Re: [Qemu-devel] [PATCH v2] e1000: add interrupt mitigation support

[Vincenzo Maffione]

That's very clear!

Thanks,
  Vincenzo

2013/7/26 Andreas Färber <address@hidden>:
> Am 26.07.2013 15:09, schrieb Vincenzo Maffione:
>> 2013/7/26 Andreas Färber <address@hidden>:
>>> Am 26.07.2013 12:14, schrieb Vincenzo Maffione:
>>>>   I tried to support cross-version migration using version_id and
>>>> VMState subsections.
>>>
>>> The point of using a subsection is to avoid incrementing version_id AFAIU.
>>
>> Consider a migration from an older QEMU version to a newer one.
>> AFAIU, the e1000_post_load() callback is passed "1" or "2" into the
>> "version_id" parameter (i.e. the e1000 version of the older QEMU).
>> If that is correct, in this scenario I have to zero-init the new
>> fields I implemented, otherwise they would stay uninitialized.
>
> The whole state struct is always zero-initialized as part of
> object_new()/qdev_create(). So only non-zero fields need to be
> initialized, and I assume that a zero flag will indicate no mitigation
> feature.
>
>> If I don't increment version_id to 3, how can I understand when we are
>> in this scenario?
>>
>> Or maybe I should assume that (in the same scenario) the new version
>> QEMU instance MUST have been launched with the mitigation disabled? If
>> I assume this it seems to me that incrementing version_id to 3 is not
>> necessary.
>
> You can assume that you have equivalent command lines on both source and
> destination. -M pc-i440fx-1.5 and -M pc-q35-1.5 would simply never
> receive your subsection. I'm sure Stefan can explain in more detail.
>
> Regards,
> Andreas
>
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-- 
Vincenzo Maffione