xen-netback: retire guest rx side prefix GSO feature

As far as I am aware only very old Windows network frontends make use of
this style of passing GSO packets from backend to frontend. These
frontends can easily be replaced by the freely available Xen Project
Windows PV network frontend, which uses the 'default' mechanism for
passing GSO packets, which is also used by all Linux frontends.

NOTE: Removal of this feature will not cause breakage in old Windows
      frontends. They simply will no longer receive GSO packets - the
      packets instead being fragmented in the backend.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -260,7 +260,6 @@ struct xenvif {
 
 	/* Frontend feature information. */
 	int gso_mask;
-	int gso_prefix_mask;
 
 	u8 can_sg:1;
 	u8 ip_csum:1;

drivers/net/xen-netback/interface.c

@@ -319,9 +319,9 @@ static netdev_features_t xenvif_fix_features(struct net_device *dev,
 
 	if (!vif->can_sg)
 		features &= ~NETIF_F_SG;
-	if (~(vif->gso_mask | vif->gso_prefix_mask) & GSO_BIT(TCPV4))
+	if (~(vif->gso_mask) & GSO_BIT(TCPV4))
 		features &= ~NETIF_F_TSO;
-	if (~(vif->gso_mask | vif->gso_prefix_mask) & GSO_BIT(TCPV6))
+	if (~(vif->gso_mask) & GSO_BIT(TCPV6))
 		features &= ~NETIF_F_TSO6;
 	if (!vif->ip_csum)
 		features &= ~NETIF_F_IP_CSUM;

drivers/net/xen-netback/rx.c

@@ -347,16 +347,6 @@ static int xenvif_gop_skb(struct sk_buff *skb,
 			gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
 	}
 
-	/* Set up a GSO prefix descriptor, if necessary */
-	if ((1 << gso_type) & vif->gso_prefix_mask) {
-		RING_COPY_REQUEST(&queue->rx, queue->rx.req_cons++, &req);
-		meta = npo->meta + npo->meta_prod++;
-		meta->gso_type = gso_type;
-		meta->gso_size = skb_shinfo(skb)->gso_size;
-		meta->size = 0;
-		meta->id = req.id;
-	}
-
 	RING_COPY_REQUEST(&queue->rx, queue->rx.req_cons++, &req);
 	meta = npo->meta + npo->meta_prod++;
 
@@ -511,22 +501,6 @@ static void xenvif_rx_action(struct xenvif_queue *queue)
 	while ((skb = __skb_dequeue(&rxq)) != NULL) {
 		struct xen_netif_extra_info *extra = NULL;
 
-		if ((1 << queue->meta[npo.meta_cons].gso_type) &
-		    vif->gso_prefix_mask) {
-			resp = RING_GET_RESPONSE(&queue->rx,
-						 queue->rx.rsp_prod_pvt++);
-
-			resp->flags = XEN_NETRXF_gso_prefix |
-				      XEN_NETRXF_more_data;
-
-			resp->offset = queue->meta[npo.meta_cons].gso_size;
-			resp->id = queue->meta[npo.meta_cons].id;
-			resp->status = XENVIF_RX_CB(skb)->meta_slots_used;
-
-			npo.meta_cons++;
-			XENVIF_RX_CB(skb)->meta_slots_used--;
-		}
-
 		queue->stats.tx_bytes += skb->len;
 		queue->stats.tx_packets++;
 

drivers/net/xen-netback/xenbus.c

@@ -1135,40 +1135,19 @@ static int read_xenbus_vif_flags(struct backend_info *be)
 	vif->can_sg = !!val;
 
 	vif->gso_mask = 0;
-	vif->gso_prefix_mask = 0;
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4",
 			 "%d", &val) < 0)
 		val = 0;
 	if (val)
 		vif->gso_mask |= GSO_BIT(TCPV4);
 
-	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4-prefix",
-			 "%d", &val) < 0)
-		val = 0;
-	if (val)
-		vif->gso_prefix_mask |= GSO_BIT(TCPV4);
-
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv6",
 			 "%d", &val) < 0)
 		val = 0;
 	if (val)
 		vif->gso_mask |= GSO_BIT(TCPV6);
 
-	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv6-prefix",
-			 "%d", &val) < 0)
-		val = 0;
-	if (val)
-		vif->gso_prefix_mask |= GSO_BIT(TCPV6);
-
-	if (vif->gso_mask & vif->gso_prefix_mask) {
-		xenbus_dev_fatal(dev, err,
-				 "%s: gso and gso prefix flags are not "
-				 "mutually exclusive",
-				 dev->otherend);
-		return -EOPNOTSUPP;
-	}
-
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-no-csum-offload",
 			 "%d", &val) < 0)
 		val = 0;