/*
   * Copyright (c) 2006 Patrick McHardy <kaber@trash.net>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * Based on ipt_random and ipt_nth by Fabrice MARIE <fabrice@netfilter.org>.
   */
  
  #include <linux/init.h>
  #include <linux/spinlock.h>
  #include <linux/skbuff.h>
  #include <linux/net.h>

  #include <linux/slab.h>

  
  #include <linux/netfilter/xt_statistic.h>
  #include <linux/netfilter/x_tables.h>

  #include <linux/module.h>

  struct xt_statistic_priv {

  	atomic_t count;
  } ____cacheline_aligned_in_smp;

  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");

  MODULE_DESCRIPTION("Xtables: statistics-based matching (\"Nth\", random)");

  MODULE_ALIAS("ipt_statistic");
  MODULE_ALIAS("ip6t_statistic");

  static bool

  statistic_mt(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_statistic_info *info = par->matchinfo;

  	bool ret = info->flags & XT_STATISTIC_INVERT;

  	int nval, oval;

  
  	switch (info->mode) {
  	case XT_STATISTIC_MODE_RANDOM:
  		if ((net_random() & 0x7FFFFFFF) < info->u.random.probability)

  			ret = !ret;

  		break;
  	case XT_STATISTIC_MODE_NTH:

  		do {
  			oval = atomic_read(&info->master->count);
  			nval = (oval == info->u.nth.every) ? 0 : oval + 1;
  		} while (atomic_cmpxchg(&info->master->count, oval, nval) != oval);
  		if (nval == 0)

  			ret = !ret;

  		break;
  	}
  
  	return ret;
  }

  static int statistic_mt_check(const struct xt_mtchk_param *par)

  {

  	struct xt_statistic_info *info = par->matchinfo;

  
  	if (info->mode > XT_STATISTIC_MODE_MAX ||
  	    info->flags & ~XT_STATISTIC_MASK)

  		return -EINVAL;

  
  	info->master = kzalloc(sizeof(*info->master), GFP_KERNEL);

  	if (info->master == NULL)

  		return -ENOMEM;

  	atomic_set(&info->master->count, info->u.nth.count);

  	return 0;

  }

  static void statistic_mt_destroy(const struct xt_mtdtor_param *par)
  {
  	const struct xt_statistic_info *info = par->matchinfo;
  
  	kfree(info->master);
  }

  static struct xt_match xt_statistic_mt_reg __read_mostly = {
  	.name       = "statistic",
  	.revision   = 0,
  	.family     = NFPROTO_UNSPEC,
  	.match      = statistic_mt,
  	.checkentry = statistic_mt_check,

  	.destroy    = statistic_mt_destroy,

  	.matchsize  = sizeof(struct xt_statistic_info),
  	.me         = THIS_MODULE,

  };

  static int __init statistic_mt_init(void)

  {

  	return xt_register_match(&xt_statistic_mt_reg);

  }

  static void __exit statistic_mt_exit(void)

  {

  	xt_unregister_match(&xt_statistic_mt_reg);

  }

  module_init(statistic_mt_init);
  module_exit(statistic_mt_exit);