text: #include <uapi/linux/bpf.h>
  #include "bpf_helpers.h"
  #include <uapi/linux/in.h>
  #include <uapi/linux/if.h>
  #include <uapi/linux/if_ether.h>
  #include <uapi/linux/ip.h>
  #include <uapi/linux/ipv6.h>
  #include <uapi/linux/if_tunnel.h>
  #define IP_MF		0x2000
  #define IP_OFFSET	0x1FFF
  
  struct vlan_hdr {
  	__be16 h_vlan_TCI;
  	__be16 h_vlan_encapsulated_proto;
  };
  
  struct bpf_flow_keys {
  	__be32 src;
  	__be32 dst;
  	union {
  		__be32 ports;
  		__be16 port16[2];
  	};
  	__u16 thoff;
  	__u8 ip_proto;
  };
  
  static inline int proto_ports_offset(__u64 proto)
  {
  	switch (proto) {
  	case IPPROTO_TCP:
  	case IPPROTO_UDP:
  	case IPPROTO_DCCP:
  	case IPPROTO_ESP:
  	case IPPROTO_SCTP:
  	case IPPROTO_UDPLITE:
  		return 0;
  	case IPPROTO_AH:
  		return 4;
  	default:
  		return 0;
  	}
  }
  
  static inline int ip_is_fragment(struct __sk_buff *ctx, __u64 nhoff)
  {
  	return load_half(ctx, nhoff + offsetof(struct iphdr, frag_off))
  		& (IP_MF | IP_OFFSET);
  }
  
  static inline __u32 ipv6_addr_hash(struct __sk_buff *ctx, __u64 off)
  {
  	__u64 w0 = load_word(ctx, off);
  	__u64 w1 = load_word(ctx, off + 4);
  	__u64 w2 = load_word(ctx, off + 8);
  	__u64 w3 = load_word(ctx, off + 12);
  
  	return (__u32)(w0 ^ w1 ^ w2 ^ w3);
  }
  
  static inline __u64 parse_ip(struct __sk_buff *skb, __u64 nhoff, __u64 *ip_proto,
  			     struct bpf_flow_keys *flow)
  {
  	__u64 verlen;
  
  	if (unlikely(ip_is_fragment(skb, nhoff)))
  		*ip_proto = 0;
  	else
  		*ip_proto = load_byte(skb, nhoff + offsetof(struct iphdr, protocol));
  
  	if (*ip_proto != IPPROTO_GRE) {
  		flow->src = load_word(skb, nhoff + offsetof(struct iphdr, saddr));
  		flow->dst = load_word(skb, nhoff + offsetof(struct iphdr, daddr));
  	}
  
  	verlen = load_byte(skb, nhoff + 0/*offsetof(struct iphdr, ihl)*/);
  	if (likely(verlen == 0x45))
  		nhoff += 20;
  	else
  		nhoff += (verlen & 0xF) << 2;
  
  	return nhoff;
  }
  
  static inline __u64 parse_ipv6(struct __sk_buff *skb, __u64 nhoff, __u64 *ip_proto,
  			       struct bpf_flow_keys *flow)
  {
  	*ip_proto = load_byte(skb,
  			      nhoff + offsetof(struct ipv6hdr, nexthdr));
  	flow->src = ipv6_addr_hash(skb,
  				   nhoff + offsetof(struct ipv6hdr, saddr));
  	flow->dst = ipv6_addr_hash(skb,
  				   nhoff + offsetof(struct ipv6hdr, daddr));
  	nhoff += sizeof(struct ipv6hdr);
  
  	return nhoff;
  }
  
  static inline bool flow_dissector(struct __sk_buff *skb, struct bpf_flow_keys *flow)
  {
  	__u64 nhoff = ETH_HLEN;
  	__u64 ip_proto;
  	__u64 proto = load_half(skb, 12);
  	int poff;
  
  	if (proto == ETH_P_8021AD) {
  		proto = load_half(skb, nhoff + offsetof(struct vlan_hdr,
  							h_vlan_encapsulated_proto));
  		nhoff += sizeof(struct vlan_hdr);
  	}
  
  	if (proto == ETH_P_8021Q) {
  		proto = load_half(skb, nhoff + offsetof(struct vlan_hdr,
  							h_vlan_encapsulated_proto));
  		nhoff += sizeof(struct vlan_hdr);
  	}
  
  	if (likely(proto == ETH_P_IP))
  		nhoff = parse_ip(skb, nhoff, &ip_proto, flow);
  	else if (proto == ETH_P_IPV6)
  		nhoff = parse_ipv6(skb, nhoff, &ip_proto, flow);
  	else
  		return false;
  
  	switch (ip_proto) {
  	case IPPROTO_GRE: {
  		struct gre_hdr {
  			__be16 flags;
  			__be16 proto;
  		};
  
  		__u64 gre_flags = load_half(skb,
  					    nhoff + offsetof(struct gre_hdr, flags));
  		__u64 gre_proto = load_half(skb,
  					    nhoff + offsetof(struct gre_hdr, proto));
  
  		if (gre_flags & (GRE_VERSION|GRE_ROUTING))
  			break;
  
  		proto = gre_proto;
  		nhoff += 4;
  		if (gre_flags & GRE_CSUM)
  			nhoff += 4;
  		if (gre_flags & GRE_KEY)
  			nhoff += 4;
  		if (gre_flags & GRE_SEQ)
  			nhoff += 4;
  
  		if (proto == ETH_P_8021Q) {
  			proto = load_half(skb,
  					  nhoff + offsetof(struct vlan_hdr,
  							   h_vlan_encapsulated_proto));
  			nhoff += sizeof(struct vlan_hdr);
  		}
  
  		if (proto == ETH_P_IP)
  			nhoff = parse_ip(skb, nhoff, &ip_proto, flow);
  		else if (proto == ETH_P_IPV6)
  			nhoff = parse_ipv6(skb, nhoff, &ip_proto, flow);
  		else
  			return false;
  		break;
  	}
  	case IPPROTO_IPIP:
  		nhoff = parse_ip(skb, nhoff, &ip_proto, flow);
  		break;
  	case IPPROTO_IPV6:
  		nhoff = parse_ipv6(skb, nhoff, &ip_proto, flow);
  		break;
  	default:
  		break;
  	}
  
  	flow->ip_proto = ip_proto;
  	poff = proto_ports_offset(ip_proto);
  	if (poff >= 0) {
  		nhoff += poff;
  		flow->ports = load_word(skb, nhoff);
  	}
  
  	flow->thoff = (__u16) nhoff;
  
  	return true;
  }
  
  struct pair {
  	long packets;
  	long bytes;
  };
  
  struct bpf_map_def SEC("maps") hash_map = {
  	.type = BPF_MAP_TYPE_HASH,
  	.key_size = sizeof(__be32),
  	.value_size = sizeof(struct pair),
  	.max_entries = 1024,
  };
  
  SEC("socket2")
  int bpf_prog2(struct __sk_buff *skb)
  {
  	struct bpf_flow_keys flow;
  	struct pair *value;
  	u32 key;
  
  	if (!flow_dissector(skb, &flow))
  		return 0;
  
  	key = flow.dst;
  	value = bpf_map_lookup_elem(&hash_map, &key);
  	if (value) {
  		__sync_fetch_and_add(&value->packets, 1);
  		__sync_fetch_and_add(&value->bytes, skb->len);
  	} else {
  		struct pair val = {1, skb->len};
  
  		bpf_map_update_elem(&hash_map, &key, &val, BPF_ANY);
  	}
  	return 0;
  }
  
  char _license[] SEC("license") = "GPL";
  