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

[Jason Wang]

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? In this case, you
won't detect any kick if you don't send the rarp first.