[dpdk-dev] [PATCH v2 5/6] vhost: claim that we support GUEST_ANNOUNCE feature

[Peter Xu]

On Thu, Dec 17, 2015 at 11:12:00AM +0800, Yuanhan Liu wrote:
> It's actually a feature already enabled in Linux kernel. What we need to
> do is simply to claim that we support such feature, and nothing else.
> 
> With that, the guest will send GARP messages after live migration.
> 
> Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com>
> ---
>  lib/librte_vhost/virtio-net.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/librte_vhost/virtio-net.c b/lib/librte_vhost/virtio-net.c
> index 03044f6..0ba5045 100644
> --- a/lib/librte_vhost/virtio-net.c
> +++ b/lib/librte_vhost/virtio-net.c
> @@ -74,6 +74,7 @@ static struct virtio_net_config_ll *ll_root;
>  #define VHOST_SUPPORTED_FEATURES ((1ULL << VIRTIO_NET_F_MRG_RXBUF) | \
>  				(1ULL << VIRTIO_NET_F_CTRL_VQ) | \
>  				(1ULL << VIRTIO_NET_F_CTRL_RX) | \
> +				(1ULL << VIRTIO_NET_F_GUEST_ANNOUNCE) | \

Do we really need this? I can understand when guest declare with
this VIRTIO_NET_F_GUEST_ANNOUNCE flag. With that, guest itself will
handle the announcement after migration. However, how could I
understand if it's declared by a vhost-user backend? What does it
mean?

In vhost-user.txt (in QEMU repo docs/specs/), the only place that
mentioned this is SEND_RARP:

 * VHOST_USER_SEND_RARP

      Id: 19
      Equivalent ioctl: N/A
      Master payload: u64

      Ask vhost user backend to broadcast a fake RARP to notify the migration
      is terminated for guest that does not support GUEST_ANNOUNCE.
	  ...

Here, it mention the GUEST_ANNOUNCE since when guest support this,
we do not need to send SEND_RARP to vhost-user backend again. It
never explain what does it mean when vhost-user declaring to have
this flag...

Thanks.
Peter

>  				(VHOST_SUPPORTS_MQ)            | \
>  				(1ULL << VIRTIO_F_VERSION_1)   | \
>  				(1ULL << VHOST_F_LOG_ALL)      | \
> -- 
> 1.9.0
>