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

[Blue Swirl <blauwirbel@gmail.com>]

On Sun, Dec 20, 2009 at 3:52 PM, Gleb Natapov <gleb@redhat.com> wrote:
> On Sun, Dec 20, 2009 at 09:39:38AM -0600, Anthony Liguori wrote:
>> Gleb Natapov wrote:
>> >>More importantly though, what's the use-case here?
>> >>
>> >Use-case for what? This just what need to be done for correct HW
>> >emulation.
>>
>> Live migration is transparent to the guest.  The fact that firmware
>> can upgrade itself without the guest doing anything is not something
>> that really has a real world equivalent.
>>
>> Even if it did, whether that automatic upgrade happens after a
>> reboot vs. a hard power cycle is irrelevant.  The guest has no
>> knowledge of the fact that the automatic firmware upgrade happened
>> so if it gets delayed indefinitely, it doesn't matter.
>>
>> It's not a matter of correctness IMHO.
>>
> Ah now I see what you mean. New FW has to be used after reboot because old
> one may not be able to init HW any longer. Suppose some bug in cirrus
> emulation has being fixed and old vga bios should be accommodated to
> those changes, if old vga bios will run after reset video output may not
> work. Thinking about it we'll have the same problem if migration happens
> during vga bios loading, but this is MUCH less likely to happen.
>
>> I can understand an argument for predictability wrt wanted to be
>> able to guarantee that after the first reboot during a live
>> migration, you'll get the new firmware.  I'm not sure that's less
>> predictable then hard shutdown/start-up and I'm not sure I can
>> really make an argument for one way vs. the other.
>>
> system_reset _is_ hard shutdown/start-up. If it is not it is a bug, we
> just arguing if the same applies for the case that migration was done
> between boot and reset.

Some devices are careful enough to implement warm reset using a flag,
see for example hw/sun4u.c. If you want more precision, you could
introduce for example system_off_on with the memory clearing behavior
you want.