/* iptables match extension to limit the number of packets per second
 * seperately for each hashbucket (sourceip/sourceport/dstip/dstport)
 *
 * (C) 2003-2004 by Harald Welte <laforge@netfilter.org>
 *
 * $Id: ipt_hashlimit.c 3244 2004-10-20 16:24:29Z laforge@netfilter.org $
 *
 * Development of this code was funded by Astaro AG, http://www.astaro.com/
 */
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/list.h>
#include <linux/skbuff.h>
#include <linux/mm.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <net/net_namespace.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/xt_hashlimit.h>
#include <linux/mutex.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("iptables match for limiting per hash-bucket");
MODULE_ALIAS("ipt_hashlimit");
MODULE_ALIAS("ip6t_hashlimit");

/* need to declare this at the top */
static struct proc_dir_entry *hashlimit_procdir4;
static struct proc_dir_entry *hashlimit_procdir6;
static const struct file_operations dl_file_ops;

/* hash table crap */
struct dsthash_dst {
        union {
                struct {
                        __be32 src;
                        __be32 dst;
                } ip;
                struct {
                        __be32 src[4];
                        __be32 dst[4];
                } ip6;
        } addr;
        __be16 src_port;
        __be16 dst_port;
};

struct dsthash_ent {
        /* static / read-only parts in the beginning */
        struct hlist_node node;
        struct dsthash_dst dst;

        /* modified structure members in the end */
        unsigned long expires;          /* precalculated expiry time */
        struct {
                unsigned long prev;     /* last modification */
                u_int32_t credit;
                u_int32_t credit_cap, cost;
        } rateinfo;
};

struct xt_hashlimit_htable {
        struct hlist_node node;         /* global list of all htables */
        atomic_t use;
        int family;

        struct hashlimit_cfg cfg;       /* config */

        /* used internally */
        spinlock_t lock;                /* lock for list_head */
        u_int32_t rnd;                  /* random seed for hash */
        int rnd_initialized;
        unsigned int count;             /* number entries in table */
        struct timer_list timer;        /* timer for gc */

        /* seq_file stuff */
        struct proc_dir_entry *pde;

        struct hlist_head hash[0];      /* hashtable itself */
};

static DEFINE_SPINLOCK(hashlimit_lock); /* protects htables list */
static DEFINE_MUTEX(hlimit_mutex);      /* additional checkentry protection */
static HLIST_HEAD(hashlimit_htables);
static struct kmem_cache *hashlimit_cachep __read_mostly;

static inline bool dst_cmp(const struct dsthash_ent *ent,
                           const struct dsthash_dst *b)
{
        return !memcmp(&ent->dst, b, sizeof(ent->dst));
}

static u_int32_t
hash_dst(const struct xt_hashlimit_htable *ht, const struct dsthash_dst *dst)
{
        return jhash(dst, sizeof(*dst), ht->rnd) % ht->cfg.size;
}

static struct dsthash_ent *
dsthash_find(const struct xt_hashlimit_htable *ht,
             const struct dsthash_dst *dst)
{
        struct dsthash_ent *ent;
        struct hlist_node *pos;
        u_int32_t hash = hash_dst(ht, dst);

        if (!hlist_empty(&ht->hash[hash])) {
                hlist_for_each_entry(ent, pos, &ht->hash[hash], node)
                        if (dst_cmp(ent, dst))
                                return ent;
        }
        return NULL;
}

/* allocate dsthash_ent, initialize dst, put in htable and lock it */
static struct dsthash_ent *
dsthash_alloc_init(struct xt_hashlimit_htable *ht,
                   const struct dsthash_dst *dst)
{
        struct dsthash_ent *ent;

        /* initialize hash with random val at the time we allocate
         * the first hashtable entry */
        if (!ht->rnd_initialized) {
                get_random_bytes(&ht->rnd, 4);
                ht->rnd_initialized = 1;
        }

        if (ht->cfg.max && ht->count >= ht->cfg.max) {
                /* FIXME: do something. question is what.. */
                if (net_ratelimit())
                        printk(KERN_WARNING
                                "xt_hashlimit: max count of %u reached\n",
                                ht->cfg.max);
                return NULL;
        }

        ent = kmem_cache_alloc(hashlimit_cachep, GFP_ATOMIC);
        if (!ent) {
                if (net_ratelimit())
                        printk(KERN_ERR
                                "xt_hashlimit: can't allocate dsthash_ent\n");
                return NULL;
        }
        memcpy(&ent->dst, dst, sizeof(ent->dst));

        hlist_add_head(&ent->node, &ht->hash[hash_dst(ht, dst)]);
        ht->count++;
        return ent;
}

static inline void
dsthash_free(struct xt_hashlimit_htable *ht, struct dsthash_ent *ent)
{
        hlist_del(&ent->node);
        kmem_cache_free(hashlimit_cachep, ent);
        ht->count--;
}
static void htable_gc(unsigned long htlong);

static int htable_create(struct xt_hashlimit_info *minfo, int family)
{
        struct xt_hashlimit_htable *hinfo;
        unsigned int size;
        unsigned int i;

        if (minfo->cfg.size)
                size = minfo->cfg.size;
        else {
                size = ((num_physpages << PAGE_SHIFT) / 16384) /
                       sizeof(struct list_head);
                if (num_physpages > (1024 * 1024 * 1024 / PAGE_SIZE))
                        size = 8192;
                if (size < 16)
                        size = 16;
        }
        /* FIXME: don't use vmalloc() here or anywhere else -HW */
        hinfo = vmalloc(sizeof(struct xt_hashlimit_htable) +
                        sizeof(struct list_head) * size);
        if (!hinfo) {
                printk(KERN_ERR "xt_hashlimit: unable to create hashtable\n");
                return -1;
        }
        minfo->hinfo = hinfo;

        /* copy match config into hashtable config */
        memcpy(&hinfo->cfg, &minfo->cfg, sizeof(hinfo->cfg));
        hinfo->cfg.size = size;
        if (!hinfo->cfg.max)
                hinfo->cfg.max = 8 * hinfo->cfg.size;
        else if (hinfo->cfg.max < hinfo->cfg.size)
                hinfo->cfg.max = hinfo->cfg.size;

        for (i = 0; i < hinfo->cfg.size; i++)
                INIT_HLIST_HEAD(&hinfo->hash[i]);

        atomic_set(&hinfo->use, 1);
        hinfo->count = 0;
        hinfo->family = family;
        hinfo->rnd_initialized = 0;
        spin_lock_init(&hinfo->lock);
        hinfo->pde = create_proc_entry(minfo->name, 0,
                                       family == AF_INET ? hashlimit_procdir4 :
                                                           hashlimit_procdir6);
        if (!hinfo->pde) {
                vfree(hinfo);
                return -1;
        }
        hinfo->pde->proc_fops = &dl_file_ops;
        hinfo->pde->data = hinfo;

        setup_timer(&hinfo->timer, htable_gc, (unsigned long )hinfo);
        hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);
        add_timer(&hinfo->timer);

        spin_lock_bh(&hashlimit_lock);
        hlist_add_head(&hinfo->node, &hashlimit_htables);
        spin_unlock_bh(&hashlimit_lock);

        return 0;
}

static bool select_all(const struct xt_hashlimit_htable *ht,
                       const struct dsthash_ent *he)
{
        return 1;
}

static bool select_gc(const struct xt_hashlimit_htable *ht,
                      const struct dsthash_ent *he)
{
        return time_after_eq(jiffies, he->expires);
}

static void htable_selective_cleanup(struct xt_hashlimit_htable *ht,
                        bool (*select)(const struct xt_hashlimit_htable *ht,
                                      const struct dsthash_ent *he))
{
        unsigned int i;

        /* lock hash table and iterate over it */
        spin_lock_bh(&ht->lock);
        for (i = 0; i < ht->cfg.size; i++) {
                struct dsthash_ent *dh;
                struct hlist_node *pos, *n;
                hlist_for_each_entry_safe(dh, pos, n, &ht->hash[i], node) {
                        if ((*select)(ht, dh))
                                dsthash_free(ht, dh);
                }
        }
        spin_unlock_bh(&ht->lock);
}

/* hash table garbage collector, run by timer */
static void htable_gc(unsigned long htlong)
{
        struct xt_hashlimit_htable *ht = (struct xt_hashlimit_htable *)htlong;

        htable_selective_cleanup(ht, select_gc);

        /* re-add the timer accordingly */
        ht->timer.expires = jiffies + msecs_to_jiffies(ht->cfg.gc_interval);
        add_timer(&ht->timer);
}

static void htable_destroy(struct xt_hashlimit_htable *hinfo)
{
        /* remove timer, if it is pending */
        if (timer_pending(&hinfo->timer))
                del_timer(&hinfo->timer);

        /* remove proc entry */
        remove_proc_entry(hinfo->pde->name,
                          hinfo->family == AF_INET ? hashlimit_procdir4 :
                                                     hashlimit_procdir6);
        htable_selective_cleanup(hinfo, select_all);
        vfree(hinfo);
}

static struct xt_hashlimit_htable *htable_find_get(const char *name,
                                                   int family)
{
        struct xt_hashlimit_htable *hinfo;
        struct hlist_node *pos;

        spin_lock_bh(&hashlimit_lock);
        hlist_for_each_entry(hinfo, pos, &hashlimit_htables, node) {
                if (!strcmp(name, hinfo->pde->name) &&
                    hinfo->family == family) {
                        atomic_inc(&hinfo->use);
                        spin_unlock_bh(&hashlimit_lock);
                        return hinfo;
                }
        }
        spin_unlock_bh(&hashlimit_lock);
        return NULL;
}

static void htable_put(struct xt_hashlimit_htable *hinfo)
{
        if (atomic_dec_and_test(&hinfo->use)) {
                spin_lock_bh(&hashlimit_lock);
                hlist_del(&hinfo->node);
                spin_unlock_bh(&hashlimit_lock);
                htable_destroy(hinfo);
        }
}

/* The algorithm used is the Simple Token Bucket Filter (TBF)
 * see net/sched/sch_tbf.c in the linux source tree
 */

/* Rusty: This is my (non-mathematically-inclined) understanding of
   this algorithm.  The `average rate' in jiffies becomes your initial
   amount of credit `credit' and the most credit you can ever have
   `credit_cap'.  The `peak rate' becomes the cost of passing the
   test, `cost'.

   `prev' tracks the last packet hit: you gain one credit per jiffy.
   If you get credit balance more than this, the extra credit is
   discarded.  Every time the match passes, you lose `cost' credits;
   if you don't have that many, the test fails.

   See Alexey's formal explanation in net/sched/sch_tbf.c.

   To get the maximum range, we multiply by this factor (ie. you get N
   credits per jiffy).  We want to allow a rate as low as 1 per day
   (slowest userspace tool allows), which means
   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32 ie.
*/
#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))

/* Repeated shift and or gives us all 1s, final shift and add 1 gives
 * us the power of 2 below the theoretical max, so GCC simply does a
 * shift. */
#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)

#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)

/* Precision saver. */
static inline u_int32_t
user2credits(u_int32_t user)
{
        /* If multiplying would overflow... */
        if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
                /* Divide first. */
                return (user / XT_HASHLIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;

        return (user * HZ * CREDITS_PER_JIFFY) / XT_HASHLIMIT_SCALE;
}

static inline void rateinfo_recalc(struct dsthash_ent *dh, unsigned long now)
{
        dh->rateinfo.credit += (now - dh->rateinfo.prev) * CREDITS_PER_JIFFY;
        if (dh->rateinfo.credit > dh->rateinfo.credit_cap)
                dh->rateinfo.credit = dh->rateinfo.credit_cap;
        dh->rateinfo.prev = now;
}

static int
hashlimit_init_dst(const struct xt_hashlimit_htable *hinfo,
                   struct dsthash_dst *dst,
                   const struct sk_buff *skb, unsigned int protoff)
{
        __be16 _ports[2], *ports;
        int nexthdr;

        memset(dst, 0, sizeof(*dst));

        switch (hinfo->family) {
        case AF_INET:
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DIP)
                        dst->addr.ip.dst = ip_hdr(skb)->daddr;
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SIP)
                        dst->addr.ip.src = ip_hdr(skb)->saddr;

                if (!(hinfo->cfg.mode &
                      (XT_HASHLIMIT_HASH_DPT | XT_HASHLIMIT_HASH_SPT)))
                        return 0;
                nexthdr = ip_hdr(skb)->protocol;
                break;
#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
        case AF_INET6:
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DIP)
                        memcpy(&dst->addr.ip6.dst, &ipv6_hdr(skb)->daddr,
                               sizeof(dst->addr.ip6.dst));
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SIP)
                        memcpy(&dst->addr.ip6.src, &ipv6_hdr(skb)->saddr,
                               sizeof(dst->addr.ip6.src));

                if (!(hinfo->cfg.mode &
                      (XT_HASHLIMIT_HASH_DPT | XT_HASHLIMIT_HASH_SPT)))
                        return 0;
                nexthdr = ipv6_find_hdr(skb, &protoff, -1, NULL);
                if (nexthdr < 0)
                        return -1;
                break;
#endif
        default:
                BUG();
                return 0;
        }

        switch (nexthdr) {
        case IPPROTO_TCP:
        case IPPROTO_UDP:
        case IPPROTO_UDPLITE:
        case IPPROTO_SCTP:
        case IPPROTO_DCCP:
                ports = skb_header_pointer(skb, protoff, sizeof(_ports),
                                           &_ports);
                break;
        default:
                _ports[0] = _ports[1] = 0;
                ports = _ports;
                break;
        }
        if (!ports)
                return -1;
        if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SPT)
                dst->src_port = ports[0];
        if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DPT)
                dst->dst_port = ports[1];
        return 0;
}

static bool
hashlimit_match(const struct sk_buff *skb,
                const struct net_device *in,
                const struct net_device *out,
                const struct xt_match *match,
                const void *matchinfo,
                int offset,
                unsigned int protoff,
                bool *hotdrop)
{
        const struct xt_hashlimit_info *r =
                ((const struct xt_hashlimit_info *)matchinfo)->u.master;
        struct xt_hashlimit_htable *hinfo = r->hinfo;
        unsigned long now = jiffies;
        struct dsthash_ent *dh;
        struct dsthash_dst dst;

        if (hashlimit_init_dst(hinfo, &dst, skb, protoff) < 0)
                goto hotdrop;

        spin_lock_bh(&hinfo->lock);
        dh = dsthash_find(hinfo, &dst);
        if (!dh) {
                dh = dsthash_alloc_init(hinfo, &dst);
                if (!dh) {
                        spin_unlock_bh(&hinfo->lock);
                        goto hotdrop;
                }

                dh->expires = jiffies + msecs_to_jiffies(hinfo->cfg.expire);
                dh->rateinfo.prev = jiffies;
                dh->rateinfo.credit = user2credits(hinfo->cfg.avg *
                                                   hinfo->cfg.burst);
                dh->rateinfo.credit_cap = user2credits(hinfo->cfg.avg *
                                                       hinfo->cfg.burst);
                dh->rateinfo.cost = user2credits(hinfo->cfg.avg);
        } else {
                /* update expiration timeout */
                dh->expires = now + msecs_to_jiffies(hinfo->cfg.expire);
                rateinfo_recalc(dh, now);
        }

        if (dh->rateinfo.credit >= dh->rateinfo.cost) {
                /* We're underlimit. */
                dh->rateinfo.credit -= dh->rateinfo.cost;
                spin_unlock_bh(&hinfo->lock);
                return true;
        }

        spin_unlock_bh(&hinfo->lock);

        /* default case: we're overlimit, thus don't match */
        return false;

hotdrop:
        *hotdrop = true;
        return false;
}

static bool
hashlimit_checkentry(const char *tablename,
                     const void *inf,
                     const struct xt_match *match,
                     void *matchinfo,
                     unsigned int hook_mask)
{
        struct xt_hashlimit_info *r = matchinfo;

        /* Check for overflow. */
        if (r->cfg.burst == 0 ||
            user2credits(r->cfg.avg * r->cfg.burst) < user2credits(r->cfg.avg)) {
                printk(KERN_ERR "xt_hashlimit: overflow, try lower: %u/%u\n",
                       r->cfg.avg, r->cfg.burst);
                return false;
        }
        if (r->cfg.mode == 0 ||
            r->cfg.mode > (XT_HASHLIMIT_HASH_DPT |
                           XT_HASHLIMIT_HASH_DIP |
                           XT_HASHLIMIT_HASH_SIP |
                           XT_HASHLIMIT_HASH_SPT))
                return false;
        if (!r->cfg.gc_interval)
                return false;
        if (!r->cfg.expire)
                return false;
        if (r->name[sizeof(r->name) - 1] != '\0')
                return false;

        /* This is the best we've got: We cannot release and re-grab lock,
         * since checkentry() is called before x_tables.c grabs xt_mutex.
         * We also cannot grab the hashtable spinlock, since htable_create will
         * call vmalloc, and that can sleep.  And we cannot just re-search
         * the list of htable's in htable_create(), since then we would
         * create duplicate proc files. -HW */
        mutex_lock(&hlimit_mutex);
        r->hinfo = htable_find_get(r->name, match->family);
        if (!r->hinfo && htable_create(r, match->family) != 0) {
                mutex_unlock(&hlimit_mutex);
                return false;
        }
        mutex_unlock(&hlimit_mutex);

        /* Ugly hack: For SMP, we only want to use one set */
        r->u.master = r;
        return true;
}

static void
hashlimit_destroy(const struct xt_match *match, void *matchinfo)
{
        const struct xt_hashlimit_info *r = matchinfo;

        htable_put(r->hinfo);
}

#ifdef CONFIG_COMPAT
struct compat_xt_hashlimit_info {
        char name[IFNAMSIZ];
        struct hashlimit_cfg cfg;
        compat_uptr_t hinfo;
        compat_uptr_t master;
};

static void compat_from_user(void *dst, void *src)
{
        int off = offsetof(struct compat_xt_hashlimit_info, hinfo);

        memcpy(dst, src, off);
        memset(dst + off, 0, sizeof(struct compat_xt_hashlimit_info) - off);
}

static int compat_to_user(void __user *dst, void *src)
{
        int off = offsetof(struct compat_xt_hashlimit_info, hinfo);

        return copy_to_user(dst, src, off) ? -EFAULT : 0;
}
#endif

static struct xt_match xt_hashlimit[] __read_mostly = {
        {
                .name           = "hashlimit",
                .family         = AF_INET,
                .match          = hashlimit_match,
                .matchsize      = sizeof(struct xt_hashlimit_info),
#ifdef CONFIG_COMPAT
                .compatsize     = sizeof(struct compat_xt_hashlimit_info),
                .compat_from_user = compat_from_user,
                .compat_to_user = compat_to_user,
#endif
                .checkentry     = hashlimit_checkentry,
                .destroy        = hashlimit_destroy,
                .me             = THIS_MODULE
        },
        {
                .name           = "hashlimit",
                .family         = AF_INET6,
                .match          = hashlimit_match,
                .matchsize      = sizeof(struct xt_hashlimit_info),
#ifdef CONFIG_COMPAT
                .compatsize     = sizeof(struct compat_xt_hashlimit_info),
                .compat_from_user = compat_from_user,
                .compat_to_user = compat_to_user,
#endif
                .checkentry     = hashlimit_checkentry,
                .destroy        = hashlimit_destroy,
                .me             = THIS_MODULE
        },
};

/* PROC stuff */
static void *dl_seq_start(struct seq_file *s, loff_t *pos)
{
        struct proc_dir_entry *pde = s->private;
        struct xt_hashlimit_htable *htable = pde->data;
        unsigned int *bucket;

        spin_lock_bh(&htable->lock);
        if (*pos >= htable->cfg.size)
                return NULL;

        bucket = kmalloc(sizeof(unsigned int), GFP_ATOMIC);
        if (!bucket)
                return ERR_PTR(-ENOMEM);

        *bucket = *pos;
        return bucket;
}

static void *dl_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
        struct proc_dir_entry *pde = s->private;
        struct xt_hashlimit_htable *htable = pde->data;
        unsigned int *bucket = (unsigned int *)v;

        *pos = ++(*bucket);
        if (*pos >= htable->cfg.size) {
                kfree(v);
                return NULL;
        }
        return bucket;
}

static void dl_seq_stop(struct seq_file *s, void *v)
{
        struct proc_dir_entry *pde = s->private;
        struct xt_hashlimit_htable *htable = pde->data;
        unsigned int *bucket = (unsigned int *)v;

        kfree(bucket);
        spin_unlock_bh(&htable->lock);
}

static int dl_seq_real_show(struct dsthash_ent *ent, int family,
                                   struct seq_file *s)
{
        /* recalculate to show accurate numbers */
        rateinfo_recalc(ent, jiffies);

        switch (family) {
        case AF_INET:
                return seq_printf(s, "%ld %u.%u.%u.%u:%u->"
                                     "%u.%u.%u.%u:%u %u %u %u\n",
                                 (long)(ent->expires - jiffies)/HZ,
                                 NIPQUAD(ent->dst.addr.ip.src),
                                 ntohs(ent->dst.src_port),
                                 NIPQUAD(ent->dst.addr.ip.dst),
                                 ntohs(ent->dst.dst_port),
                                 ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                 ent->rateinfo.cost);
        case AF_INET6:
                return seq_printf(s, "%ld " NIP6_FMT ":%u->"
                                     NIP6_FMT ":%u %u %u %u\n",
                                 (long)(ent->expires - jiffies)/HZ,
                                 NIP6(*(struct in6_addr *)&ent->dst.addr.ip6.src),
                                 ntohs(ent->dst.src_port),
                                 NIP6(*(struct in6_addr *)&ent->dst.addr.ip6.dst),
                                 ntohs(ent->dst.dst_port),
                                 ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                 ent->rateinfo.cost);
        default:
                BUG();
                return 0;
        }
}

static int dl_seq_show(struct seq_file *s, void *v)
{
        struct proc_dir_entry *pde = s->private;
        struct xt_hashlimit_htable *htable = pde->data;
        unsigned int *bucket = (unsigned int *)v;
        struct dsthash_ent *ent;
        struct hlist_node *pos;

        if (!hlist_empty(&htable->hash[*bucket])) {
                hlist_for_each_entry(ent, pos, &htable->hash[*bucket], node)
                        if (dl_seq_real_show(ent, htable->family, s))
                                return 1;
        }
        return 0;
}

static const struct seq_operations dl_seq_ops = {
        .start = dl_seq_start,
        .next  = dl_seq_next,
        .stop  = dl_seq_stop,
        .show  = dl_seq_show
};

static int dl_proc_open(struct inode *inode, struct file *file)
{
        int ret = seq_open(file, &dl_seq_ops);

        if (!ret) {
                struct seq_file *sf = file->private_data;
                sf->private = PDE(inode);
        }
        return ret;
}

static const struct file_operations dl_file_ops = {
        .owner   = THIS_MODULE,
        .open    = dl_proc_open,
        .read    = seq_read,
        .llseek  = seq_lseek,
        .release = seq_release
};

static int __init xt_hashlimit_init(void)
{
        int err;

        err = xt_register_matches(xt_hashlimit, ARRAY_SIZE(xt_hashlimit));
        if (err < 0)
                goto err1;

        err = -ENOMEM;
        hashlimit_cachep = kmem_cache_create("xt_hashlimit",
                                            sizeof(struct dsthash_ent), 0, 0,
                                            NULL);
        if (!hashlimit_cachep) {
                printk(KERN_ERR "xt_hashlimit: unable to create slab cache\n");
                goto err2;
        }
        hashlimit_procdir4 = proc_mkdir("ipt_hashlimit", init_net.proc_net);
        if (!hashlimit_procdir4) {
                printk(KERN_ERR "xt_hashlimit: unable to create proc dir "
                                "entry\n");
                goto err3;
        }
        hashlimit_procdir6 = proc_mkdir("ip6t_hashlimit", init_net.proc_net);
        if (!hashlimit_procdir6) {
                printk(KERN_ERR "xt_hashlimit: unable to create proc dir "
                                "entry\n");
                goto err4;
        }
        return 0;
err4:
        remove_proc_entry("ipt_hashlimit", init_net.proc_net);
err3:
        kmem_cache_destroy(hashlimit_cachep);
err2:
        xt_unregister_matches(xt_hashlimit, ARRAY_SIZE(xt_hashlimit));
err1:
        return err;

}

static void __exit xt_hashlimit_fini(void)
{
        remove_proc_entry("ipt_hashlimit", init_net.proc_net);
        remove_proc_entry("ip6t_hashlimit", init_net.proc_net);
        kmem_cache_destroy(hashlimit_cachep);
        xt_unregister_matches(xt_hashlimit, ARRAY_SIZE(xt_hashlimit));
}

module_init(xt_hashlimit_init);
module_exit(xt_hashlimit_fini);