Re: [Qemu-devel] [PATCH v3 2/2] vhost user: Add RARP injection for legacy guest

[Jason Wang <jasowang@redhat.com>]

On 06/12/2015 10:28 PM, Michael S. Tsirkin wrote:
> On Fri, Jun 12, 2015 at 03:55:33PM +0800, Jason Wang wrote:
>>
>> On 06/11/2015 08:13 PM, Michael S. Tsirkin wrote:
>>> On Thu, Jun 11, 2015 at 02:10:48PM +0200, Thibaut Collet wrote:
>>>> I am not sure to understand your remark:
>>>>
>>>>> It needs to be sent when backend is activated by guest kick
>>>>> (in case of virtio 1, it's possible to use DRIVER_OK for this).
>>>>> This does not happen when VM still runs on source.
>>>> Could you confirm rarp can be sent by backend when the 
>>>> VHOST_USER_SET_VRING_KICK message is received by the backend ?
>>> No - the time to send pakets is when you start processing
>>> the rings.
>>>
>>> And the time to do that is when you detect a kick on
>>> an eventfd, not when said fd is set.
>>>
>> Probably not. What if guest is only doing receiving?
> Clarification: the kick can be on any VQs.
> In your example, guest kicks after adding receive buffers.

Yes, but refill only happens on we are lacking of receive buffers. It is
not guaranteed to happen just after migration, we may have still have
enough rx buffers for device to receive.
>
>> In this case, you
>> won't detect any kick if you don't send the rarp first.