net: core: move pop MPLS functionality from OvS to core helper

Open vSwitch provides code to pop an MPLS header to a packet. In
preparation for supporting this in TC, move the pop code to an skb helper
that can be reused.

Remove the, now unused, update_ethertype static function from OvS.
Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -3448,6 +3448,7 @@ int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci);
 int skb_vlan_pop(struct sk_buff *skb);
 int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
 int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto);
+int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto);
 struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
 			     gfp_t gfp);
 

net/core/skbuff.c

@@ -5489,6 +5489,48 @@ int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto)
 }
 EXPORT_SYMBOL_GPL(skb_mpls_push);
 
+/**
+ * skb_mpls_pop() - pop the outermost MPLS header
+ *
+ * @skb: buffer
+ * @next_proto: ethertype of header after popped MPLS header
+ *
+ * Expects skb->data at mac header.
+ *
+ * Returns 0 on success, -errno otherwise.
+ */
+int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto)
+{
+	int err;
+
+	if (unlikely(!eth_p_mpls(skb->protocol)))
+		return -EINVAL;
+
+	err = skb_ensure_writable(skb, skb->mac_len + MPLS_HLEN);
+	if (unlikely(err))
+		return err;
+
+	skb_postpull_rcsum(skb, mpls_hdr(skb), MPLS_HLEN);
+	memmove(skb_mac_header(skb) + MPLS_HLEN, skb_mac_header(skb),
+		skb->mac_len);
+
+	__skb_pull(skb, MPLS_HLEN);
+	skb_reset_mac_header(skb);
+	skb_set_network_header(skb, skb->mac_len);
+
+	if (skb->dev && skb->dev->type == ARPHRD_ETHER) {
+		struct ethhdr *hdr;
+
+		/* use mpls_hdr() to get ethertype to account for VLANs. */
+		hdr = (struct ethhdr *)((void *)mpls_hdr(skb) - ETH_HLEN);
+		skb_mod_eth_type(skb, hdr, next_proto);
+	}
+	skb->protocol = next_proto;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(skb_mpls_pop);
+
 /**
  * alloc_skb_with_frags - allocate skb with page frags
  *

net/openvswitch/actions.c

@@ -160,18 +160,6 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			      struct sw_flow_key *key,
 			      const struct nlattr *attr, int len);
 
-static void update_ethertype(struct sk_buff *skb, struct ethhdr *hdr,
-			     __be16 ethertype)
-{
-	if (skb->ip_summed == CHECKSUM_COMPLETE) {
-		__be16 diff[] = { ~(hdr->h_proto), ethertype };
-
-		skb->csum = csum_partial((char *)diff, sizeof(diff), skb->csum);
-	}
-
-	hdr->h_proto = ethertype;
-}
-
 static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
 		     const struct ovs_action_push_mpls *mpls)
 {
@@ -190,31 +178,10 @@ static int pop_mpls(struct sk_buff *skb, struct sw_flow_key *key,
 {
 	int err;
 
-	err = skb_ensure_writable(skb, skb->mac_len + MPLS_HLEN);
-	if (unlikely(err))
+	err = skb_mpls_pop(skb, ethertype);
+	if (err)
 		return err;
 
-	skb_postpull_rcsum(skb, mpls_hdr(skb), MPLS_HLEN);
-
-	memmove(skb_mac_header(skb) + MPLS_HLEN, skb_mac_header(skb),
-		skb->mac_len);
-
-	__skb_pull(skb, MPLS_HLEN);
-	skb_reset_mac_header(skb);
-	skb_set_network_header(skb, skb->mac_len);
-
-	if (ovs_key_mac_proto(key) == MAC_PROTO_ETHERNET) {
-		struct ethhdr *hdr;
-
-		/* mpls_hdr() is used to locate the ethertype field correctly in the
-		 * presence of VLAN tags.
-		 */
-		hdr = (struct ethhdr *)((void *)mpls_hdr(skb) - ETH_HLEN);
-		update_ethertype(skb, hdr, ethertype);
-	}
-	if (eth_p_mpls(skb->protocol))
-		skb->protocol = ethertype;
-
 	invalidate_flow_key(key);
 	return 0;
 }