include/linux/netfilter_bridge/ebt_among.h

   1 #ifndef __LINUX_BRIDGE_EBT_AMONG_H
   2 #define __LINUX_BRIDGE_EBT_AMONG_H
   3
   4 #include <linux/types.h>
   5
   6 #define EBT_AMONG_DST 0x01
   7 #define EBT_AMONG_SRC 0x02
   8
   9 /* Grzegorz Borowiak <grzes@gnu.univ.gda.pl> 2003
  10  *
  11  * Write-once-read-many hash table, used for checking if a given
  12  * MAC address belongs to a set or not and possibly for checking
  13  * if it is related with a given IPv4 address.
  14  *
  15  * The hash value of an address is its last byte.
  16  *
  17  * In real-world ethernet addresses, values of the last byte are
  18  * evenly distributed and there is no need to consider other bytes.
  19  * It would only slow the routines down.
  20  *
  21  * For MAC address comparison speedup reasons, we introduce a trick.
  22  * MAC address is mapped onto an array of two 32-bit integers.
  23  * This pair of integers is compared with MAC addresses in the
  24  * hash table, which are stored also in form of pairs of integers
  25  * (in `cmp' array). This is quick as it requires only two elementary
  26  * number comparisons in worst case. Further, we take advantage of
  27  * fact that entropy of 3 last bytes of address is larger than entropy
  28  * of 3 first bytes. So first we compare 4 last bytes of addresses and
  29  * if they are the same we compare 2 first.
  30  *
  31  * Yes, it is a memory overhead, but in 2003 AD, who cares?
  32  */
  33
  34 struct ebt_mac_wormhash_tuple {
  35         __u32 cmp[2];
  36         __be32 ip;
  37 };
  38
  39 struct ebt_mac_wormhash {
  40         int table[257];
  41         int poolsize;
  42         struct ebt_mac_wormhash_tuple pool[0];
  43 };
  44
  45 #define ebt_mac_wormhash_size(x) ((x) ? sizeof(struct ebt_mac_wormhash) \
  46                 + (x)->poolsize * sizeof(struct ebt_mac_wormhash_tuple) : 0)
  47
  48 struct ebt_among_info {
  49         int wh_dst_ofs;
  50         int wh_src_ofs;
  51         int bitmask;
  52 };
  53
  54 #define EBT_AMONG_DST_NEG 0x1
  55 #define EBT_AMONG_SRC_NEG 0x2
  56
  57 #define ebt_among_wh_dst(x) ((x)->wh_dst_ofs ? \
  58         (struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_dst_ofs) : NULL)
  59 #define ebt_among_wh_src(x) ((x)->wh_src_ofs ? \
  60         (struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_src_ofs) : NULL)
  61
  62 #define EBT_AMONG_MATCH "among"
  63
  64 #endif