Re: [Qemu-devel] [RFC] vhost-user: introduce F_NEED_ALL_IOTLB protocol feature

[Jason Wang <jasowang@redhat.com>]

On 2018年04月12日 11:37, Michael S. Tsirkin wrote:
>>>>> Yeah, we are still using the existing IOTLB update messages
>>>>> to send the IOTLB messages to backend. The only difference
>>>>> is that, QEMU won't wait for the queries before sending the
>>>>> IOTLB update messages.
>>>> Yes, my question is not very clear. I mean why must need a new feature bit?
>>>> It looks to me qemu code can work without this.
>>>>
>>>> Thanks
>>> Generally we avoid adding new messages without a protocol feature bit.
>>> While careful analysis might sometimes prove it's not a strict
>>> requirement, it's just overall a clean and robust approach.
>>>
>> Right but the looks like the patch does not introduce any new type of
>> messages.
>>
>> Thanks
> In this case remote needs to know that it will send these messages.
>
> -- MST

Ok, if some backend does not expect qemu will send without any query 
from itself, I agree we need a new bit.

But it looks more like a workaround for buggy backend, at least vhost 
kernel does not need to know about this.

Thanks