text: #ifndef __NET_DST_METADATA_H
  #define __NET_DST_METADATA_H 1
  
  #include <linux/skbuff.h>
  #include <net/ip_tunnels.h>
  #include <net/dst.h>
  
  enum metadata_type {
  	METADATA_IP_TUNNEL,
  	METADATA_HW_PORT_MUX,
  };
  
  struct hw_port_info {
  	struct net_device *lower_dev;
  	u32 port_id;
  };
  
  struct metadata_dst {
  	struct dst_entry		dst;
  	enum metadata_type		type;
  	union {
  		struct ip_tunnel_info	tun_info;
  		struct hw_port_info	port_info;
  	} u;
  };
  
  static inline struct metadata_dst *skb_metadata_dst(struct sk_buff *skb)
  {
  	struct metadata_dst *md_dst = (struct metadata_dst *) skb_dst(skb);
  
  	if (md_dst && md_dst->dst.flags & DST_METADATA)
  		return md_dst;
  
  	return NULL;
  }
  
  static inline struct ip_tunnel_info *skb_tunnel_info(struct sk_buff *skb)
  {
  	struct metadata_dst *md_dst = skb_metadata_dst(skb);
  	struct dst_entry *dst;
  
  	if (md_dst && md_dst->type == METADATA_IP_TUNNEL)
  		return &md_dst->u.tun_info;
  
  	dst = skb_dst(skb);
  	if (dst && dst->lwtstate)
  		return lwt_tun_info(dst->lwtstate);
  
  	return NULL;
  }
  
  static inline bool skb_valid_dst(const struct sk_buff *skb)
  {
  	struct dst_entry *dst = skb_dst(skb);
  
  	return dst && !(dst->flags & DST_METADATA);
  }
  
  static inline int skb_metadata_dst_cmp(const struct sk_buff *skb_a,
  				       const struct sk_buff *skb_b)
  {
  	const struct metadata_dst *a, *b;
  
  	if (!(skb_a->_skb_refdst | skb_b->_skb_refdst))
  		return 0;
  
  	a = (const struct metadata_dst *) skb_dst(skb_a);
  	b = (const struct metadata_dst *) skb_dst(skb_b);
  
  	if (!a != !b || a->type != b->type)
  		return 1;
  
  	switch (a->type) {
  	case METADATA_HW_PORT_MUX:
  		return memcmp(&a->u.port_info, &b->u.port_info,
  			      sizeof(a->u.port_info));
  	case METADATA_IP_TUNNEL:
  		return memcmp(&a->u.tun_info, &b->u.tun_info,
  			      sizeof(a->u.tun_info) +
  					 a->u.tun_info.options_len);
  	default:
  		return 1;
  	}
  }
  
  void metadata_dst_free(struct metadata_dst *);
  struct metadata_dst *metadata_dst_alloc(u8 optslen, enum metadata_type type,
  					gfp_t flags);
  struct metadata_dst __percpu *
  metadata_dst_alloc_percpu(u8 optslen, enum metadata_type type, gfp_t flags);
  
  static inline struct metadata_dst *tun_rx_dst(int md_size)
  {
  	struct metadata_dst *tun_dst;
  
  	tun_dst = metadata_dst_alloc(md_size, METADATA_IP_TUNNEL, GFP_ATOMIC);
  	if (!tun_dst)
  		return NULL;
  
  	tun_dst->u.tun_info.options_len = 0;
  	tun_dst->u.tun_info.mode = 0;
  	return tun_dst;
  }
  
  static inline struct metadata_dst *tun_dst_unclone(struct sk_buff *skb)
  {
  	struct metadata_dst *md_dst = skb_metadata_dst(skb);
  	int md_size;
  	struct metadata_dst *new_md;
  
  	if (!md_dst || md_dst->type != METADATA_IP_TUNNEL)
  		return ERR_PTR(-EINVAL);
  
  	md_size = md_dst->u.tun_info.options_len;
  	new_md = metadata_dst_alloc(md_size, METADATA_IP_TUNNEL, GFP_ATOMIC);
  	if (!new_md)
  		return ERR_PTR(-ENOMEM);
  
  	memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
  	       sizeof(struct ip_tunnel_info) + md_size);
  	skb_dst_drop(skb);
  	dst_hold(&new_md->dst);
  	skb_dst_set(skb, &new_md->dst);
  	return new_md;
  }
  
  static inline struct ip_tunnel_info *skb_tunnel_info_unclone(struct sk_buff *skb)
  {
  	struct metadata_dst *dst;
  
  	dst = tun_dst_unclone(skb);
  	if (IS_ERR(dst))
  		return NULL;
  
  	return &dst->u.tun_info;
  }
  
  static inline struct metadata_dst *__ip_tun_set_dst(__be32 saddr,
  						    __be32 daddr,
  						    __u8 tos, __u8 ttl,
  						    __be16 tp_dst,
  						    __be16 flags,
  						    __be64 tunnel_id,
  						    int md_size)
  {
  	struct metadata_dst *tun_dst;
  
  	tun_dst = tun_rx_dst(md_size);
  	if (!tun_dst)
  		return NULL;
  
  	ip_tunnel_key_init(&tun_dst->u.tun_info.key,
  			   saddr, daddr, tos, ttl,
  			   0, 0, tp_dst, tunnel_id, flags);
  	return tun_dst;
  }
  
  static inline struct metadata_dst *ip_tun_rx_dst(struct sk_buff *skb,
  						 __be16 flags,
  						 __be64 tunnel_id,
  						 int md_size)
  {
  	const struct iphdr *iph = ip_hdr(skb);
  
  	return __ip_tun_set_dst(iph->saddr, iph->daddr, iph->tos, iph->ttl,
  				0, flags, tunnel_id, md_size);
  }
  
  static inline struct metadata_dst *__ipv6_tun_set_dst(const struct in6_addr *saddr,
  						      const struct in6_addr *daddr,
  						      __u8 tos, __u8 ttl,
  						      __be16 tp_dst,
  						      __be32 label,
  						      __be16 flags,
  						      __be64 tunnel_id,
  						      int md_size)
  {
  	struct metadata_dst *tun_dst;
  	struct ip_tunnel_info *info;
  
  	tun_dst = tun_rx_dst(md_size);
  	if (!tun_dst)
  		return NULL;
  
  	info = &tun_dst->u.tun_info;
  	info->mode = IP_TUNNEL_INFO_IPV6;
  	info->key.tun_flags = flags;
  	info->key.tun_id = tunnel_id;
  	info->key.tp_src = 0;
  	info->key.tp_dst = tp_dst;
  
  	info->key.u.ipv6.src = *saddr;
  	info->key.u.ipv6.dst = *daddr;
  
  	info->key.tos = tos;
  	info->key.ttl = ttl;
  	info->key.label = label;
  
  	return tun_dst;
  }
  
  static inline struct metadata_dst *ipv6_tun_rx_dst(struct sk_buff *skb,
  						   __be16 flags,
  						   __be64 tunnel_id,
  						   int md_size)
  {
  	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
  
  	return __ipv6_tun_set_dst(&ip6h->saddr, &ip6h->daddr,
  				  ipv6_get_dsfield(ip6h), ip6h->hop_limit,
  				  0, ip6_flowlabel(ip6h), flags, tunnel_id,
  				  md_size);
  }
  #endif /* __NET_DST_METADATA_H */
  