#include <linux/version.h>

#if LINUX_VERSION_CODE < KERNEL_VERSION(3,18,0)

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/socket.h>
#include <linux/udp.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <net/ip_tunnels.h>
#include <net/udp.h>
#include <net/udp_tunnel.h>
#include <net/net_namespace.h>

int udp_sock_create(struct net *net, struct udp_port_cfg *cfg,
		    struct socket **sockp)
{
	int err;
	struct socket *sock = NULL;

#if IS_ENABLED(CONFIG_IPV6)
	if (cfg->family == AF_INET6) {
		struct sockaddr_in6 udp6_addr;

		err = sock_create_kern(AF_INET6, SOCK_DGRAM, 0, &sock);
		if (err < 0)
			goto error;

		sk_change_net(sock->sk, net);

		udp6_addr.sin6_family = AF_INET6;
		memcpy(&udp6_addr.sin6_addr, &cfg->local_ip6,
		       sizeof(udp6_addr.sin6_addr));
		udp6_addr.sin6_port = cfg->local_udp_port;
		err = kernel_bind(sock, (struct sockaddr *)&udp6_addr,
				  sizeof(udp6_addr));
		if (err < 0)
			goto error;

		if (cfg->peer_udp_port) {
			udp6_addr.sin6_family = AF_INET6;
			memcpy(&udp6_addr.sin6_addr, &cfg->peer_ip6,
			       sizeof(udp6_addr.sin6_addr));
			udp6_addr.sin6_port = cfg->peer_udp_port;
			err = kernel_connect(sock,
					     (struct sockaddr *)&udp6_addr,
					     sizeof(udp6_addr), 0);
		}
		if (err < 0)
			goto error;
	} else
#endif
	if (cfg->family == AF_INET) {
		struct sockaddr_in udp_addr;

		err = sock_create_kern(AF_INET, SOCK_DGRAM, 0, &sock);
		if (err < 0)
			goto error;

		sk_change_net(sock->sk, net);

		udp_addr.sin_family = AF_INET;
		udp_addr.sin_addr = cfg->local_ip;
		udp_addr.sin_port = cfg->local_udp_port;
		err = kernel_bind(sock, (struct sockaddr *)&udp_addr,
				  sizeof(udp_addr));
		if (err < 0)
			goto error;

		if (cfg->peer_udp_port) {
			udp_addr.sin_family = AF_INET;
			udp_addr.sin_addr = cfg->peer_ip;
			udp_addr.sin_port = cfg->peer_udp_port;
			err = kernel_connect(sock,
					     (struct sockaddr *)&udp_addr,
					     sizeof(udp_addr), 0);
			if (err < 0)
				goto error;
		}
	} else {
		return -EPFNOSUPPORT;
	}


	*sockp = sock;

	return 0;

error:
	if (sock) {
		kernel_sock_shutdown(sock, SHUT_RDWR);
		sk_release_kernel(sock->sk);
	}
	*sockp = NULL;
	return err;
}

void setup_udp_tunnel_sock(struct net *net, struct socket *sock,
			   struct udp_tunnel_sock_cfg *cfg)
{
	struct sock *sk = sock->sk;

	/* Disable multicast loopback */
	inet_sk(sk)->mc_loop = 0;

	rcu_assign_sk_user_data(sk, cfg->sk_user_data);

	udp_sk(sk)->encap_type = cfg->encap_type;
	udp_sk(sk)->encap_rcv = cfg->encap_rcv;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,9,0)
	udp_sk(sk)->encap_destroy = cfg->encap_destroy;
#endif

	udp_tunnel_encap_enable(sock);
}

void ovs_udp_gso(struct sk_buff *skb)
{
	int udp_offset = skb_transport_offset(skb);
	struct udphdr *uh;

	uh = udp_hdr(skb);
	uh->len = htons(skb->len - udp_offset);
}

void ovs_udp_csum_gso(struct sk_buff *skb)
{
	struct iphdr *iph = ip_hdr(skb);
	int udp_offset = skb_transport_offset(skb);

	ovs_udp_gso(skb);

	/* csum segment if tunnel sets skb with csum. The cleanest way
	 * to do this just to set it up from scratch. */
	skb->ip_summed = CHECKSUM_NONE;
	udp_set_csum(true, skb, iph->saddr, iph->daddr,
		     skb->len - udp_offset);
}

int udp_tunnel_xmit_skb(struct socket *sock, struct rtable *rt,
			struct sk_buff *skb, __be32 src, __be32 dst,
			__u8 tos, __u8 ttl, __be16 df, __be16 src_port,
			__be16 dst_port, bool xnet)
{
	struct udphdr *uh;

	__skb_push(skb, sizeof(*uh));
	skb_reset_transport_header(skb);
	uh = udp_hdr(skb);

	uh->dest = dst_port;
	uh->source = src_port;
	uh->len = htons(skb->len);

	udp_set_csum(true, skb, src, dst, skb->len);

	return iptunnel_xmit(sock->sk, rt, skb, src, dst, IPPROTO_UDP,
			     tos, ttl, df, xnet);
}

void udp_tunnel_sock_release(struct socket *sock)
{
	rcu_assign_sk_user_data(sock->sk, NULL);
	kernel_sock_shutdown(sock, SHUT_RDWR);
	sk_release_kernel(sock->sk);
}

#endif /* Linux version < 3.18 */