[UDP]: Introduce UDP encapsulation type for L2TP

This patch adds a new UDP_ENCAP_L2TPINUDP encapsulation type for UDP
sockets. When a UDP socket's encap_type is UDP_ENCAP_L2TPINUDP, the
skb is delivered to a function pointed to by the udp_sock's
encap_rcv funcptr. If the skb isn't wanted by L2TP, it returns >0, which
causes it to be passed through to UDP.

Include padding to put the new encap_rcv field on a 4-byte boundary.

Previously, the only user of UDP encap sockets was ESP, so when
CONFIG_XFRM was not defined, some of the encap code was compiled
out. This patch changes that. As a result, udp_encap_rcv() will
now do a little more work when CONFIG_XFRM is not defined.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 6de445c31a64..8ec703f462da 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -42,6 +42,7 @@ static inline struct udphdr *udp_hdr(const struct sk_buff *skb)
 /* UDP encapsulation types */
 #define UDP_ENCAP_ESPINUDP_NON_IKE      1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
 #define UDP_ENCAP_ESPINUDP      2 /* draft-ietf-ipsec-udp-encaps-06 */
+#define UDP_ENCAP_L2TPINUDP     3 /* rfc2661 */
 
 #ifdef __KERNEL__
 #include <linux/types.h>
@@ -70,6 +71,11 @@ struct udp_sock {
 #define UDPLITE_SEND_CC  0x2            /* set via udplite setsockopt         */
 #define UDPLITE_RECV_CC  0x4            /* set via udplite setsocktopt        */
         __u8             pcflag;        /* marks socket as UDP-Lite if > 0    */
+        __u8             unused[3];
+        /*
+         * For encapsulation sockets.
+         */
+        int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
 };
 
 static inline struct udp_sock *udp_sk(const struct sock *sk)