LXR linux/include/uapi/linux/netfilter_bridge/ebt

   1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
   2#ifndef __LINUX_BRIDGE_EBT_AMONG_H
   3#define __LINUX_BRIDGE_EBT_AMONG_H
   4
   5#include <linux/types.h>
   6
   7#define EBT_AMONG_DST 0x01
   8#define EBT_AMONG_SRC 0x02
   9
  10/* Grzegorz Borowiak <grzes@gnu.univ.gda.pl> 2003
  11 * 
  12 * Write-once-read-many hash table, used for checking if a given
  13 * MAC address belongs to a set or not and possibly for checking
  14 * if it is related with a given IPv4 address.
  15 *
  16 * The hash value of an address is its last byte.
  17 * 
  18 * In real-world ethernet addresses, values of the last byte are
  19 * evenly distributed and there is no need to consider other bytes.
  20 * It would only slow the routines down.
  21 *
  22 * For MAC address comparison speedup reasons, we introduce a trick.
  23 * MAC address is mapped onto an array of two 32-bit integers.
  24 * This pair of integers is compared with MAC addresses in the
  25 * hash table, which are stored also in form of pairs of integers
  26 * (in `cmp' array). This is quick as it requires only two elementary
  27 * number comparisons in worst case. Further, we take advantage of
  28 * fact that entropy of 3 last bytes of address is larger than entropy
  29 * of 3 first bytes. So first we compare 4 last bytes of addresses and
  30 * if they are the same we compare 2 first.
  31 *
  32 * Yes, it is a memory overhead, but in 2003 AD, who cares?
  33 */
  34
  35struct ebt_mac_wormhash_tuple {
  36        __u32 cmp[2];
  37        __be32 ip;
  38};
  39
  40struct ebt_mac_wormhash {
  41        int table[257];
  42        int poolsize;
  43        struct ebt_mac_wormhash_tuple pool[0];
  44};
  45
  46#define ebt_mac_wormhash_size(x) ((x) ? sizeof(struct ebt_mac_wormhash) \
  47                + (x)->poolsize * sizeof(struct ebt_mac_wormhash_tuple) : 0)
  48
  49struct ebt_among_info {
  50        int wh_dst_ofs;
  51        int wh_src_ofs;
  52        int bitmask;
  53};
  54
  55#define EBT_AMONG_DST_NEG 0x1
  56#define EBT_AMONG_SRC_NEG 0x2
  57
  58#define ebt_among_wh_dst(x) ((x)->wh_dst_ofs ? \
  59        (struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_dst_ofs) : NULL)
  60#define ebt_among_wh_src(x) ((x)->wh_src_ofs ? \
  61        (struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_src_ofs) : NULL)
  62
  63#define EBT_AMONG_MATCH "among"
  64
  65#endif
  66