net: core: add MPLS update core helper and use in OvS

Open vSwitch allows the updating of an existing MPLS header on a packet.
In preparation for supporting similar functionality in TC, move this to a
common skb helper function.

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>

1 files changed, 33 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8c00be4d8919..93443a01ab39 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5532,6 +5532,39 @@ int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto)
 EXPORT_SYMBOL_GPL(skb_mpls_pop);
 
 /**
+ * skb_mpls_update_lse() - modify outermost MPLS header and update csum
+ *
+ * @skb: buffer
+ * @mpls_lse: new MPLS label stack entry to update to
+ *
+ * Expects skb->data at mac header.
+ *
+ * Returns 0 on success, -errno otherwise.
+ */
+int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse)
+{
+	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;
+
+	if (skb->ip_summed == CHECKSUM_COMPLETE) {
+		__be32 diff[] = { ~mpls_hdr(skb)->label_stack_entry, mpls_lse };
+
+		skb->csum = csum_partial((char *)diff, sizeof(diff), skb->csum);
+	}
+
+	mpls_hdr(skb)->label_stack_entry = mpls_lse;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(skb_mpls_update_lse);
+
+/**
  * alloc_skb_with_frags - allocate skb with page frags
  *
  * @header_len: size of linear part