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

[Sebastian Herbszt]

Anthony Liguori wrote:
> 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)

Start-up sounds good.

>  - 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.

You mean the nvram file on the host or in memory? Will there be a size limit?

> 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 might not be desired and make support efforts harder. Could have security
implications too.

> 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.

- Sebastian