#ifndef __LINUX_GRE_H#define __LINUX_GRE_H #include <linux/skbuff.h> #define GREPROTO_CISCO		0#define GREPROTO_PPTP		1#define GREPROTO_MAX		2 struct gre_protocol {	int  (*handler)(struct sk_buff *skb);	void (*err_handler)(struct sk_buff *skb, u32 info);}; int gre_add_protocol(const struct gre_protocol *proto, u8 version);int gre_del_protocol(const struct gre_protocol *proto, u8 version); #endif