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

["Andreas Färber" <afaerber@suse.de>]

Am 26.07.2013 15:09, schrieb Vincenzo Maffione:
> 2013/7/26 Andreas Färber <afaerber@suse.de>:
>> 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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