text: #ifndef _IPV6_H
  #define _IPV6_H
  
  #include <linux/types.h>
  #include <linux/in6.h>
  #include <asm/byteorder.h>
  
  /* The latest drafts declared increase in minimal mtu up to 1280. */
  
  #define IPV6_MIN_MTU	1280
  
  /*
   *	Advanced API
   *	source interface/address selection, source routing, etc...
   *	*under construction*
   */
  
  
  struct in6_pktinfo {
  	struct in6_addr	ipi6_addr;
  	int		ipi6_ifindex;
  };
  
  struct ip6_mtuinfo {
  	struct sockaddr_in6	ip6m_addr;
  	__u32			ip6m_mtu;
  };
  
  struct in6_ifreq {
  	struct in6_addr	ifr6_addr;
  	__u32		ifr6_prefixlen;
  	int		ifr6_ifindex; 
  };
  
  #define IPV6_SRCRT_STRICT	0x01	/* Deprecated; will be removed */
  #define IPV6_SRCRT_TYPE_0	0	/* Deprecated; will be removed */
  #define IPV6_SRCRT_TYPE_2	2	/* IPv6 type 2 Routing Header	*/
  
  /*
   *	routing header
   */
  struct ipv6_rt_hdr {
  	__u8		nexthdr;
  	__u8		hdrlen;
  	__u8		type;
  	__u8		segments_left;
  
  	/*
  	 *	type specific data
  	 *	variable length field
  	 */
  };
  
  
  struct ipv6_opt_hdr {
  	__u8 		nexthdr;
  	__u8 		hdrlen;
  	/* 
  	 * TLV encoded option data follows.
  	 */
  } __attribute__((packed));	/* required for some archs */
  
  #define ipv6_destopt_hdr ipv6_opt_hdr
  #define ipv6_hopopt_hdr  ipv6_opt_hdr
  
  #ifdef __KERNEL__
  #define ipv6_optlen(p)  (((p)->hdrlen+1) << 3)
  #endif
  
  /*
   *	routing header type 0 (used in cmsghdr struct)
   */
  
  struct rt0_hdr {
  	struct ipv6_rt_hdr	rt_hdr;
  	__u32			reserved;
  	struct in6_addr		addr[0];
  
  #define rt0_type		rt_hdr.type
  };
  
  /*
   *	routing header type 2
   */
  
  struct rt2_hdr {
  	struct ipv6_rt_hdr	rt_hdr;
  	__u32			reserved;
  	struct in6_addr		addr;
  
  #define rt2_type		rt_hdr.type
  };
  
  /*
   *	home address option in destination options header
   */
  
  struct ipv6_destopt_hao {
  	__u8			type;
  	__u8			length;
  	struct in6_addr		addr;
  } __attribute__((packed));
  
  /*
   *	IPv6 fixed header
   *
   *	BEWARE, it is incorrect. The first 4 bits of flow_lbl
   *	are glued to priority now, forming "class".
   */
  
  struct ipv6hdr {
  #if defined(__LITTLE_ENDIAN_BITFIELD)
  	__u8			priority:4,
  				version:4;
  #elif defined(__BIG_ENDIAN_BITFIELD)
  	__u8			version:4,
  				priority:4;
  #else
  #error	"Please fix <asm/byteorder.h>"
  #endif
  	__u8			flow_lbl[3];
  
  	__be16			payload_len;
  	__u8			nexthdr;
  	__u8			hop_limit;
  
  	struct	in6_addr	saddr;
  	struct	in6_addr	daddr;
  };
  
  #ifdef __KERNEL__
  /*
   * This structure contains configuration options per IPv6 link.
   */
  struct ipv6_devconf {
  	__s32		forwarding;
  	__s32		hop_limit;
  	__s32		mtu6;
  	__s32		accept_ra;
  	__s32		accept_redirects;
  	__s32		autoconf;
  	__s32		dad_transmits;
  	__s32		rtr_solicits;
  	__s32		rtr_solicit_interval;
  	__s32		rtr_solicit_delay;
  	__s32		force_mld_version;
  #ifdef CONFIG_IPV6_PRIVACY
  	__s32		use_tempaddr;
  	__s32		temp_valid_lft;
  	__s32		temp_prefered_lft;
  	__s32		regen_max_retry;
  	__s32		max_desync_factor;
  #endif
  	__s32		max_addresses;
  	__s32		accept_ra_defrtr;
  	__s32		accept_ra_pinfo;
  #ifdef CONFIG_IPV6_ROUTER_PREF
  	__s32		accept_ra_rtr_pref;
  	__s32		rtr_probe_interval;
  #ifdef CONFIG_IPV6_ROUTE_INFO
  	__s32		accept_ra_rt_info_max_plen;
  #endif
  #endif
  	__s32		accept_ra_rt_table;
  	__s32		proxy_ndp;
  	__s32		accept_source_route;
  #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
  	__s32		optimistic_dad;
  	__s32		use_optimistic;
  #endif
  #ifdef CONFIG_IPV6_MROUTE
  	__s32		mc_forwarding;
  #endif
  	__s32		disable_ipv6;
  	__s32		accept_dad;
  	__s32		force_tllao;
  	void		*sysctl;
  };
  
  struct ipv6_params {
  	__s32 disable_ipv6;
  	__s32 autoconf;
  };
  extern struct ipv6_params ipv6_defaults;
  #endif
  
  /* index values for the variables in ipv6_devconf */
  enum {
  	DEVCONF_FORWARDING = 0,
  	DEVCONF_HOPLIMIT,
  	DEVCONF_MTU6,
  	DEVCONF_ACCEPT_RA,
  	DEVCONF_ACCEPT_REDIRECTS,
  	DEVCONF_AUTOCONF,
  	DEVCONF_DAD_TRANSMITS,
  	DEVCONF_RTR_SOLICITS,
  	DEVCONF_RTR_SOLICIT_INTERVAL,
  	DEVCONF_RTR_SOLICIT_DELAY,
  	DEVCONF_USE_TEMPADDR,
  	DEVCONF_TEMP_VALID_LFT,
  	DEVCONF_TEMP_PREFERED_LFT,
  	DEVCONF_REGEN_MAX_RETRY,
  	DEVCONF_MAX_DESYNC_FACTOR,
  	DEVCONF_MAX_ADDRESSES,
  	DEVCONF_FORCE_MLD_VERSION,
  	DEVCONF_ACCEPT_RA_DEFRTR,
  	DEVCONF_ACCEPT_RA_PINFO,
  	DEVCONF_ACCEPT_RA_RTR_PREF,
  	DEVCONF_RTR_PROBE_INTERVAL,
  	DEVCONF_ACCEPT_RA_RT_INFO_MAX_PLEN,
  	DEVCONF_PROXY_NDP,
  	DEVCONF_OPTIMISTIC_DAD,
  	DEVCONF_ACCEPT_SOURCE_ROUTE,
  	DEVCONF_MC_FORWARDING,
  	DEVCONF_DISABLE_IPV6,
  	DEVCONF_ACCEPT_DAD,
  	DEVCONF_FORCE_TLLAO,
  	DEVCONF_ACCEPT_RA_RT_TABLE,	
  	DEVCONF_USE_OPTIMISTIC,	
  	DEVCONF_MAX
  };
  
  #ifdef __KERNEL__
  #include <linux/icmpv6.h>
  #include <linux/tcp.h>
  #include <linux/udp.h>
  
  #include <net/inet_sock.h>
  
  static inline struct ipv6hdr *ipv6_hdr(const struct sk_buff *skb)
  {
  	return (struct ipv6hdr *)skb_network_header(skb);
  }
  
  static inline struct ipv6hdr *ipipv6_hdr(const struct sk_buff *skb)
  {
  	return (struct ipv6hdr *)skb_transport_header(skb);
  }
  
  static inline __u8 ipv6_tclass(const struct ipv6hdr *iph)
  {
  	return (ntohl(*(__be32 *)iph) >> 20) & 0xff;
  }
  
  /* 
     This structure contains results of exthdrs parsing
     as offsets from skb->nh.
   */
  
  struct inet6_skb_parm {
  	int			iif;
  	__u16			ra;
  	__u16			hop;
  	__u16			dst0;
  	__u16			srcrt;
  	__u16			dst1;
  	__u16			lastopt;
  	__u16			nhoff;
  	__u16			flags;
  #if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)
  	__u16			dsthao;
  #endif
  
  #define IP6SKB_XFRM_TRANSFORMED	1
  #define IP6SKB_FORWARDED	2
  #define IP6SKB_REROUTED		4
  #define IP6SKB_FRAGMENTED      16
  };
  
  #define IP6CB(skb)	((struct inet6_skb_parm*)((skb)->cb))
  #define IP6CBMTU(skb)	((struct ip6_mtuinfo *)((skb)->cb))
  
  static inline int inet6_iif(const struct sk_buff *skb)
  {
  	return IP6CB(skb)->iif;
  }
  
  struct inet6_request_sock {
  	struct in6_addr		loc_addr;
  	struct in6_addr		rmt_addr;
  	struct sk_buff		*pktopts;
  	int			iif;
  };
  
  struct tcp6_request_sock {
  	struct tcp_request_sock	  tcp6rsk_tcp;
  	struct inet6_request_sock tcp6rsk_inet6;
  };
  
  struct ipv6_mc_socklist;
  struct ipv6_ac_socklist;
  struct ipv6_fl_socklist;
  
  /**
   * struct ipv6_pinfo - ipv6 private area
   *
   * In the struct sock hierarchy (tcp6_sock, upd6_sock, etc)
   * this _must_ be the last member, so that inet6_sk_generic
   * is able to calculate its offset from the base struct sock
   * by using the struct proto->slab_obj_size member. -acme
   */
  struct ipv6_pinfo {
  	struct in6_addr 	saddr;
  	struct in6_addr 	rcv_saddr;
  	struct in6_addr		daddr;
  	struct in6_pktinfo	sticky_pktinfo;
  	struct in6_addr		*daddr_cache;
  #ifdef CONFIG_IPV6_SUBTREES
  	struct in6_addr		*saddr_cache;
  #endif
  
  	__be32			flow_label;
  	__u32			frag_size;
  
  	/*
  	 * Packed in 16bits.
  	 * Omit one shift by by putting the signed field at MSB.
  	 */
  #if defined(__BIG_ENDIAN_BITFIELD)
  	__s16			hop_limit:9;
  	__u16			__unused_1:7;
  #else
  	__u16			__unused_1:7;
  	__s16			hop_limit:9;
  #endif
  
  #if defined(__BIG_ENDIAN_BITFIELD)
  	/* Packed in 16bits. */
  	__s16			mcast_hops:9;
  	__u16			__unused_2:6,
  				mc_loop:1;
  #else
  	__u16			mc_loop:1,
  				__unused_2:6;
  	__s16			mcast_hops:9;
  #endif
  	int			ucast_oif;
  	int			mcast_oif;
  
  	/* pktoption flags */
  	union {
  		struct {
  			__u16	srcrt:1,
  				osrcrt:1,
  			        rxinfo:1,
  			        rxoinfo:1,
  				rxhlim:1,
  				rxohlim:1,
  				hopopts:1,
  				ohopopts:1,
  				dstopts:1,
  				odstopts:1,
                                  rxflow:1,
  				rxtclass:1,
  				rxpmtu:1,
  				rxorigdstaddr:1;
  				/* 2 bits hole */
  		} bits;
  		__u16		all;
  	} rxopt;
  
  	/* sockopt flags */
  	__u16			recverr:1,
  	                        sndflow:1,
  				pmtudisc:2,
  				ipv6only:1,
  				srcprefs:3,	/* 001: prefer temporary address
  						 * 010: prefer public address
  						 * 100: prefer care-of address
  						 */
  				dontfrag:1;
  	__u8			min_hopcount;
  	__u8			tclass;
  	__u8			rcv_tclass;
  
  	__u32			dst_cookie;
  
  	struct ipv6_mc_socklist	__rcu *ipv6_mc_list;
  	struct ipv6_ac_socklist	*ipv6_ac_list;
  	struct ipv6_fl_socklist *ipv6_fl_list;
  
  	struct ipv6_txoptions	*opt;
  	struct sk_buff		*pktoptions;
  	struct sk_buff		*rxpmtu;
  	struct {
  		struct ipv6_txoptions *opt;
  		u8 hop_limit;
  		u8 tclass;
  	} cork;
  };
  
  /* WARNING: don't change the layout of the members in {raw,udp,tcp}6_sock! */
  struct raw6_sock {
  	/* inet_sock has to be the first member of raw6_sock */
  	struct inet_sock	inet;
  	__u32			checksum;	/* perform checksum */
  	__u32			offset;		/* checksum offset  */
  	struct icmp6_filter	filter;
  	__u32			ip6mr_table;
  	/* ipv6_pinfo has to be the last member of raw6_sock, see inet6_sk_generic */
  	struct ipv6_pinfo	inet6;
  };
  
  struct udp6_sock {
  	struct udp_sock	  udp;
  	/* ipv6_pinfo has to be the last member of udp6_sock, see inet6_sk_generic */
  	struct ipv6_pinfo inet6;
  };
  
  struct tcp6_sock {
  	struct tcp_sock	  tcp;
  	/* ipv6_pinfo has to be the last member of tcp6_sock, see inet6_sk_generic */
  	struct ipv6_pinfo inet6;
  };
  
  extern int inet6_sk_rebuild_header(struct sock *sk);
  
  #if IS_ENABLED(CONFIG_IPV6)
  static inline struct ipv6_pinfo * inet6_sk(const struct sock *__sk)
  {
  	return inet_sk(__sk)->pinet6;
  }
  
  static inline struct inet6_request_sock *
  			inet6_rsk(const struct request_sock *rsk)
  {
  	return (struct inet6_request_sock *)(((u8 *)rsk) +
  					     inet_rsk(rsk)->inet6_rsk_offset);
  }
  
  static inline u32 inet6_rsk_offset(struct request_sock *rsk)
  {
  	return rsk->rsk_ops->obj_size - sizeof(struct inet6_request_sock);
  }
  
  static inline struct request_sock *inet6_reqsk_alloc(struct request_sock_ops *ops)
  {
  	struct request_sock *req = reqsk_alloc(ops);
  
  	if (req != NULL) {
  		inet_rsk(req)->inet6_rsk_offset = inet6_rsk_offset(req);
  		inet6_rsk(req)->pktopts = NULL;
  	}
  
  	return req;
  }
  
  static inline struct raw6_sock *raw6_sk(const struct sock *sk)
  {
  	return (struct raw6_sock *)sk;
  }
  
  static inline void inet_sk_copy_descendant(struct sock *sk_to,
  					   const struct sock *sk_from)
  {
  	int ancestor_size = sizeof(struct inet_sock);
  
  	if (sk_from->sk_family == PF_INET6)
  		ancestor_size += sizeof(struct ipv6_pinfo);
  
  	__inet_sk_copy_descendant(sk_to, sk_from, ancestor_size);
  }
  
  #define __ipv6_only_sock(sk)	(inet6_sk(sk)->ipv6only)
  #define ipv6_only_sock(sk)	((sk)->sk_family == PF_INET6 && __ipv6_only_sock(sk))
  
  struct inet6_timewait_sock {
  	struct in6_addr tw_v6_daddr;
  	struct in6_addr	tw_v6_rcv_saddr;
  };
  
  struct tcp6_timewait_sock {
  	struct tcp_timewait_sock   tcp6tw_tcp;
  	struct inet6_timewait_sock tcp6tw_inet6;
  };
  
  static inline u16 inet6_tw_offset(const struct proto *prot)
  {
  	return prot->twsk_prot->twsk_obj_size -
  			sizeof(struct inet6_timewait_sock);
  }
  
  static inline struct inet6_timewait_sock *inet6_twsk(const struct sock *sk)
  {
  	return (struct inet6_timewait_sock *)(((u8 *)sk) +
  					      inet_twsk(sk)->tw_ipv6_offset);
  }
  
  static inline struct in6_addr *__inet6_rcv_saddr(const struct sock *sk)
  {
  	return likely(sk->sk_state != TCP_TIME_WAIT) ?
  		&inet6_sk(sk)->rcv_saddr : &inet6_twsk(sk)->tw_v6_rcv_saddr;
  }
  
  static inline struct in6_addr *inet6_rcv_saddr(const struct sock *sk)
  {
  	return sk->sk_family == AF_INET6 ? __inet6_rcv_saddr(sk) : NULL;
  }
  
  static inline int inet_v6_ipv6only(const struct sock *sk)
  {
  	return likely(sk->sk_state != TCP_TIME_WAIT) ?
  		ipv6_only_sock(sk) : inet_twsk(sk)->tw_ipv6only;
  }
  #else
  #define __ipv6_only_sock(sk)	0
  #define ipv6_only_sock(sk)	0
  
  static inline struct ipv6_pinfo * inet6_sk(const struct sock *__sk)
  {
  	return NULL;
  }
  
  static inline struct inet6_request_sock *
  			inet6_rsk(const struct request_sock *rsk)
  {
  	return NULL;
  }
  
  static inline struct raw6_sock *raw6_sk(const struct sock *sk)
  {
  	return NULL;
  }
  
  #define __inet6_rcv_saddr(__sk)	NULL
  #define inet6_rcv_saddr(__sk)	NULL
  #define tcp_twsk_ipv6only(__sk)		0
  #define inet_v6_ipv6only(__sk)		0
  #endif /* IS_ENABLED(CONFIG_IPV6) */
  
  #define INET6_MATCH(__sk, __net, __hash, __saddr, __daddr, __ports, __dif)\
  	(((__sk)->sk_hash == (__hash)) && sock_net((__sk)) == (__net)	&& \
  	 ((*((__portpair *)&(inet_sk(__sk)->inet_dport))) == (__ports)) && \
  	 ((__sk)->sk_family		== AF_INET6)		&& \
  	 ipv6_addr_equal(&inet6_sk(__sk)->daddr, (__saddr))	&& \
  	 ipv6_addr_equal(&inet6_sk(__sk)->rcv_saddr, (__daddr))	&& \
  	 (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))
  
  #define INET6_TW_MATCH(__sk, __net, __hash, __saddr, __daddr, __ports, __dif) \
  	(((__sk)->sk_hash == (__hash)) && sock_net((__sk)) == (__net)	&& \
  	 (*((__portpair *)&(inet_twsk(__sk)->tw_dport)) == (__ports))	&& \
  	 ((__sk)->sk_family	       == PF_INET6)			&& \
  	 (ipv6_addr_equal(&inet6_twsk(__sk)->tw_v6_daddr, (__saddr)))	&& \
  	 (ipv6_addr_equal(&inet6_twsk(__sk)->tw_v6_rcv_saddr, (__daddr))) && \
  	 (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))
  
  #endif /* __KERNEL__ */
  
  #endif /* _IPV6_H */
  