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

[Michael S. Tsirkin]

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.

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