Re: [Qemu-devel] [PATCH] Migration compatibility for serial

[Paolo Bonzini]

On 17/06/2015 12:13, Michael S. Tsirkin wrote:
> On Wed, Jun 17, 2015 at 10:11:48AM +0200, Paolo Bonzini wrote:
>>
>>
>> On 17/06/2015 09:52, Michael S. Tsirkin wrote:
>>>> No, please.  Upstream QEMU doesn't want to get into judgement about when
>>>> migration quality might be "good enough" that you can drop subsections.
>>>>  It's one thing to perfect the .needed functions to make the appearance
>>>> of subsections as unlikely as possible, but adding flags is not
>>>> something we've done so far---and not something at least *I* want to do.
>>>
>>> Not like this, sure.  But e.g. patches that force specific fields to
>>> behave in a way consistent with QEMU 2.2, with appropriate
>>> doducmentation would be ok I think.
>>
>> That's not what 2.2 means in "pc-i440fx-2.2".  It means "same hardware
>> as 2.2", not "bug-compatible with 2.2".
>>
>> Refining the .needed functions (e.g. see commit bfa7362889) is just
>> that: describing when a subsection is needed.  Forcing specific fields
>> to behave in a way consistent with QEMU 2.2 is bug compatibility.
> 
> We do bug-compatible if it's not a big pain, too.

Where, in the specific case of migration?

Like Juan, I see where you're coming from.  But it's a slippery slope,
and upstream chose not to go down it.

Paolo