net: Add function for parsing the header length out of linear ethernet frames

[deliverable/linux.git] / net / ethernet / eth.c

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 5cebca134585862303114735fe64ceaf5e44c81f..33a140e1583449bcf2816bb91792e810f7c1734f 100644 (file)
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -145,6 +145,33 @@ int eth_rebuild_header(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(eth_rebuild_header);
 
+/**
+ * eth_get_headlen - determine the the length of header for an ethernet frame
+ * @data: pointer to start of frame
+ * @len: total length of frame
+ *
+ * Make a best effort attempt to pull the length for all of the headers for
+ * a given frame in a linear buffer.
+ */
+u32 eth_get_headlen(void *data, unsigned int len)
+{
+       const struct ethhdr *eth = (const struct ethhdr *)data;
+       struct flow_keys keys;
+
+       /* this should never happen, but better safe than sorry */
+       if (len < sizeof(*eth))
+               return len;
+
+       /* parse any remaining L2/L3 headers, check for L4 */
+       if (!__skb_flow_dissect(NULL, &keys, data,
+                               eth->h_proto, sizeof(*eth), len))
+               return max_t(u32, keys.thoff, sizeof(*eth));
+
+       /* parse for any L4 headers */
+       return min_t(u32, __skb_get_poff(NULL, data, &keys, len), len);
+}
+EXPORT_SYMBOL(eth_get_headlen);
+
 /**
  * eth_type_trans - determine the packet's protocol ID.
  * @skb: received socket data