1. 根目录:
2. include
3. net
4. esp.h

#ifndef _NET_ESP_H
#define _NET_ESP_H

#include <linux/skbuff.h>

struct ip_esp_hdr;

static inline struct ip_esp_hdr *ip_esp_hdr(const struct sk_buff *skb)
{
	return (struct ip_esp_hdr *)skb_transport_header(skb);
}

#endif