/*
   * Resizable, Scalable, Concurrent Hash Table
   *

   * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>

   * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>

   * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
   *

   * Code partially derived from nft_hash

   * Rewritten with rehash code from br_multicast plus single list
   * pointer as suggested by Josh Triplett

   *
   * 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.
   */

  #include <linux/atomic.h>

  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/log2.h>

  #include <linux/sched.h>

  #include <linux/rculist.h>

  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <linux/mm.h>

  #include <linux/jhash.h>

  #include <linux/random.h>
  #include <linux/rhashtable.h>

  #include <linux/err.h>

  #include <linux/export.h>

  
  #define HASH_DEFAULT_SIZE	64UL

  #define HASH_MIN_SIZE		4U

  #define BUCKET_LOCKS_PER_CPU	32UL

  union nested_table {
  	union nested_table __rcu *table;
  	struct rhash_head __rcu *bucket;
  };

  static u32 head_hashfn(struct rhashtable *ht,

  		       const struct bucket_table *tbl,
  		       const struct rhash_head *he)

  {

  	return rht_head_hashfn(ht, tbl, he, ht->p);

  }

  #ifdef CONFIG_PROVE_LOCKING

  #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))

  
  int lockdep_rht_mutex_is_held(struct rhashtable *ht)
  {
  	return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
  }
  EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
  
  int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
  {

  	spinlock_t *lock = rht_bucket_lock(tbl, hash);

  
  	return (debug_locks) ? lockdep_is_held(lock) : 1;
  }
  EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
  #else
  #define ASSERT_RHT_MUTEX(HT)

  #endif

  static void nested_table_free(union nested_table *ntbl, unsigned int size)
  {
  	const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
  	const unsigned int len = 1 << shift;
  	unsigned int i;
  
  	ntbl = rcu_dereference_raw(ntbl->table);
  	if (!ntbl)
  		return;
  
  	if (size > len) {
  		size >>= shift;
  		for (i = 0; i < len; i++)
  			nested_table_free(ntbl + i, size);
  	}
  
  	kfree(ntbl);
  }
  
  static void nested_bucket_table_free(const struct bucket_table *tbl)
  {
  	unsigned int size = tbl->size >> tbl->nest;
  	unsigned int len = 1 << tbl->nest;
  	union nested_table *ntbl;
  	unsigned int i;
  
  	ntbl = (union nested_table *)rcu_dereference_raw(tbl->buckets[0]);
  
  	for (i = 0; i < len; i++)
  		nested_table_free(ntbl + i, size);
  
  	kfree(ntbl);
  }

  static void bucket_table_free(const struct bucket_table *tbl)
  {

  	if (tbl->nest)
  		nested_bucket_table_free(tbl);

  	free_bucket_spinlocks(tbl->locks);

  	kvfree(tbl);
  }

  static void bucket_table_free_rcu(struct rcu_head *head)
  {
  	bucket_table_free(container_of(head, struct bucket_table, rcu));
  }

  static union nested_table *nested_table_alloc(struct rhashtable *ht,
  					      union nested_table __rcu **prev,

  					      bool leaf)

  {
  	union nested_table *ntbl;
  	int i;
  
  	ntbl = rcu_dereference(*prev);
  	if (ntbl)
  		return ntbl;
  
  	ntbl = kzalloc(PAGE_SIZE, GFP_ATOMIC);

  	if (ntbl && leaf) {
  		for (i = 0; i < PAGE_SIZE / sizeof(ntbl[0]); i++)

  			INIT_RHT_NULLS_HEAD(ntbl[i].bucket);

  	}
  
  	rcu_assign_pointer(*prev, ntbl);
  
  	return ntbl;
  }
  
  static struct bucket_table *nested_bucket_table_alloc(struct rhashtable *ht,
  						      size_t nbuckets,
  						      gfp_t gfp)
  {
  	const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
  	struct bucket_table *tbl;
  	size_t size;
  
  	if (nbuckets < (1 << (shift + 1)))
  		return NULL;
  
  	size = sizeof(*tbl) + sizeof(tbl->buckets[0]);
  
  	tbl = kzalloc(size, gfp);
  	if (!tbl)
  		return NULL;
  
  	if (!nested_table_alloc(ht, (union nested_table __rcu **)tbl->buckets,

  				false)) {

  		kfree(tbl);
  		return NULL;
  	}
  
  	tbl->nest = (ilog2(nbuckets) - 1) % shift + 1;
  
  	return tbl;
  }

  static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,

  					       size_t nbuckets,
  					       gfp_t gfp)

  {

  	struct bucket_table *tbl = NULL;

  	size_t size, max_locks;

  	int i;

  
  	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);

  	tbl = kvzalloc(size, gfp);

  
  	size = nbuckets;

  	if (tbl == NULL && (gfp & ~__GFP_NOFAIL) != GFP_KERNEL) {

  		tbl = nested_bucket_table_alloc(ht, nbuckets, gfp);
  		nbuckets = 0;
  	}

  	if (tbl == NULL)
  		return NULL;

  	tbl->size = size;

  	max_locks = size >> 1;
  	if (tbl->nest)
  		max_locks = min_t(size_t, max_locks, 1U << tbl->nest);
  
  	if (alloc_bucket_spinlocks(&tbl->locks, &tbl->locks_mask, max_locks,
  				   ht->p.locks_mul, gfp) < 0) {

  		bucket_table_free(tbl);
  		return NULL;
  	}

  	INIT_LIST_HEAD(&tbl->walkers);

  	tbl->hash_rnd = get_random_u32();

  	for (i = 0; i < nbuckets; i++)

  		INIT_RHT_NULLS_HEAD(tbl->buckets[i]);

  	return tbl;

  }

  static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
  						  struct bucket_table *tbl)
  {
  	struct bucket_table *new_tbl;
  
  	do {
  		new_tbl = tbl;
  		tbl = rht_dereference_rcu(tbl->future_tbl, ht);
  	} while (tbl);
  
  	return new_tbl;
  }

  static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)

  {

  	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);

  	struct bucket_table *new_tbl = rhashtable_last_table(ht, old_tbl);

  	struct rhash_head __rcu **pprev = rht_bucket_var(old_tbl, old_hash);
  	int err = -EAGAIN;

  	struct rhash_head *head, *next, *entry;
  	spinlock_t *new_bucket_lock;

  	unsigned int new_hash;

  	if (new_tbl->nest)
  		goto out;
  
  	err = -ENOENT;

  	rht_for_each(entry, old_tbl, old_hash) {
  		err = 0;
  		next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
  
  		if (rht_is_a_nulls(next))
  			break;

  		pprev = &entry->next;
  	}

  	if (err)
  		goto out;

  	new_hash = head_hashfn(ht, new_tbl, entry);

  	new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);

  	spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);

  	head = rht_dereference_bucket(new_tbl->buckets[new_hash],
  				      new_tbl, new_hash);

  	RCU_INIT_POINTER(entry->next, head);

  	rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
  	spin_unlock(new_bucket_lock);

  	rcu_assign_pointer(*pprev, next);

  out:
  	return err;
  }

  static int rhashtable_rehash_chain(struct rhashtable *ht,

  				    unsigned int old_hash)

  {
  	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
  	spinlock_t *old_bucket_lock;

  	int err;

  	old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);

  	spin_lock_bh(old_bucket_lock);

  	while (!(err = rhashtable_rehash_one(ht, old_hash)))

  		;

  
  	if (err == -ENOENT) {
  		old_tbl->rehash++;
  		err = 0;
  	}

  	spin_unlock_bh(old_bucket_lock);

  
  	return err;

  }

  static int rhashtable_rehash_attach(struct rhashtable *ht,
  				    struct bucket_table *old_tbl,
  				    struct bucket_table *new_tbl)

  {

  	/* Make insertions go into the new, empty table right away. Deletions
  	 * and lookups will be attempted in both tables until we synchronize.

  	 * As cmpxchg() provides strong barriers, we do not need
  	 * rcu_assign_pointer().

  	 */

  	if (cmpxchg(&old_tbl->future_tbl, NULL, new_tbl) != NULL)
  		return -EEXIST;

  
  	return 0;
  }
  
  static int rhashtable_rehash_table(struct rhashtable *ht)
  {
  	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
  	struct bucket_table *new_tbl;
  	struct rhashtable_walker *walker;

  	unsigned int old_hash;

  	int err;

  
  	new_tbl = rht_dereference(old_tbl->future_tbl, ht);
  	if (!new_tbl)
  		return 0;

  	for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
  		err = rhashtable_rehash_chain(ht, old_hash);
  		if (err)
  			return err;

  		cond_resched();

  	}

  
  	/* Publish the new table pointer. */
  	rcu_assign_pointer(ht->tbl, new_tbl);

  	spin_lock(&ht->lock);

  	list_for_each_entry(walker, &old_tbl->walkers, list)
  		walker->tbl = NULL;

  	spin_unlock(&ht->lock);

  	/* Wait for readers. All new readers will see the new
  	 * table, and thus no references to the old table will
  	 * remain.
  	 */

  	call_rcu(&old_tbl->rcu, bucket_table_free_rcu);

  
  	return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;

  }

  static int rhashtable_rehash_alloc(struct rhashtable *ht,
  				   struct bucket_table *old_tbl,
  				   unsigned int size)

  {

  	struct bucket_table *new_tbl;

  	int err;

  
  	ASSERT_RHT_MUTEX(ht);

  	new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);

  	if (new_tbl == NULL)
  		return -ENOMEM;

  	err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
  	if (err)
  		bucket_table_free(new_tbl);
  
  	return err;

  }

  
  /**
   * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
   * @ht:		the hash table to shrink

   *

   * This function shrinks the hash table to fit, i.e., the smallest
   * size would not cause it to expand right away automatically.

   *

   * The caller must ensure that no concurrent resizing occurs by holding
   * ht->mutex.
   *

   * The caller must ensure that no concurrent table mutations take place.
   * It is however valid to have concurrent lookups if they are RCU protected.

   *
   * It is valid to have concurrent insertions and deletions protected by per
   * bucket locks or concurrent RCU protected lookups and traversals.

   */

  static int rhashtable_shrink(struct rhashtable *ht)

  {

  	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);

  	unsigned int nelems = atomic_read(&ht->nelems);
  	unsigned int size = 0;

  	if (nelems)
  		size = roundup_pow_of_two(nelems * 3 / 2);

  	if (size < ht->p.min_size)
  		size = ht->p.min_size;
  
  	if (old_tbl->size <= size)
  		return 0;

  	if (rht_dereference(old_tbl->future_tbl, ht))
  		return -EEXIST;

  	return rhashtable_rehash_alloc(ht, old_tbl, size);

  }

  static void rht_deferred_worker(struct work_struct *work)
  {
  	struct rhashtable *ht;
  	struct bucket_table *tbl;

  	int err = 0;

  	ht = container_of(work, struct rhashtable, run_work);

  	mutex_lock(&ht->mutex);

  	tbl = rht_dereference(ht->tbl, ht);

  	tbl = rhashtable_last_table(ht, tbl);

  	if (rht_grow_above_75(ht, tbl))

  		err = rhashtable_rehash_alloc(ht, tbl, tbl->size * 2);

  	else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))

  		err = rhashtable_shrink(ht);
  	else if (tbl->nest)
  		err = rhashtable_rehash_alloc(ht, tbl, tbl->size);

  	if (!err || err == -EEXIST) {
  		int nerr;
  
  		nerr = rhashtable_rehash_table(ht);
  		err = err ?: nerr;
  	}

  	mutex_unlock(&ht->mutex);

  
  	if (err)
  		schedule_work(&ht->run_work);

  }

  static int rhashtable_insert_rehash(struct rhashtable *ht,
  				    struct bucket_table *tbl)

  {
  	struct bucket_table *old_tbl;
  	struct bucket_table *new_tbl;

  	unsigned int size;
  	int err;
  
  	old_tbl = rht_dereference_rcu(ht->tbl, ht);

  
  	size = tbl->size;

  	err = -EBUSY;

  	if (rht_grow_above_75(ht, tbl))
  		size *= 2;

  	/* Do not schedule more than one rehash */
  	else if (old_tbl != tbl)

  		goto fail;
  
  	err = -ENOMEM;

  	new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC | __GFP_NOWARN);

  	if (new_tbl == NULL)
  		goto fail;

  
  	err = rhashtable_rehash_attach(ht, tbl, new_tbl);
  	if (err) {
  		bucket_table_free(new_tbl);
  		if (err == -EEXIST)
  			err = 0;
  	} else
  		schedule_work(&ht->run_work);
  
  	return err;

  
  fail:
  	/* Do not fail the insert if someone else did a rehash. */

  	if (likely(rcu_access_pointer(tbl->future_tbl)))

  		return 0;
  
  	/* Schedule async rehash to retry allocation in process context. */
  	if (err == -ENOMEM)
  		schedule_work(&ht->run_work);
  
  	return err;

  }

  static void *rhashtable_lookup_one(struct rhashtable *ht,
  				   struct bucket_table *tbl, unsigned int hash,
  				   const void *key, struct rhash_head *obj)

  {

  	struct rhashtable_compare_arg arg = {
  		.ht = ht,
  		.key = key,
  	};
  	struct rhash_head __rcu **pprev;

  	struct rhash_head *head;

  	int elasticity;

  	elasticity = RHT_ELASTICITY;

  	pprev = rht_bucket_var(tbl, hash);
  	rht_for_each_continue(head, *pprev, tbl, hash) {

  		struct rhlist_head *list;
  		struct rhlist_head *plist;
  
  		elasticity--;
  		if (!key ||
  		    (ht->p.obj_cmpfn ?
  		     ht->p.obj_cmpfn(&arg, rht_obj(ht, head)) :

  		     rhashtable_compare(&arg, rht_obj(ht, head)))) {
  			pprev = &head->next;

  			continue;

  		}

  
  		if (!ht->rhlist)
  			return rht_obj(ht, head);
  
  		list = container_of(obj, struct rhlist_head, rhead);
  		plist = container_of(head, struct rhlist_head, rhead);
  
  		RCU_INIT_POINTER(list->next, plist);
  		head = rht_dereference_bucket(head->next, tbl, hash);
  		RCU_INIT_POINTER(list->rhead.next, head);
  		rcu_assign_pointer(*pprev, obj);
  
  		return NULL;

  	}

  	if (elasticity <= 0)
  		return ERR_PTR(-EAGAIN);
  
  	return ERR_PTR(-ENOENT);
  }
  
  static struct bucket_table *rhashtable_insert_one(struct rhashtable *ht,
  						  struct bucket_table *tbl,
  						  unsigned int hash,
  						  struct rhash_head *obj,
  						  void *data)
  {

  	struct rhash_head __rcu **pprev;

  	struct bucket_table *new_tbl;
  	struct rhash_head *head;
  
  	if (!IS_ERR_OR_NULL(data))
  		return ERR_PTR(-EEXIST);

  	if (PTR_ERR(data) != -EAGAIN && PTR_ERR(data) != -ENOENT)
  		return ERR_CAST(data);

  	new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);

  	if (new_tbl)
  		return new_tbl;
  
  	if (PTR_ERR(data) != -ENOENT)
  		return ERR_CAST(data);
  
  	if (unlikely(rht_grow_above_max(ht, tbl)))
  		return ERR_PTR(-E2BIG);
  
  	if (unlikely(rht_grow_above_100(ht, tbl)))
  		return ERR_PTR(-EAGAIN);

  	pprev = rht_bucket_insert(ht, tbl, hash);
  	if (!pprev)
  		return ERR_PTR(-ENOMEM);
  
  	head = rht_dereference_bucket(*pprev, tbl, hash);

  
  	RCU_INIT_POINTER(obj->next, head);

  	if (ht->rhlist) {
  		struct rhlist_head *list;
  
  		list = container_of(obj, struct rhlist_head, rhead);
  		RCU_INIT_POINTER(list->next, NULL);
  	}

  	rcu_assign_pointer(*pprev, obj);

  
  	atomic_inc(&ht->nelems);

  	if (rht_grow_above_75(ht, tbl))
  		schedule_work(&ht->run_work);

  	return NULL;
  }

  static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
  				   struct rhash_head *obj)
  {
  	struct bucket_table *new_tbl;
  	struct bucket_table *tbl;
  	unsigned int hash;
  	spinlock_t *lock;
  	void *data;
  
  	tbl = rcu_dereference(ht->tbl);
  
  	/* All insertions must grab the oldest table containing
  	 * the hashed bucket that is yet to be rehashed.
  	 */
  	for (;;) {
  		hash = rht_head_hashfn(ht, tbl, obj, ht->p);
  		lock = rht_bucket_lock(tbl, hash);
  		spin_lock_bh(lock);
  
  		if (tbl->rehash <= hash)
  			break;
  
  		spin_unlock_bh(lock);

  		tbl = rht_dereference_rcu(tbl->future_tbl, ht);

  	}
  
  	data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
  	new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
  	if (PTR_ERR(new_tbl) != -EEXIST)
  		data = ERR_CAST(new_tbl);
  
  	while (!IS_ERR_OR_NULL(new_tbl)) {
  		tbl = new_tbl;
  		hash = rht_head_hashfn(ht, tbl, obj, ht->p);
  		spin_lock_nested(rht_bucket_lock(tbl, hash),
  				 SINGLE_DEPTH_NESTING);
  
  		data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
  		new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
  		if (PTR_ERR(new_tbl) != -EEXIST)
  			data = ERR_CAST(new_tbl);
  
  		spin_unlock(rht_bucket_lock(tbl, hash));
  	}
  
  	spin_unlock_bh(lock);
  
  	if (PTR_ERR(data) == -EAGAIN)
  		data = ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?:
  			       -EAGAIN);
  
  	return data;
  }
  
  void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
  			     struct rhash_head *obj)
  {
  	void *data;
  
  	do {
  		rcu_read_lock();
  		data = rhashtable_try_insert(ht, key, obj);
  		rcu_read_unlock();
  	} while (PTR_ERR(data) == -EAGAIN);
  
  	return data;

  }
  EXPORT_SYMBOL_GPL(rhashtable_insert_slow);

  /**

   * rhashtable_walk_enter - Initialise an iterator

   * @ht:		Table to walk over
   * @iter:	Hash table Iterator
   *
   * This function prepares a hash table walk.
   *
   * Note that if you restart a walk after rhashtable_walk_stop you
   * may see the same object twice.  Also, you may miss objects if
   * there are removals in between rhashtable_walk_stop and the next
   * call to rhashtable_walk_start.
   *
   * For a completely stable walk you should construct your own data
   * structure outside the hash table.
   *

   * This function may be called from any process context, including
   * non-preemptable context, but cannot be called from softirq or
   * hardirq context.

   *

   * You must call rhashtable_walk_exit after this function returns.

   */

  void rhashtable_walk_enter(struct rhashtable *ht, struct rhashtable_iter *iter)

  {
  	iter->ht = ht;
  	iter->p = NULL;
  	iter->slot = 0;
  	iter->skip = 0;

  	iter->end_of_table = 0;

  	spin_lock(&ht->lock);

  	iter->walker.tbl =

  		rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));

  	list_add(&iter->walker.list, &iter->walker.tbl->walkers);

  	spin_unlock(&ht->lock);

  }

  EXPORT_SYMBOL_GPL(rhashtable_walk_enter);

  
  /**
   * rhashtable_walk_exit - Free an iterator
   * @iter:	Hash table Iterator
   *
   * This function frees resources allocated by rhashtable_walk_init.
   */
  void rhashtable_walk_exit(struct rhashtable_iter *iter)
  {

  	spin_lock(&iter->ht->lock);

  	if (iter->walker.tbl)
  		list_del(&iter->walker.list);

  	spin_unlock(&iter->ht->lock);

  }
  EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
  
  /**

   * rhashtable_walk_start_check - Start a hash table walk

   * @iter:	Hash table iterator
   *

   * Start a hash table walk at the current iterator position.  Note that we take
   * the RCU lock in all cases including when we return an error.  So you must
   * always call rhashtable_walk_stop to clean up.

   *
   * Returns zero if successful.
   *
   * Returns -EAGAIN if resize event occured.  Note that the iterator
   * will rewind back to the beginning and you may use it immediately
   * by calling rhashtable_walk_next.

   *
   * rhashtable_walk_start is defined as an inline variant that returns
   * void. This is preferred in cases where the caller would ignore
   * resize events and always continue.

   */

  int rhashtable_walk_start_check(struct rhashtable_iter *iter)

  	__acquires(RCU)

  {

  	struct rhashtable *ht = iter->ht;

  	bool rhlist = ht->rhlist;

  	rcu_read_lock();

  	spin_lock(&ht->lock);

  	if (iter->walker.tbl)
  		list_del(&iter->walker.list);

  	spin_unlock(&ht->lock);

  	if (iter->end_of_table)
  		return 0;
  	if (!iter->walker.tbl) {

  		iter->walker.tbl = rht_dereference_rcu(ht->tbl, ht);

  		iter->slot = 0;
  		iter->skip = 0;

  		return -EAGAIN;
  	}

  	if (iter->p && !rhlist) {
  		/*
  		 * We need to validate that 'p' is still in the table, and
  		 * if so, update 'skip'
  		 */
  		struct rhash_head *p;
  		int skip = 0;
  		rht_for_each_rcu(p, iter->walker.tbl, iter->slot) {
  			skip++;
  			if (p == iter->p) {
  				iter->skip = skip;
  				goto found;
  			}
  		}
  		iter->p = NULL;
  	} else if (iter->p && rhlist) {
  		/* Need to validate that 'list' is still in the table, and
  		 * if so, update 'skip' and 'p'.
  		 */
  		struct rhash_head *p;
  		struct rhlist_head *list;
  		int skip = 0;
  		rht_for_each_rcu(p, iter->walker.tbl, iter->slot) {
  			for (list = container_of(p, struct rhlist_head, rhead);
  			     list;
  			     list = rcu_dereference(list->next)) {
  				skip++;
  				if (list == iter->list) {
  					iter->p = p;

  					iter->skip = skip;

  					goto found;
  				}
  			}
  		}
  		iter->p = NULL;
  	}
  found:

  	return 0;
  }

  EXPORT_SYMBOL_GPL(rhashtable_walk_start_check);

  
  /**

   * __rhashtable_walk_find_next - Find the next element in a table (or the first
   * one in case of a new walk).
   *

   * @iter:	Hash table iterator
   *

   * Returns the found object or NULL when the end of the table is reached.

   *

   * Returns -EAGAIN if resize event occurred.

   */

  static void *__rhashtable_walk_find_next(struct rhashtable_iter *iter)

  {

  	struct bucket_table *tbl = iter->walker.tbl;

  	struct rhlist_head *list = iter->list;

  	struct rhashtable *ht = iter->ht;
  	struct rhash_head *p = iter->p;

  	bool rhlist = ht->rhlist;

  	if (!tbl)
  		return NULL;

  
  	for (; iter->slot < tbl->size; iter->slot++) {
  		int skip = iter->skip;
  
  		rht_for_each_rcu(p, tbl, iter->slot) {

  			if (rhlist) {
  				list = container_of(p, struct rhlist_head,
  						    rhead);
  				do {
  					if (!skip)
  						goto next;
  					skip--;
  					list = rcu_dereference(list->next);
  				} while (list);
  
  				continue;
  			}

  			if (!skip)
  				break;
  			skip--;
  		}
  
  next:
  		if (!rht_is_a_nulls(p)) {
  			iter->skip++;
  			iter->p = p;

  			iter->list = list;
  			return rht_obj(ht, rhlist ? &list->rhead : p);

  		}
  
  		iter->skip = 0;
  	}

  	iter->p = NULL;

  	/* Ensure we see any new tables. */
  	smp_rmb();

  	iter->walker.tbl = rht_dereference_rcu(tbl->future_tbl, ht);
  	if (iter->walker.tbl) {

  		iter->slot = 0;
  		iter->skip = 0;

  		return ERR_PTR(-EAGAIN);

  	} else {
  		iter->end_of_table = true;

  	}

  	return NULL;

  }

  
  /**
   * rhashtable_walk_next - Return the next object and advance the iterator
   * @iter:	Hash table iterator
   *
   * Note that you must call rhashtable_walk_stop when you are finished
   * with the walk.
   *
   * Returns the next object or NULL when the end of the table is reached.
   *
   * Returns -EAGAIN if resize event occurred.  Note that the iterator
   * will rewind back to the beginning and you may continue to use it.
   */
  void *rhashtable_walk_next(struct rhashtable_iter *iter)
  {
  	struct rhlist_head *list = iter->list;
  	struct rhashtable *ht = iter->ht;
  	struct rhash_head *p = iter->p;
  	bool rhlist = ht->rhlist;
  
  	if (p) {
  		if (!rhlist || !(list = rcu_dereference(list->next))) {
  			p = rcu_dereference(p->next);
  			list = container_of(p, struct rhlist_head, rhead);
  		}
  		if (!rht_is_a_nulls(p)) {
  			iter->skip++;
  			iter->p = p;
  			iter->list = list;
  			return rht_obj(ht, rhlist ? &list->rhead : p);
  		}
  
  		/* At the end of this slot, switch to next one and then find
  		 * next entry from that point.
  		 */
  		iter->skip = 0;
  		iter->slot++;
  	}
  
  	return __rhashtable_walk_find_next(iter);
  }

  EXPORT_SYMBOL_GPL(rhashtable_walk_next);
  
  /**

   * rhashtable_walk_peek - Return the next object but don't advance the iterator
   * @iter:	Hash table iterator
   *
   * Returns the next object or NULL when the end of the table is reached.
   *
   * Returns -EAGAIN if resize event occurred.  Note that the iterator
   * will rewind back to the beginning and you may continue to use it.
   */
  void *rhashtable_walk_peek(struct rhashtable_iter *iter)
  {
  	struct rhlist_head *list = iter->list;
  	struct rhashtable *ht = iter->ht;
  	struct rhash_head *p = iter->p;
  
  	if (p)
  		return rht_obj(ht, ht->rhlist ? &list->rhead : p);
  
  	/* No object found in current iter, find next one in the table. */
  
  	if (iter->skip) {
  		/* A nonzero skip value points to the next entry in the table
  		 * beyond that last one that was found. Decrement skip so
  		 * we find the current value. __rhashtable_walk_find_next
  		 * will restore the original value of skip assuming that
  		 * the table hasn't changed.
  		 */
  		iter->skip--;
  	}
  
  	return __rhashtable_walk_find_next(iter);
  }
  EXPORT_SYMBOL_GPL(rhashtable_walk_peek);
  
  /**

   * rhashtable_walk_stop - Finish a hash table walk
   * @iter:	Hash table iterator
   *

   * Finish a hash table walk.  Does not reset the iterator to the start of the
   * hash table.

   */
  void rhashtable_walk_stop(struct rhashtable_iter *iter)

  	__releases(RCU)

  {

  	struct rhashtable *ht;

  	struct bucket_table *tbl = iter->walker.tbl;

  	if (!tbl)

  		goto out;

  
  	ht = iter->ht;

  	spin_lock(&ht->lock);

  	if (tbl->rehash < tbl->size)

  		list_add(&iter->walker.list, &tbl->walkers);

  	else

  		iter->walker.tbl = NULL;

  	spin_unlock(&ht->lock);

  out:
  	rcu_read_unlock();

  }
  EXPORT_SYMBOL_GPL(rhashtable_walk_stop);

  static size_t rounded_hashtable_size(const struct rhashtable_params *params)

  {

  	size_t retsize;
  
  	if (params->nelem_hint)
  		retsize = max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
  			      (unsigned long)params->min_size);
  	else
  		retsize = max(HASH_DEFAULT_SIZE,
  			      (unsigned long)params->min_size);
  
  	return retsize;

  }

  static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
  {
  	return jhash2(key, length, seed);
  }

  /**
   * rhashtable_init - initialize a new hash table
   * @ht:		hash table to be initialized
   * @params:	configuration parameters
   *
   * Initializes a new hash table based on the provided configuration
   * parameters. A table can be configured either with a variable or
   * fixed length key:
   *
   * Configuration Example 1: Fixed length keys
   * struct test_obj {
   *	int			key;
   *	void *			my_member;
   *	struct rhash_head	node;
   * };
   *
   * struct rhashtable_params params = {
   *	.head_offset = offsetof(struct test_obj, node),
   *	.key_offset = offsetof(struct test_obj, key),
   *	.key_len = sizeof(int),

   *	.hashfn = jhash,

   * };
   *
   * Configuration Example 2: Variable length keys
   * struct test_obj {
   *	[...]
   *	struct rhash_head	node;
   * };
   *

   * u32 my_hash_fn(const void *data, u32 len, u32 seed)

   * {
   *	struct test_obj *obj = data;
   *
   *	return [... hash ...];
   * }
   *
   * struct rhashtable_params params = {
   *	.head_offset = offsetof(struct test_obj, node),

   *	.hashfn = jhash,

   *	.obj_hashfn = my_hash_fn,

   * };
   */

  int rhashtable_init(struct rhashtable *ht,
  		    const struct rhashtable_params *params)

  {
  	struct bucket_table *tbl;
  	size_t size;

  	if ((!params->key_len && !params->obj_hashfn) ||

  	    (params->obj_hashfn && !params->obj_cmpfn))

  		return -EINVAL;

  	memset(ht, 0, sizeof(*ht));
  	mutex_init(&ht->mutex);

  	spin_lock_init(&ht->lock);

  	memcpy(&ht->p, params, sizeof(*params));

  	if (params->min_size)
  		ht->p.min_size = roundup_pow_of_two(params->min_size);

  	/* Cap total entries at 2^31 to avoid nelems overflow. */
  	ht->max_elems = 1u << 31;

  
  	if (params->max_size) {
  		ht->p.max_size = rounddown_pow_of_two(params->max_size);
  		if (ht->p.max_size < ht->max_elems / 2)
  			ht->max_elems = ht->p.max_size * 2;
  	}

  	ht->p.min_size = max_t(u16, ht->p.min_size, HASH_MIN_SIZE);

  	size = rounded_hashtable_size(&ht->p);

  	if (params->locks_mul)
  		ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
  	else
  		ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;

  	ht->key_len = ht->p.key_len;
  	if (!params->hashfn) {
  		ht->p.hashfn = jhash;
  
  		if (!(ht->key_len & (sizeof(u32) - 1))) {
  			ht->key_len /= sizeof(u32);
  			ht->p.hashfn = rhashtable_jhash2;
  		}
  	}

  	/*
  	 * This is api initialization and thus we need to guarantee the
  	 * initial rhashtable allocation. Upon failure, retry with the
  	 * smallest possible size with __GFP_NOFAIL semantics.
  	 */

  	tbl = bucket_table_alloc(ht, size, GFP_KERNEL);

  	if (unlikely(tbl == NULL)) {
  		size = max_t(u16, ht->p.min_size, HASH_MIN_SIZE);
  		tbl = bucket_table_alloc(ht, size, GFP_KERNEL | __GFP_NOFAIL);
  	}

  	atomic_set(&ht->nelems, 0);

  	RCU_INIT_POINTER(ht->tbl, tbl);

  	INIT_WORK(&ht->run_work, rht_deferred_worker);

  	return 0;
  }
  EXPORT_SYMBOL_GPL(rhashtable_init);
  
  /**

   * rhltable_init - initialize a new hash list table
   * @hlt:	hash list table to be initialized
   * @params:	configuration parameters
   *
   * Initializes a new hash list table.
   *
   * See documentation for rhashtable_init.
   */
  int rhltable_init(struct rhltable *hlt, const struct rhashtable_params *params)
  {
  	int err;

  	err = rhashtable_init(&hlt->ht, params);
  	hlt->ht.rhlist = true;
  	return err;
  }
  EXPORT_SYMBOL_GPL(rhltable_init);
  
  static void rhashtable_free_one(struct rhashtable *ht, struct rhash_head *obj,
  				void (*free_fn)(void *ptr, void *arg),
  				void *arg)
  {
  	struct rhlist_head *list;
  
  	if (!ht->rhlist) {
  		free_fn(rht_obj(ht, obj), arg);
  		return;
  	}
  
  	list = container_of(obj, struct rhlist_head, rhead);
  	do {
  		obj = &list->rhead;
  		list = rht_dereference(list->next, ht);
  		free_fn(rht_obj(ht, obj), arg);
  	} while (list);
  }
  
  /**

   * rhashtable_free_and_destroy - free elements and destroy hash table

   * @ht:		the hash table to destroy

   * @free_fn:	callback to release resources of element
   * @arg:	pointer passed to free_fn

   *

   * Stops an eventual async resize. If defined, invokes free_fn for each
   * element to releasal resources. Please note that RCU protected
   * readers may still be accessing the elements. Releasing of resources
   * must occur in a compatible manner. Then frees the bucket array.
   *
   * This function will eventually sleep to wait for an async resize
   * to complete. The caller is responsible that no further write operations
   * occurs in parallel.

   */

  void rhashtable_free_and_destroy(struct rhashtable *ht,
  				 void (*free_fn)(void *ptr, void *arg),
  				 void *arg)

  {

  	struct bucket_table *tbl, *next_tbl;

  	unsigned int i;

  	cancel_work_sync(&ht->run_work);

  	mutex_lock(&ht->mutex);

  	tbl = rht_dereference(ht->tbl, ht);

  restart:

  	if (free_fn) {
  		for (i = 0; i < tbl->size; i++) {
  			struct rhash_head *pos, *next;

  			cond_resched();

  			for (pos = rht_dereference(*rht_bucket(tbl, i), ht),

  			     next = !rht_is_a_nulls(pos) ?
  					rht_dereference(pos->next, ht) : NULL;
  			     !rht_is_a_nulls(pos);
  			     pos = next,
  			     next = !rht_is_a_nulls(pos) ?
  					rht_dereference(pos->next, ht) : NULL)

  				rhashtable_free_one(ht, pos, free_fn, arg);

  		}
  	}

  	next_tbl = rht_dereference(tbl->future_tbl, ht);

  	bucket_table_free(tbl);

  	if (next_tbl) {
  		tbl = next_tbl;
  		goto restart;
  	}

  	mutex_unlock(&ht->mutex);

  }

  EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
  
  void rhashtable_destroy(struct rhashtable *ht)
  {
  	return rhashtable_free_and_destroy(ht, NULL, NULL);
  }

  EXPORT_SYMBOL_GPL(rhashtable_destroy);

  
  struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
  					    unsigned int hash)
  {
  	const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
  	static struct rhash_head __rcu *rhnull =
  		(struct rhash_head __rcu *)NULLS_MARKER(0);
  	unsigned int index = hash & ((1 << tbl->nest) - 1);
  	unsigned int size = tbl->size >> tbl->nest;
  	unsigned int subhash = hash;
  	union nested_table *ntbl;
  
  	ntbl = (union nested_table *)rcu_dereference_raw(tbl->buckets[0]);

  	ntbl = rht_dereference_bucket_rcu(ntbl[index].table, tbl, hash);

  	subhash >>= tbl->nest;
  
  	while (ntbl && size > (1 << shift)) {
  		index = subhash & ((1 << shift) - 1);

  		ntbl = rht_dereference_bucket_rcu(ntbl[index].table,
  						  tbl, hash);

  		size >>= shift;
  		subhash >>= shift;
  	}
  
  	if (!ntbl)
  		return &rhnull;
  
  	return &ntbl[subhash].bucket;
  
  }
  EXPORT_SYMBOL_GPL(rht_bucket_nested);
  
  struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
  						   struct bucket_table *tbl,
  						   unsigned int hash)
  {
  	const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
  	unsigned int index = hash & ((1 << tbl->nest) - 1);
  	unsigned int size = tbl->size >> tbl->nest;
  	union nested_table *ntbl;

  
  	ntbl = (union nested_table *)rcu_dereference_raw(tbl->buckets[0]);
  	hash >>= tbl->nest;

  	ntbl = nested_table_alloc(ht, &ntbl[index].table,

  				  size <= (1 << shift));

  
  	while (ntbl && size > (1 << shift)) {
  		index = hash & ((1 << shift) - 1);
  		size >>= shift;
  		hash >>= shift;

  		ntbl = nested_table_alloc(ht, &ntbl[index].table,

  					  size <= (1 << shift));

  	}
  
  	if (!ntbl)
  		return NULL;
  
  	return &ntbl[hash].bucket;
  
  }
  EXPORT_SYMBOL_GPL(rht_bucket_nested_insert);