On Mon, Aug 29, 2022 at 11:44:09AM +0200, Wojciech Drewek wrote:

Allow to dissect L2TPv3 specific field which is:
- session ID (32 bits)

L2TPv3 might be transported over IP or over UDP,
this ipmplementation is only about L2TPv3 over IP.
IP protocold carries L2TPv3 when ip_proto is

s/protocold/protocol/

+static void __skb_flow_dissect_l2tpv3(const struct sk_buff *skb,
+				      struct flow_dissector *flow_dissector,
+				      void *target_container, const void *data,
+				      int nhoff, int hlen)
+{
+	struct flow_dissector_key_l2tpv3 *key_l2tpv3;
+	struct {
+		__be32 session_id;
+	} *hdr, _hdr;
+
+	hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr);
+	if (!hdr)
+		return;
+
+	if (!dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_L2TPV3))
+		return;

I'd find it more logical to test !dissector_uses_key() first, then call
__skb_header_pointer(). But that probably just a personnal preference.

In any case the code looks good to me.

Acked-by: Guillaume Nault <redacted>