ip6gre: Add support for basic offloads offloads excluding GSO

This patch adds support for the basic offloads we support on most devices.
Specifically with this patch set we can support checksum offload, basic
scatter-gather, and highdma.
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -598,6 +598,18 @@ static void init_tel_txopt(struct ipv6_tel_txoption *opt, __u8 encap_limit)
 	opt->ops.opt_nflen = 8;
 }
 
+static __sum16 gre6_checksum(struct sk_buff *skb)
+{
+	__wsum csum;
+
+	if (skb->ip_summed == CHECKSUM_PARTIAL)
+		csum = lco_csum(skb);
+	else
+		csum = skb_checksum(skb, sizeof(struct ipv6hdr),
+				    skb->len - sizeof(struct ipv6hdr), 0);
+	return csum_fold(csum);
+}
+
 static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
 			 struct net_device *dev,
 			 __u8 dsfield,
@@ -750,8 +762,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
 		}
 		if (tunnel->parms.o_flags&GRE_CSUM) {
 			*ptr = 0;
-			*(__sum16 *)ptr = ip_compute_csum((void *)(ipv6h+1),
-				skb->len - sizeof(struct ipv6hdr));
+			*(__sum16 *)ptr = gre6_checksum(skb);
 		}
 	}
 
@@ -1507,6 +1518,11 @@ static const struct net_device_ops ip6gre_tap_netdev_ops = {
 	.ndo_get_iflink = ip6_tnl_get_iflink,
 };
 
+#define GRE6_FEATURES (NETIF_F_SG |		\
+		       NETIF_F_FRAGLIST |	\
+		       NETIF_F_HIGHDMA |		\
+		       NETIF_F_HW_CSUM)
+
 static void ip6gre_tap_setup(struct net_device *dev)
 {
 
@@ -1540,6 +1556,9 @@ static int ip6gre_newlink(struct net *src_net, struct net_device *dev,
 	nt->net = dev_net(dev);
 	ip6gre_tnl_link_config(nt, !tb[IFLA_MTU]);
 
+	dev->features		|= GRE6_FEATURES;
+	dev->hw_features	|= GRE6_FEATURES;
+
 	/* Can use a lockless transmit, unless we generate output sequences */
 	if (!(nt->parms.o_flags & GRE_SEQ))
 		dev->features |= NETIF_F_LLTX;