flow_dissector: dissect tunnel info outside __skb_flow_dissect()

Move dissection of tunnel info to outside of the main flow dissection
function, __skb_flow_dissect(). The sole user of this feature, the flower
classifier, is updated to call tunnel info dissection directly, using
skb_flow_dissect_tunnel_info().

This results in a slightly less complex implementation of
__skb_flow_dissect(), in particular removing logic from that call path
which is not used by the majority of users. The expense of this is borne by
the flower classifier which now has to make an extra call for tunnel info
dissection.

This patch should not result in any behavioural change.
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1211,6 +1211,11 @@ static inline bool skb_flow_dissect_flow_keys_buf(struct flow_keys *flow,
 				  data, proto, nhoff, hlen, flags);
 }
 
+void
+skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
+			     struct flow_dissector *flow_dissector,
+			     void *target_container);
+
 static inline __u32 skb_get_hash(struct sk_buff *skb)
 {
 	if (!skb->l4_hash && !skb->sw_hash)

net/core/flow_dissector.c

@@ -133,8 +133,8 @@ skb_flow_dissect_set_enc_addr_type(enum flow_dissector_key_id type,
 	ctrl->addr_type = type;
 }
 
-static void
-__skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
+void
+skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
 			     struct flow_dissector *flow_dissector,
 			     void *target_container)
 {
@@ -212,6 +212,7 @@ __skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
 		tp->dst = key->tp_dst;
 	}
 }
+EXPORT_SYMBOL(skb_flow_dissect_tunnel_info);
 
 static enum flow_dissect_ret
 __skb_flow_dissect_mpls(const struct sk_buff *skb,
@@ -576,9 +577,6 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 					      FLOW_DISSECTOR_KEY_BASIC,
 					      target_container);
 
-	__skb_flow_dissect_tunnel_info(skb, flow_dissector,
-				       target_container);
-
 	if (dissector_uses_key(flow_dissector,
 			       FLOW_DISSECTOR_KEY_ETH_ADDRS)) {
 		struct ethhdr *eth = eth_hdr(skb);

net/sched/cls_flower.c

@@ -166,6 +166,7 @@ static int fl_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 	 * so do it rather here.
 	 */
 	skb_key.basic.n_proto = skb->protocol;
+	skb_flow_dissect_tunnel_info(skb, &head->dissector, &skb_key);
 	skb_flow_dissect(skb, &head->dissector, &skb_key, 0);
 
 	fl_set_masked_key(&skb_mkey, &skb_key, &head->mask);