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

[Anthony Liguori]

Gleb Natapov wrote:
> On Sun, Dec 20, 2009 at 08:58:40AM -0600, Anthony Liguori wrote:
>   
> > No.  You have to physically shut down and start up again.  That's
> > the right semantics IMHO.
> >
> >     
> Reset is equivalent (or should be) to shut down and start up again.
>   

Not at all.  Reset can happen in a lot of different ways, some that 
there is really no way to detect (jumping right to BIOS vector).  From a 
hardware perspective, powering down a CPU and powering it on again 
behaves very differently than reset (consider the VT enablement MSRs).

> > > Second what if ROM size have changed (on destination it is
> > > smaller)?
> > >       
> > Then we're in trouble :-)
> >     
> Yeah, we are. May be relaying on file size is not good enough heuristic
> to determine ROM BAR size.
>   

Practically speaking, I don't think it's a huge problem to be honest.  
It's a very unlikely scenario.  We could make the rom size a qdev 
property which would allow a user to explicitly deal with this case.

> > But the fw_cfg rom loading doesn't seem handle migration :-/
> >
> >     
> Looks like it. We should send them over during migration too.
>   

We should just qemu_ram_alloc() that memory regardless of whether we 
every map it into the guest.  Since roms can be large, we want to send 
their contents over during the live part of migration.  If we use 
qemu_ram_alloc(), we get that for free.

Regards,

Anthony Liguori