virtio-net: enable tap offload if guest supports it

We query the guest's feature set to see if it supports offload and,
if so, we enable those features on the tap interface.
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/virtio-net.c

@@ -152,6 +152,11 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev)
         features |= (1 << VIRTIO_NET_F_HOST_TSO4);
         features |= (1 << VIRTIO_NET_F_HOST_TSO6);
         features |= (1 << VIRTIO_NET_F_HOST_ECN);
+
+        features |= (1 << VIRTIO_NET_F_GUEST_CSUM);
+        features |= (1 << VIRTIO_NET_F_GUEST_TSO4);
+        features |= (1 << VIRTIO_NET_F_GUEST_TSO6);
+        features |= (1 << VIRTIO_NET_F_GUEST_ECN);
     }
 
     return features;
@@ -177,6 +182,14 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)
     VirtIONet *n = to_virtio_net(vdev);
 
     n->mergeable_rx_bufs = !!(features & (1 << VIRTIO_NET_F_MRG_RXBUF));
+
+    if (n->has_vnet_hdr) {
+        tap_set_offload(n->vc->peer,
+                        (features >> VIRTIO_NET_F_GUEST_CSUM) & 1,
+                        (features >> VIRTIO_NET_F_GUEST_TSO4) & 1,
+                        (features >> VIRTIO_NET_F_GUEST_TSO6) & 1,
+                        (features >> VIRTIO_NET_F_GUEST_ECN)  & 1);
+    }
 }
 
 static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd,
@@ -702,6 +715,11 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
 
         if (n->has_vnet_hdr) {
             tap_using_vnet_hdr(n->vc->peer, 1);
+            tap_set_offload(n->vc->peer,
+                            (n->vdev.features >> VIRTIO_NET_F_GUEST_CSUM) & 1,
+                            (n->vdev.features >> VIRTIO_NET_F_GUEST_TSO4) & 1,
+                            (n->vdev.features >> VIRTIO_NET_F_GUEST_TSO6) & 1,
+                            (n->vdev.features >> VIRTIO_NET_F_GUEST_ECN)  & 1);
         }
     }