net: Add priority to packet_offload objects.

When we scan a packet for GRO processing, we want to see the most
common packet types in the front of the offload_base list.

So add a priority field so we can handle this properly.

IPv4/IPv6 get the highest priority with the implicit zero priority
field.

Next comes ethernet with a priority of 10, and then we have the MPLS
types with a priority of 15.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Suggested-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: davem330

include/linux/netdevice.h

@@ -1997,6 +1997,7 @@ struct offload_callbacks {
 
 struct packet_offload {
 	__be16			 type;	/* This is really htons(ether_type). */
+	u16			 priority;
 	struct offload_callbacks callbacks;
 	struct list_head	 list;
 };

net/core/dev.c

@@ -469,10 +469,14 @@ EXPORT_SYMBOL(dev_remove_pack);
  */
 void dev_add_offload(struct packet_offload *po)
 {
-	struct list_head *head = &offload_base;
+	struct packet_offload *elem;
 
 	spin_lock(&offload_lock);
-	list_add_rcu(&po->list, head);
+	list_for_each_entry(elem, &offload_base, list) {
+		if (po->priority < elem->priority)
+			break;
+	}
+	list_add_rcu(&po->list, elem->list.prev);
 	spin_unlock(&offload_lock);
 }
 EXPORT_SYMBOL(dev_add_offload);

net/ethernet/eth.c

@@ -470,6 +470,7 @@ EXPORT_SYMBOL(eth_gro_complete);
 
 static struct packet_offload eth_packet_offload __read_mostly = {
 	.type = cpu_to_be16(ETH_P_TEB),
+	.priority = 10,
 	.callbacks = {
 		.gro_receive = eth_gro_receive,
 		.gro_complete = eth_gro_complete,

net/mpls/mpls_gso.c

@@ -62,13 +62,15 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
 
 static struct packet_offload mpls_mc_offload __read_mostly = {
 	.type = cpu_to_be16(ETH_P_MPLS_MC),
+	.priority = 15,
 	.callbacks = {
 		.gso_segment    =	mpls_gso_segment,
 	},
 };
 
 static struct packet_offload mpls_uc_offload __read_mostly = {
 	.type = cpu_to_be16(ETH_P_MPLS_UC),
+	.priority = 15,
 	.callbacks = {
 		.gso_segment    =	mpls_gso_segment,
 	},