthony Liguori
> --
> 			Gleb.
>