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

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

@@ -3447,6 +3447,7 @@ int skb_ensure_writable(struct sk_buff *skb, int write_len);
 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);
 struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
 			     gfp_t gfp);
 

net/core/skbuff.c

@@ -66,6 +66,7 @@
 #include <net/checksum.h>
 #include <net/ip6_checksum.h>
 #include <net/xfrm.h>
+#include <net/mpls.h>
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
@@ -5425,6 +5426,69 @@ int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 }
 EXPORT_SYMBOL(skb_vlan_push);
 
+/* Update the ethertype of hdr and the skb csum value if required. */
+static void skb_mod_eth_type(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;
+}
+
+/**
+ * skb_mpls_push() - push a new MPLS header after the mac header
+ *
+ * @skb: buffer
+ * @mpls_lse: MPLS label stack entry to push
+ * @mpls_proto: ethertype of the new MPLS header (expects 0x8847 or 0x8848)
+ *
+ * Expects skb->data at mac header.
+ *
+ * Returns 0 on success, -errno otherwise.
+ */
+int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto)
+{
+	struct mpls_shim_hdr *lse;
+	int err;
+
+	if (unlikely(!eth_p_mpls(mpls_proto)))
+		return -EINVAL;
+
+	/* Networking stack does not allow simultaneous Tunnel and MPLS GSO. */
+	if (skb->encapsulation)
+		return -EINVAL;
+
+	err = skb_cow_head(skb, MPLS_HLEN);
+	if (unlikely(err))
+		return err;
+
+	if (!skb->inner_protocol) {
+		skb_set_inner_network_header(skb, skb->mac_len);
+		skb_set_inner_protocol(skb, skb->protocol);
+	}
+
+	skb_push(skb, MPLS_HLEN);
+	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
+		skb->mac_len);
+	skb_reset_mac_header(skb);
+	skb_set_network_header(skb, skb->mac_len);
+
+	lse = mpls_hdr(skb);
+	lse->label_stack_entry = mpls_lse;
+	skb_postpush_rcsum(skb, lse, MPLS_HLEN);
+
+	if (skb->dev && skb->dev->type == ARPHRD_ETHER)
+		skb_mod_eth_type(skb, eth_hdr(skb), mpls_proto);
+	skb->protocol = mpls_proto;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(skb_mpls_push);
+
 /**
  * alloc_skb_with_frags - allocate skb with page frags
  *

net/openvswitch/actions.c

@@ -175,34 +175,11 @@ static void update_ethertype(struct sk_buff *skb, struct ethhdr *hdr,
 static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
 		     const struct ovs_action_push_mpls *mpls)
 {
-	struct mpls_shim_hdr *new_mpls_lse;
-
-	/* Networking stack do not allow simultaneous Tunnel and MPLS GSO. */
-	if (skb->encapsulation)
-		return -ENOTSUPP;
-
-	if (skb_cow_head(skb, MPLS_HLEN) < 0)
-		return -ENOMEM;
-
-	if (!skb->inner_protocol) {
-		skb_set_inner_network_header(skb, skb->mac_len);
-		skb_set_inner_protocol(skb, skb->protocol);
-	}
-
-	skb_push(skb, MPLS_HLEN);
-	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
-		skb->mac_len);
-	skb_reset_mac_header(skb);
-	skb_set_network_header(skb, skb->mac_len);
-
-	new_mpls_lse = mpls_hdr(skb);
-	new_mpls_lse->label_stack_entry = mpls->mpls_lse;
-
-	skb_postpush_rcsum(skb, new_mpls_lse, MPLS_HLEN);
+	int err;
 
-	if (ovs_key_mac_proto(key) == MAC_PROTO_ETHERNET)
-		update_ethertype(skb, eth_hdr(skb), mpls->mpls_ethertype);
-	skb->protocol = mpls->mpls_ethertype;
+	err = skb_mpls_push(skb, mpls->mpls_lse, mpls->mpls_ethertype);
+	if (err)
+		return err;
 
 	invalidate_flow_key(key);
 	return 0;