xen-netback: handle IPv6 TCP GSO packets from the guest

This patch adds a xenstore feature flag, festure-gso-tcpv6, to advertise
that netback can handle IPv6 TCP GSO packets. It creates SKB_GSO_TCPV6 skbs
if the frontend passes an extra segment with the new type
XEN_NETIF_GSO_TYPE_TCPV6 added to netif.h.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -1098,15 +1098,20 @@ static int xenvif_set_skb_gso(struct xenvif *vif,
 		return -EINVAL;
 	}
 
-	/* Currently only TCPv4 S.O. is supported. */
-	if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4) {
+	switch (gso->u.gso.type) {
+	case XEN_NETIF_GSO_TYPE_TCPV4:
+		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
+		break;
+	case XEN_NETIF_GSO_TYPE_TCPV6:
+		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
+		break;
+	default:
 		netdev_err(vif->dev, "Bad GSO type %d.\n", gso->u.gso.type);
 		xenvif_fatal_tx_err(vif);
 		return -EINVAL;
 	}
 
 	skb_shinfo(skb)->gso_size = gso->u.gso.size;
-	skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
 
 	/* Header must be checked, and gso_segs computed. */
 	skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;

drivers/net/xen-netback/xenbus.c

@@ -105,6 +105,13 @@ static int netback_probe(struct xenbus_device *dev,
 			goto abort_transaction;
 		}
 
+		err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv6",
+				    "%d", sg);
+		if (err) {
+			message = "writing feature-gso-tcpv6";
+			goto abort_transaction;
+		}
+
 		/* We support partial checksum setup for IPv6 packets */
 		err = xenbus_printf(xbt, dev->nodename,
 				    "feature-ipv6-csum-offload",

include/xen/interface/io/netif.h

@@ -57,6 +57,13 @@
  * offload on or off. If it is missing then the feature is assumed to be off.
  */
 
+/*
+ * "feature-gso-tcpv4" and "feature-gso-tcpv6" advertise the capability to
+ * handle large TCP packets (in IPv4 or IPv6 form respectively). Neither
+ * frontends nor backends are assumed to be capable unless the flags are
+ * present.
+ */
+
 /*
  * This is the 'wire' format for packets:
  *  Request 1: xen_netif_tx_request  -- XEN_NETTXF_* (any flags)
@@ -102,8 +109,9 @@ struct xen_netif_tx_request {
 #define _XEN_NETIF_EXTRA_FLAG_MORE	(0)
 #define  XEN_NETIF_EXTRA_FLAG_MORE	(1U<<_XEN_NETIF_EXTRA_FLAG_MORE)
 
-/* GSO types - only TCPv4 currently supported. */
+/* GSO types */
 #define XEN_NETIF_GSO_TYPE_TCPV4	(1)
+#define XEN_NETIF_GSO_TYPE_TCPV6	(2)
 
 /*
  * This structure needs to fit within both netif_tx_request and