Re: [Qemu-devel] [PATCH v7 0/9] Add limited support of VMware's hyper-call rpc

[Paolo Bonzini <pbonzini@redhat.com>]

On 17/06/2015 19:03, Don Slutz wrote:
> On 06/17/15 12:29, Michael S. Tsirkin wrote:
>> On Wed, Jun 17, 2015 at 06:17:19PM +0200, Paolo Bonzini wrote:
>>>
>>>
>>> On 17/06/2015 16:29, Michael S. Tsirkin wrote:
>>>> On Wed, Jun 17, 2015 at 04:27:13PM +0200, Paolo Bonzini wrote:
>>>>>
>>>>>
>>>>> On 17/06/2015 16:18, Michael S. Tsirkin wrote:
>>>>>>>> Yes, that's what was done for parallel and pcspk as well.  There's no
>>>>>>>> infrastructure to avoid it.
>>>>>>>>
>>>>>>>> Paolo
>>>>>> How do you mean? We have multiple ways to keep devices
>>>>>> compatible with old versions.
>>>>>> Set a new property to skip the extra stuff.
>>>>>
>>>>> Not if the device didn't have a vmstate at all, unfortunately.
>>>>
>>>> Skip creating the device completely for old machine types.
>>>
>>> Which device?  The vmstate is tied to the same device that has always
>>> been created.
>>
>> Just disable the new functionality. Make it behave in
>> a compatible way.
>>
>>>  we enable this thing by default (why do we?)
>>
>> Sigh. There is a very simple way to add a device in qemu: let user
>> request it with -device.  If one does this, one gets to maintain the
>> resulting mess without bothering with pc maintainers in any way.
>>
>> But of course, everyone implementing a new feature feels it's such a
>> great thing, and completel zero risk, it must be part of the default
>> machine. Guess what, one then gets to bother with versioning from day 0.
>>
>>>>>> this seems like a big deal ...
>>>>>
>>>>> The PC speaker device is also enabled by default.
>>>>
>>>> This is historical, isn't it?
>>>
>>> Yes, but it has broken 2.3->2.2 migration.
>>>
>>> Let's just stop fighting windmills.
>>>
>>> Paolo
>>
>> I don't see what you are saying. Suddenly guest visible
>> changes within a machine type are ok?
>>
>> So we have a bug, need to fix it, preferably before piling up
>> more features. The best way imho is for 2.4 to avoid
>> this device unless requested explicitly.
>>
> 
> My take on this is that Michael would like me to have a vmport_rpc=on
> option, just like vmport=on (which already exists).  With a default of off.

It wouldn't be enough, because dc->vmsd would be non-NULL anyway.

(But yes, that option would be a good thing anyway).

Paolo