net: Add function for parsing the header length out of linear ethernet frames
This patch updates some of the flow_dissector api so that it can be used to
parse the length of ethernet buffers stored in fragments. Most of the
changes needed were to __skb_get_poff as it needed to be updated to support
sending a linear buffer instead of a skb.
I have split __skb_get_poff into two functions, the first is skb_get_poff
and it retains the functionality of the original __skb_get_poff. The other
function is __skb_get_poff which now works much like __skb_flow_dissect in
relation to skb_flow_dissect in that it provides the same functionality but
works with just a data buffer and hlen instead of needing an skb.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 5cebca1..33a140e 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -146,6 +146,33 @@
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
* @dev: receiving network device