/*
   * 2002-10-18  written by Jim Houston jim.houston@ccur.com
   *	Copyright (C) 2002 by Concurrent Computer Corporation
   *	Distributed under the GNU GPL license version 2.
   *
   * Modified by George Anzinger to reuse immediately and to use
   * find bit instructions.  Also removed _irq on spinlocks.
   *

   * Modified by Nadia Derbey to make it RCU safe.
   *

   * Small id to pointer translation service.

   *

   * It uses a radix tree like structure as a sparse array indexed

   * by the id to obtain the pointer.  The bitmap makes allocating

   * a new id quick.

   *
   * You call it to allocate an id (an int) an associate with that id a
   * pointer or what ever, we treat it as a (void *).  You can pass this
   * id to a user for him to pass back at a later time.  You then pass
   * that id to this code and it returns your pointer.

   * You can release ids at any time. When all ids are released, most of

   * the memory is returned (we keep IDR_FREE_MAX) in a local pool so we

   * don't need to go to the memory "store" during an id allocate, just

   * so you don't need to be too concerned about locking and conflicts
   * with the slab allocator.
   */
  
  #ifndef TEST                        // to test in user space...
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #endif

  #include <linux/err.h>

  #include <linux/string.h>
  #include <linux/idr.h>

  #include <linux/spinlock.h>

  static struct kmem_cache *idr_layer_cache;

  static DEFINE_SPINLOCK(simple_ida_lock);

  static struct idr_layer *get_from_free_list(struct idr *idp)

  {
  	struct idr_layer *p;

  	unsigned long flags;

  	spin_lock_irqsave(&idp->lock, flags);

  	if ((p = idp->id_free)) {
  		idp->id_free = p->ary[0];
  		idp->id_free_cnt--;
  		p->ary[0] = NULL;
  	}

  	spin_unlock_irqrestore(&idp->lock, flags);

  	return(p);
  }

  static void idr_layer_rcu_free(struct rcu_head *head)
  {
  	struct idr_layer *layer;
  
  	layer = container_of(head, struct idr_layer, rcu_head);
  	kmem_cache_free(idr_layer_cache, layer);
  }
  
  static inline void free_layer(struct idr_layer *p)
  {
  	call_rcu(&p->rcu_head, idr_layer_rcu_free);
  }

  /* only called when idp->lock is held */

  static void __move_to_free_list(struct idr *idp, struct idr_layer *p)

  {
  	p->ary[0] = idp->id_free;
  	idp->id_free = p;
  	idp->id_free_cnt++;
  }

  static void move_to_free_list(struct idr *idp, struct idr_layer *p)

  {

  	unsigned long flags;

  	/*
  	 * Depends on the return element being zeroed.
  	 */

  	spin_lock_irqsave(&idp->lock, flags);

  	__move_to_free_list(idp, p);

  	spin_unlock_irqrestore(&idp->lock, flags);

  }

  static void idr_mark_full(struct idr_layer **pa, int id)
  {
  	struct idr_layer *p = pa[0];
  	int l = 0;
  
  	__set_bit(id & IDR_MASK, &p->bitmap);
  	/*
  	 * If this layer is full mark the bit in the layer above to
  	 * show that this part of the radix tree is full.  This may
  	 * complete the layer above and require walking up the radix
  	 * tree.
  	 */
  	while (p->bitmap == IDR_FULL) {
  		if (!(p = pa[++l]))
  			break;
  		id = id >> IDR_BITS;
  		__set_bit((id & IDR_MASK), &p->bitmap);
  	}
  }

  /**

   * idr_pre_get - reserve resources for idr allocation

   * @idp:	idr handle
   * @gfp_mask:	memory allocation flags
   *

   * This function should be called prior to calling the idr_get_new* functions.
   * It preallocates enough memory to satisfy the worst possible allocation. The
   * caller should pass in GFP_KERNEL if possible.  This of course requires that
   * no spinning locks be held.

   *

   * If the system is REALLY out of memory this function returns %0,
   * otherwise %1.

   */

  int idr_pre_get(struct idr *idp, gfp_t gfp_mask)

  {
  	while (idp->id_free_cnt < IDR_FREE_MAX) {
  		struct idr_layer *new;

  		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);

  		if (new == NULL)

  			return (0);

  		move_to_free_list(idp, new);

  	}
  	return 1;
  }
  EXPORT_SYMBOL(idr_pre_get);

  static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)

  {
  	int n, m, sh;
  	struct idr_layer *p, *new;

  	int l, id, oid;

  	unsigned long bm;

  
  	id = *starting_id;

   restart:

  	p = idp->top;
  	l = idp->layers;
  	pa[l--] = NULL;
  	while (1) {
  		/*
  		 * We run around this while until we reach the leaf node...
  		 */
  		n = (id >> (IDR_BITS*l)) & IDR_MASK;
  		bm = ~p->bitmap;
  		m = find_next_bit(&bm, IDR_SIZE, n);
  		if (m == IDR_SIZE) {
  			/* no space available go back to previous layer. */
  			l++;

  			oid = id;

  			id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;

  
  			/* if already at the top layer, we need to grow */

  			if (id >= 1 << (idp->layers * IDR_BITS)) {

  				*starting_id = id;

  				return IDR_NEED_TO_GROW;

  			}

  			p = pa[l];
  			BUG_ON(!p);

  
  			/* If we need to go up one layer, continue the
  			 * loop; otherwise, restart from the top.
  			 */
  			sh = IDR_BITS * (l + 1);
  			if (oid >> sh == id >> sh)
  				continue;
  			else
  				goto restart;

  		}
  		if (m != n) {
  			sh = IDR_BITS*l;
  			id = ((id >> sh) ^ n ^ m) << sh;
  		}
  		if ((id >= MAX_ID_BIT) || (id < 0))

  			return IDR_NOMORE_SPACE;

  		if (l == 0)
  			break;
  		/*
  		 * Create the layer below if it is missing.
  		 */
  		if (!p->ary[m]) {

  			new = get_from_free_list(idp);
  			if (!new)

  				return -1;

  			new->layer = l-1;

  			rcu_assign_pointer(p->ary[m], new);

  			p->count++;
  		}
  		pa[l--] = p;
  		p = p->ary[m];
  	}

  
  	pa[l] = p;
  	return id;

  }

  static int idr_get_empty_slot(struct idr *idp, int starting_id,
  			      struct idr_layer **pa)

  {
  	struct idr_layer *p, *new;
  	int layers, v, id;

  	unsigned long flags;

  	id = starting_id;
  build_up:
  	p = idp->top;
  	layers = idp->layers;
  	if (unlikely(!p)) {

  		if (!(p = get_from_free_list(idp)))

  			return -1;

  		p->layer = 0;

  		layers = 1;
  	}
  	/*
  	 * Add a new layer to the top of the tree if the requested
  	 * id is larger than the currently allocated space.
  	 */

  	while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {

  		layers++;

  		if (!p->count) {
  			/* special case: if the tree is currently empty,
  			 * then we grow the tree by moving the top node
  			 * upwards.
  			 */
  			p->layer++;

  			continue;

  		}

  		if (!(new = get_from_free_list(idp))) {

  			/*
  			 * The allocation failed.  If we built part of
  			 * the structure tear it down.
  			 */

  			spin_lock_irqsave(&idp->lock, flags);

  			for (new = p; p && p != idp->top; new = p) {
  				p = p->ary[0];
  				new->ary[0] = NULL;
  				new->bitmap = new->count = 0;

  				__move_to_free_list(idp, new);

  			}

  			spin_unlock_irqrestore(&idp->lock, flags);

  			return -1;
  		}
  		new->ary[0] = p;
  		new->count = 1;

  		new->layer = layers-1;

  		if (p->bitmap == IDR_FULL)
  			__set_bit(0, &new->bitmap);
  		p = new;
  	}

  	rcu_assign_pointer(idp->top, p);

  	idp->layers = layers;

  	v = sub_alloc(idp, &id, pa);

  	if (v == IDR_NEED_TO_GROW)

  		goto build_up;
  	return(v);
  }

  static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
  {
  	struct idr_layer *pa[MAX_LEVEL];
  	int id;
  
  	id = idr_get_empty_slot(idp, starting_id, pa);
  	if (id >= 0) {
  		/*
  		 * Successfully found an empty slot.  Install the user
  		 * pointer and mark the slot full.
  		 */

  		rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],
  				(struct idr_layer *)ptr);

  		pa[0]->count++;
  		idr_mark_full(pa, id);
  	}
  
  	return id;
  }

  /**

   * idr_get_new_above - allocate new idr entry above or equal to a start id

   * @idp: idr handle

   * @ptr: pointer you want associated with the id

   * @starting_id: id to start search at

   * @id: pointer to the allocated handle
   *
   * This is the allocate id function.  It should be called with any
   * required locks.
   *

   * If allocation from IDR's private freelist fails, idr_get_new_above() will

   * return %-EAGAIN.  The caller should retry the idr_pre_get() call to refill

   * IDR's preallocation and then retry the idr_get_new_above() call.
   *

   * If the idr is full idr_get_new_above() will return %-ENOSPC.

   *

   * @id returns a value in the range @starting_id ... %0x7fffffff

   */
  int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
  {
  	int rv;

  	rv = idr_get_new_above_int(idp, ptr, starting_id);
  	/*
  	 * This is a cheap hack until the IDR code can be fixed to
  	 * return proper error values.
  	 */

  	if (rv < 0)
  		return _idr_rc_to_errno(rv);

  	*id = rv;
  	return 0;
  }
  EXPORT_SYMBOL(idr_get_new_above);
  
  /**
   * idr_get_new - allocate new idr entry
   * @idp: idr handle

   * @ptr: pointer you want associated with the id

   * @id: pointer to the allocated handle
   *

   * If allocation from IDR's private freelist fails, idr_get_new_above() will

   * return %-EAGAIN.  The caller should retry the idr_pre_get() call to refill

   * IDR's preallocation and then retry the idr_get_new_above() call.

   *

   * If the idr is full idr_get_new_above() will return %-ENOSPC.

   *

   * @id returns a value in the range %0 ... %0x7fffffff

   */
  int idr_get_new(struct idr *idp, void *ptr, int *id)
  {
  	int rv;

  	rv = idr_get_new_above_int(idp, ptr, 0);
  	/*
  	 * This is a cheap hack until the IDR code can be fixed to
  	 * return proper error values.
  	 */

  	if (rv < 0)
  		return _idr_rc_to_errno(rv);

  	*id = rv;
  	return 0;
  }
  EXPORT_SYMBOL(idr_get_new);
  
  static void idr_remove_warning(int id)
  {

  	printk(KERN_WARNING
  		"idr_remove called for id=%d which is not allocated.
  ", id);

  	dump_stack();
  }
  
  static void sub_remove(struct idr *idp, int shift, int id)
  {
  	struct idr_layer *p = idp->top;
  	struct idr_layer **pa[MAX_LEVEL];
  	struct idr_layer ***paa = &pa[0];

  	struct idr_layer *to_free;

  	int n;
  
  	*paa = NULL;
  	*++paa = &idp->top;
  
  	while ((shift > 0) && p) {
  		n = (id >> shift) & IDR_MASK;
  		__clear_bit(n, &p->bitmap);
  		*++paa = &p->ary[n];
  		p = p->ary[n];
  		shift -= IDR_BITS;
  	}
  	n = id & IDR_MASK;
  	if (likely(p != NULL && test_bit(n, &p->bitmap))){
  		__clear_bit(n, &p->bitmap);

  		rcu_assign_pointer(p->ary[n], NULL);
  		to_free = NULL;

  		while(*paa && ! --((**paa)->count)){

  			if (to_free)
  				free_layer(to_free);
  			to_free = **paa;

  			**paa-- = NULL;
  		}

  		if (!*paa)

  			idp->layers = 0;

  		if (to_free)
  			free_layer(to_free);

  	} else

  		idr_remove_warning(id);

  }
  
  /**

   * idr_remove - remove the given id and free its slot

   * @idp: idr handle
   * @id: unique key

   */
  void idr_remove(struct idr *idp, int id)
  {
  	struct idr_layer *p;

  	struct idr_layer *to_free;

  
  	/* Mask off upper bits we don't use for the search. */
  	id &= MAX_ID_MASK;
  
  	sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);

  	if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&

  	    idp->top->ary[0]) {
  		/*
  		 * Single child at leftmost slot: we can shrink the tree.
  		 * This level is not needed anymore since when layers are
  		 * inserted, they are inserted at the top of the existing
  		 * tree.
  		 */
  		to_free = idp->top;

  		p = idp->top->ary[0];

  		rcu_assign_pointer(idp->top, p);

  		--idp->layers;

  		to_free->bitmap = to_free->count = 0;
  		free_layer(to_free);

  	}
  	while (idp->id_free_cnt >= IDR_FREE_MAX) {

  		p = get_from_free_list(idp);

  		/*
  		 * Note: we don't call the rcu callback here, since the only
  		 * layers that fall into the freelist are those that have been
  		 * preallocated.
  		 */

  		kmem_cache_free(idr_layer_cache, p);

  	}

  	return;

  }
  EXPORT_SYMBOL(idr_remove);
  
  /**

   * idr_remove_all - remove all ids from the given idr tree
   * @idp: idr handle
   *
   * idr_destroy() only frees up unused, cached idp_layers, but this
   * function will remove all id mappings and leave all idp_layers
   * unused.
   *

   * A typical clean-up sequence for objects stored in an idr tree will

   * use idr_for_each() to free all objects, if necessay, then
   * idr_remove_all() to remove all ids, and idr_destroy() to free
   * up the cached idr_layers.
   */
  void idr_remove_all(struct idr *idp)
  {

  	int n, id, max;

  	int bt_mask;

  	struct idr_layer *p;
  	struct idr_layer *pa[MAX_LEVEL];
  	struct idr_layer **paa = &pa[0];
  
  	n = idp->layers * IDR_BITS;
  	p = idp->top;

  	rcu_assign_pointer(idp->top, NULL);

  	max = 1 << n;
  
  	id = 0;

  	while (id < max) {

  		while (n > IDR_BITS && p) {
  			n -= IDR_BITS;
  			*paa++ = p;
  			p = p->ary[(id >> n) & IDR_MASK];
  		}

  		bt_mask = id;

  		id += 1 << n;

  		/* Get the highest bit that the above add changed from 0->1. */
  		while (n < fls(id ^ bt_mask)) {

  			if (p)
  				free_layer(p);

  			n += IDR_BITS;
  			p = *--paa;
  		}
  	}

  	idp->layers = 0;
  }
  EXPORT_SYMBOL(idr_remove_all);
  
  /**

   * idr_destroy - release all cached layers within an idr tree

   * @idp: idr handle

   */
  void idr_destroy(struct idr *idp)
  {
  	while (idp->id_free_cnt) {

  		struct idr_layer *p = get_from_free_list(idp);

  		kmem_cache_free(idr_layer_cache, p);
  	}
  }
  EXPORT_SYMBOL(idr_destroy);
  
  /**

   * idr_find - return pointer for given id
   * @idp: idr handle
   * @id: lookup key
   *
   * Return the pointer given the id it has been registered with.  A %NULL
   * return indicates that @id is not valid or you passed %NULL in
   * idr_get_new().
   *

   * This function can be called under rcu_read_lock(), given that the leaf
   * pointers lifetimes are correctly managed.

   */
  void *idr_find(struct idr *idp, int id)
  {
  	int n;
  	struct idr_layer *p;

  	p = rcu_dereference_raw(idp->top);

  	if (!p)
  		return NULL;
  	n = (p->layer+1) * IDR_BITS;

  
  	/* Mask off upper bits we don't use for the search. */
  	id &= MAX_ID_MASK;
  
  	if (id >= (1 << n))
  		return NULL;

  	BUG_ON(n == 0);

  
  	while (n > 0 && p) {
  		n -= IDR_BITS;

  		BUG_ON(n != p->layer*IDR_BITS);

  		p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  	}
  	return((void *)p);
  }
  EXPORT_SYMBOL(idr_find);

  /**

   * idr_for_each - iterate through all stored pointers
   * @idp: idr handle
   * @fn: function to be called for each pointer
   * @data: data passed back to callback function
   *
   * Iterate over the pointers registered with the given idr.  The
   * callback function will be called for each pointer currently
   * registered, passing the id, the pointer and the data pointer passed
   * to this function.  It is not safe to modify the idr tree while in
   * the callback, so functions such as idr_get_new and idr_remove are
   * not allowed.
   *
   * We check the return of @fn each time. If it returns anything other

   * than %0, we break out and return that value.

   *
   * The caller must serialize idr_for_each() vs idr_get_new() and idr_remove().
   */
  int idr_for_each(struct idr *idp,
  		 int (*fn)(int id, void *p, void *data), void *data)
  {
  	int n, id, max, error = 0;
  	struct idr_layer *p;
  	struct idr_layer *pa[MAX_LEVEL];
  	struct idr_layer **paa = &pa[0];
  
  	n = idp->layers * IDR_BITS;

  	p = rcu_dereference_raw(idp->top);

  	max = 1 << n;
  
  	id = 0;
  	while (id < max) {
  		while (n > 0 && p) {
  			n -= IDR_BITS;
  			*paa++ = p;

  			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  		}
  
  		if (p) {
  			error = fn(id, (void *)p, data);
  			if (error)
  				break;
  		}
  
  		id += 1 << n;
  		while (n < fls(id)) {
  			n += IDR_BITS;
  			p = *--paa;
  		}
  	}
  
  	return error;
  }
  EXPORT_SYMBOL(idr_for_each);
  
  /**

   * idr_get_next - lookup next object of id to given id.
   * @idp: idr handle

   * @nextidp:  pointer to lookup key

   *
   * Returns pointer to registered object with id, which is next number to

   * given id. After being looked up, *@nextidp will be updated for the next
   * iteration.

   */
  
  void *idr_get_next(struct idr *idp, int *nextidp)
  {
  	struct idr_layer *p, *pa[MAX_LEVEL];
  	struct idr_layer **paa = &pa[0];
  	int id = *nextidp;
  	int n, max;
  
  	/* find first ent */
  	n = idp->layers * IDR_BITS;
  	max = 1 << n;

  	p = rcu_dereference_raw(idp->top);

  	if (!p)
  		return NULL;
  
  	while (id < max) {
  		while (n > 0 && p) {
  			n -= IDR_BITS;
  			*paa++ = p;

  			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  		}
  
  		if (p) {
  			*nextidp = id;
  			return p;
  		}
  
  		id += 1 << n;
  		while (n < fls(id)) {
  			n += IDR_BITS;
  			p = *--paa;
  		}
  	}
  	return NULL;
  }

  EXPORT_SYMBOL(idr_get_next);

  
  
  /**

   * idr_replace - replace pointer for given id
   * @idp: idr handle
   * @ptr: pointer you want associated with the id
   * @id: lookup key
   *
   * Replace the pointer registered with an id and return the old value.

   * A %-ENOENT return indicates that @id was not found.
   * A %-EINVAL return indicates that @id was not within valid constraints.

   *

   * The caller must serialize with writers.

   */
  void *idr_replace(struct idr *idp, void *ptr, int id)
  {
  	int n;
  	struct idr_layer *p, *old_p;

  	p = idp->top;

  	if (!p)
  		return ERR_PTR(-EINVAL);
  
  	n = (p->layer+1) * IDR_BITS;

  
  	id &= MAX_ID_MASK;
  
  	if (id >= (1 << n))
  		return ERR_PTR(-EINVAL);
  
  	n -= IDR_BITS;
  	while ((n > 0) && p) {
  		p = p->ary[(id >> n) & IDR_MASK];
  		n -= IDR_BITS;
  	}
  
  	n = id & IDR_MASK;
  	if (unlikely(p == NULL || !test_bit(n, &p->bitmap)))
  		return ERR_PTR(-ENOENT);
  
  	old_p = p->ary[n];

  	rcu_assign_pointer(p->ary[n], ptr);

  
  	return old_p;
  }
  EXPORT_SYMBOL(idr_replace);

  void __init idr_init_cache(void)

  {

  	idr_layer_cache = kmem_cache_create("idr_layer_cache",

  				sizeof(struct idr_layer), 0, SLAB_PANIC, NULL);

  }
  
  /**
   * idr_init - initialize idr handle
   * @idp:	idr handle
   *
   * This function is use to set up the handle (@idp) that you will pass
   * to the rest of the functions.
   */
  void idr_init(struct idr *idp)
  {

  	memset(idp, 0, sizeof(struct idr));
  	spin_lock_init(&idp->lock);
  }
  EXPORT_SYMBOL(idr_init);

  /**
   * DOC: IDA description

   * IDA - IDR based ID allocator
   *

   * This is id allocator without id -> pointer translation.  Memory

   * usage is much lower than full blown idr because each id only
   * occupies a bit.  ida uses a custom leaf node which contains
   * IDA_BITMAP_BITS slots.
   *
   * 2007-04-25  written by Tejun Heo <htejun@gmail.com>
   */
  
  static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)
  {
  	unsigned long flags;
  
  	if (!ida->free_bitmap) {
  		spin_lock_irqsave(&ida->idr.lock, flags);
  		if (!ida->free_bitmap) {
  			ida->free_bitmap = bitmap;
  			bitmap = NULL;
  		}
  		spin_unlock_irqrestore(&ida->idr.lock, flags);
  	}
  
  	kfree(bitmap);
  }
  
  /**
   * ida_pre_get - reserve resources for ida allocation
   * @ida:	ida handle
   * @gfp_mask:	memory allocation flag
   *
   * This function should be called prior to locking and calling the
   * following function.  It preallocates enough memory to satisfy the
   * worst possible allocation.
   *

   * If the system is REALLY out of memory this function returns %0,
   * otherwise %1.

   */
  int ida_pre_get(struct ida *ida, gfp_t gfp_mask)
  {
  	/* allocate idr_layers */
  	if (!idr_pre_get(&ida->idr, gfp_mask))
  		return 0;
  
  	/* allocate free_bitmap */
  	if (!ida->free_bitmap) {
  		struct ida_bitmap *bitmap;
  
  		bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);
  		if (!bitmap)
  			return 0;
  
  		free_bitmap(ida, bitmap);
  	}
  
  	return 1;
  }
  EXPORT_SYMBOL(ida_pre_get);
  
  /**
   * ida_get_new_above - allocate new ID above or equal to a start id
   * @ida:	ida handle

   * @starting_id: id to start search at

   * @p_id:	pointer to the allocated handle
   *

   * Allocate new ID above or equal to @starting_id.  It should be called
   * with any required locks.

   *

   * If memory is required, it will return %-EAGAIN, you should unlock

   * and go back to the ida_pre_get() call.  If the ida is full, it will

   * return %-ENOSPC.

   *

   * @p_id returns a value in the range @starting_id ... %0x7fffffff.

   */
  int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
  {
  	struct idr_layer *pa[MAX_LEVEL];
  	struct ida_bitmap *bitmap;
  	unsigned long flags;
  	int idr_id = starting_id / IDA_BITMAP_BITS;
  	int offset = starting_id % IDA_BITMAP_BITS;
  	int t, id;
  
   restart:
  	/* get vacant slot */
  	t = idr_get_empty_slot(&ida->idr, idr_id, pa);

  	if (t < 0)
  		return _idr_rc_to_errno(t);

  
  	if (t * IDA_BITMAP_BITS >= MAX_ID_BIT)
  		return -ENOSPC;
  
  	if (t != idr_id)
  		offset = 0;
  	idr_id = t;
  
  	/* if bitmap isn't there, create a new one */
  	bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];
  	if (!bitmap) {
  		spin_lock_irqsave(&ida->idr.lock, flags);
  		bitmap = ida->free_bitmap;
  		ida->free_bitmap = NULL;
  		spin_unlock_irqrestore(&ida->idr.lock, flags);
  
  		if (!bitmap)
  			return -EAGAIN;
  
  		memset(bitmap, 0, sizeof(struct ida_bitmap));

  		rcu_assign_pointer(pa[0]->ary[idr_id & IDR_MASK],
  				(void *)bitmap);

  		pa[0]->count++;
  	}
  
  	/* lookup for empty slot */
  	t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);
  	if (t == IDA_BITMAP_BITS) {
  		/* no empty slot after offset, continue to the next chunk */
  		idr_id++;
  		offset = 0;
  		goto restart;
  	}
  
  	id = idr_id * IDA_BITMAP_BITS + t;
  	if (id >= MAX_ID_BIT)
  		return -ENOSPC;
  
  	__set_bit(t, bitmap->bitmap);
  	if (++bitmap->nr_busy == IDA_BITMAP_BITS)
  		idr_mark_full(pa, idr_id);
  
  	*p_id = id;
  
  	/* Each leaf node can handle nearly a thousand slots and the
  	 * whole idea of ida is to have small memory foot print.
  	 * Throw away extra resources one by one after each successful
  	 * allocation.
  	 */
  	if (ida->idr.id_free_cnt || ida->free_bitmap) {

  		struct idr_layer *p = get_from_free_list(&ida->idr);

  		if (p)
  			kmem_cache_free(idr_layer_cache, p);
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(ida_get_new_above);
  
  /**
   * ida_get_new - allocate new ID
   * @ida:	idr handle
   * @p_id:	pointer to the allocated handle
   *
   * Allocate new ID.  It should be called with any required locks.
   *

   * If memory is required, it will return %-EAGAIN, you should unlock

   * and go back to the idr_pre_get() call.  If the idr is full, it will

   * return %-ENOSPC.

   *

   * @p_id returns a value in the range %0 ... %0x7fffffff.

   */
  int ida_get_new(struct ida *ida, int *p_id)
  {
  	return ida_get_new_above(ida, 0, p_id);
  }
  EXPORT_SYMBOL(ida_get_new);
  
  /**
   * ida_remove - remove the given ID
   * @ida:	ida handle
   * @id:		ID to free
   */
  void ida_remove(struct ida *ida, int id)
  {
  	struct idr_layer *p = ida->idr.top;
  	int shift = (ida->idr.layers - 1) * IDR_BITS;
  	int idr_id = id / IDA_BITMAP_BITS;
  	int offset = id % IDA_BITMAP_BITS;
  	int n;
  	struct ida_bitmap *bitmap;
  
  	/* clear full bits while looking up the leaf idr_layer */
  	while ((shift > 0) && p) {
  		n = (idr_id >> shift) & IDR_MASK;
  		__clear_bit(n, &p->bitmap);
  		p = p->ary[n];
  		shift -= IDR_BITS;
  	}
  
  	if (p == NULL)
  		goto err;
  
  	n = idr_id & IDR_MASK;
  	__clear_bit(n, &p->bitmap);
  
  	bitmap = (void *)p->ary[n];
  	if (!test_bit(offset, bitmap->bitmap))
  		goto err;
  
  	/* update bitmap and remove it if empty */
  	__clear_bit(offset, bitmap->bitmap);
  	if (--bitmap->nr_busy == 0) {
  		__set_bit(n, &p->bitmap);	/* to please idr_remove() */
  		idr_remove(&ida->idr, idr_id);
  		free_bitmap(ida, bitmap);
  	}
  
  	return;
  
   err:
  	printk(KERN_WARNING
  	       "ida_remove called for id=%d which is not allocated.
  ", id);
  }
  EXPORT_SYMBOL(ida_remove);
  
  /**
   * ida_destroy - release all cached layers within an ida tree

   * @ida:		ida handle

   */
  void ida_destroy(struct ida *ida)
  {
  	idr_destroy(&ida->idr);
  	kfree(ida->free_bitmap);
  }
  EXPORT_SYMBOL(ida_destroy);
  
  /**

   * ida_simple_get - get a new id.
   * @ida: the (initialized) ida.
   * @start: the minimum id (inclusive, < 0x8000000)
   * @end: the maximum id (exclusive, < 0x8000000 or 0)
   * @gfp_mask: memory allocation flags
   *
   * Allocates an id in the range start <= id < end, or returns -ENOSPC.
   * On memory allocation failure, returns -ENOMEM.
   *
   * Use ida_simple_remove() to get rid of an id.
   */
  int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
  		   gfp_t gfp_mask)
  {
  	int ret, id;
  	unsigned int max;

  	unsigned long flags;

  
  	BUG_ON((int)start < 0);
  	BUG_ON((int)end < 0);
  
  	if (end == 0)
  		max = 0x80000000;
  	else {
  		BUG_ON(end < start);
  		max = end - 1;
  	}
  
  again:
  	if (!ida_pre_get(ida, gfp_mask))
  		return -ENOMEM;

  	spin_lock_irqsave(&simple_ida_lock, flags);

  	ret = ida_get_new_above(ida, start, &id);
  	if (!ret) {
  		if (id > max) {
  			ida_remove(ida, id);
  			ret = -ENOSPC;
  		} else {
  			ret = id;
  		}
  	}

  	spin_unlock_irqrestore(&simple_ida_lock, flags);

  
  	if (unlikely(ret == -EAGAIN))
  		goto again;
  
  	return ret;
  }
  EXPORT_SYMBOL(ida_simple_get);
  
  /**
   * ida_simple_remove - remove an allocated id.
   * @ida: the (initialized) ida.
   * @id: the id returned by ida_simple_get.
   */
  void ida_simple_remove(struct ida *ida, unsigned int id)
  {

  	unsigned long flags;

  	BUG_ON((int)id < 0);

  	spin_lock_irqsave(&simple_ida_lock, flags);

  	ida_remove(ida, id);

  	spin_unlock_irqrestore(&simple_ida_lock, flags);

  }
  EXPORT_SYMBOL(ida_simple_remove);
  
  /**

   * ida_init - initialize ida handle
   * @ida:	ida handle
   *
   * This function is use to set up the handle (@ida) that you will pass
   * to the rest of the functions.
   */
  void ida_init(struct ida *ida)
  {
  	memset(ida, 0, sizeof(struct ida));
  	idr_init(&ida->idr);
  
  }
  EXPORT_SYMBOL(ida_init);