{
unsigned int length = skb->len - ETH_HLEN;
- if (skb->protocol == htons(ETH_P_8021Q))
+ if (skb_vlan_tagged(skb))
length -= VLAN_HLEN;
+ /* Don't subtract for multiple VLAN tags. Most (all?) drivers allow
+ * (ETH_LEN + VLAN_HLEN) in addition to the mtu value, but almost none
+ * account for 802.1ad. e.g. is_skb_forwardable().
+ */
+
return length;
}