int healthchecker()

in katran/lib/bpf/healthchecking_ipip.c [89:157]
52 lines of code
8 McCabe index (conditional complexity)

int healthchecker(struct __sk_buff* skb) {
  int ret = 0;
  int tun_flag = 0;
  __u32 ifindex;
  __u32 somark = skb->mark;
  __u32 v4_intf_pos = 1;
  __u32 v6_intf_pos = 2;
  struct bpf_tunnel_key tkey = {};

  __u32 stats_key = GENERIC_STATS_INDEX;
  struct hc_stats* prog_stats;

  prog_stats = bpf_map_lookup_elem(&hc_stats_map, &stats_key);
  if (!prog_stats) {
    return TC_ACT_UNSPEC;
  }

  if (skb->mark == 0) {
    prog_stats->pckts_skipped += 1;
    return TC_ACT_UNSPEC;
  }

  struct hc_real_definition* real = bpf_map_lookup_elem(&hc_reals_map, &somark);
  if (!real) {
    // some strange (w/ fwmark; but not a healthcheck) local packet
    prog_stats->pckts_skipped += 1;
    return TC_ACT_UNSPEC;
  }

  if (skb->len > MAX_PACKET_SIZE) {
    // do not allow packets bigger than the specified size
    prog_stats->pckts_dropped += 1;
    prog_stats->pckts_too_big += 1;
    return TC_ACT_SHOT;
  }

  __u32* v4_intf_ifindex = bpf_map_lookup_elem(&hc_ctrl_map, &v4_intf_pos);
  if (!v4_intf_ifindex) {
    // we dont have ifindex for ipip v4 interface
    // not much we can do without it. Drop packet so that hc will fail
    prog_stats->pckts_dropped += 1;
    return TC_ACT_SHOT;
  }

  __u32* v6_intf_ifindex = bpf_map_lookup_elem(&hc_ctrl_map, &v6_intf_pos);
  if (!v6_intf_ifindex) {
    prog_stats->pckts_dropped += 1;
    return TC_ACT_SHOT;
  }

  tkey.tunnel_ttl = DEFAULT_TTL;

  // to prevent recursion, when encaped packet would run through this filter
  skb->mark = 0;

  if (real->flags == V6DADDR) {
    // the dst is v6.
    tun_flag = BPF_F_TUNINFO_IPV6;
    memcpy(tkey.remote_ipv6, real->v6daddr, 16);
    ifindex = *v6_intf_ifindex;
  } else {
    // the dst is v4
    tkey.remote_ipv4 = real->daddr;
    ifindex = *v4_intf_ifindex;
  }
  prog_stats->pckts_processed += 1;
  bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), tun_flag);
  return bpf_redirect(ifindex, REDIRECT_EGRESS);
}