Re: [Qemu-devel] Re: [PATCH 0/3]: Add UUID command-line option

[Jamie Lokier]

Anthony Liguori wrote:
> >>>CMOS has enough memory for UUID, but UUID is not the only thing that
> >>>needs to be passed to BIOS, so eventually we can run out of space there.
> >>> 
> >>>      
> >>I'm inclined to think that on a real machine, the UUID is stored in the 
> >>CMOS.
> >>    
> >
> >I'd imagine on a real machine the UUID cannot be changed, so it can't
> >be stored in the CMOS.  It's probably in the BIOS somewhere.
> >  
> 
> It may be part of the ROM that gets written to CMOS when you "reset to 
> factory defaults".  I can think of a number of advantages to storing it 
> in CMOS.

I thought the point of UUID is you're not supposed to be able to
change it on real hardware.  If it's in CMOS, and OSes/BIOS read it
from CMOS, then it's easy to change.

> >For testing guest ACPI implementations or changing their behaviour? :-)
> 
> Sounds like a fantastic way for a user to shoot themselves in the foot.

As if the other QEMU options are not like that :-)

> If you care to do this sort of work, you can certainly recompile the 
> BIOS.  The source is there afterall.

Indeed, same goes for all the other QEMU options.  The question is
whether it's useful enough to have an option, or obscure enough not to.

I'm inclined to think modifying ACPI tables is obscure, except
perhaps for specific tweaks that some versions of Windows or Linux
might need to run correctly, or to prevent them from using some
hardware feature or other.

-- Jamie