Re: [Qemu-devel] [Qemu-ppc] [PATCH] target-ppc: Add @cpu_dt_id into migration stream

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 04/11/2014 12:49 AM, Peter Maydell wrote:
> On 10 April 2014 15:35, Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>> Then what is the purpose of many, many VMSTATE_.*_EQUAL?
> 
> Often it's backwards compatibility with a previous vmstate
> or save/load function set which incorrectly sent data it didn't
> need to.
> 
>> And I do not want to send configuration by the proposed patch, I want to
>> make sure that the new guest is able to continue. Why exactly is this bad?
> 
> It's not bad, but as several people have now pointed out to you,
> you're trying to fix a tiny tiny corner of the real, larger
> problem, in a way which isn't going to generalise to actually
> fixing the larger problem. So if we took your change then
> (a) we still wouldn't be able to support detection of migration
> between two systems with mismatched configuration, so it doesn't
> really achieve anything
> (b) if we ever did manage to fix that we'd have to remove your
> change (because that bit of config checking would now be handled
> via whatever generic mechanism we implemented), except we probably
> couldn't remove it since that would break migration version
> compatibility, so we'd end up with a wart we have to carry
> around forever

Ok, understood. Thanks.


ps. yeah, I do not often see the bigger picture, I know :(
-- 
Alexey