Re: [Qemu-devel] [PATCH] Change virtio-console to PCI_CLASS_SERIAL_OTHER

[Anthony Liguori <aliguori@us.ibm.com>]

Paul Brook wrote:
>>>>   - the device model cannot change or the guest OS will get confused
>>>>         
>>> IMHO think the only sane response is "don't do that". Trying to support
>>> migration between different qemu versions just isn't worth the pain.
>>>       
>> It is very worth the pain.  I consider it a core requirement.
>>     
>
> We disagree then. You're effectively requiring bug-compatibility.
>   

You can take it to an extreme and require bug-compatibility, but I don't
think that's necessary.  I think there's room for being reasonable.

> This may be reasonable for a stable branch, but is not something I have any 
> interest in across different release cycles. IMHO major VM upgrades should be 
> considered the same as real hardware or firmware upgrades.
>   

I think major VM upgrades is something that can be considered
occasionally but every 6 months would be pretty painful to most users. 
I think we ought to make a best effort to maintain compatibility with
older versions as long as it's reasonable.

Regards,

Anthony Liguori

> Paul
>