#include <linux/bitmap.h>

  #include <linux/export.h>

  #include <linux/idr.h>

  #include <linux/slab.h>

  #include <linux/spinlock.h>

  DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);

  static DEFINE_SPINLOCK(simple_ida_lock);

  int idr_alloc_cmn(struct idr *idr, void *ptr, unsigned long *index,
  		  unsigned long start, unsigned long end, gfp_t gfp,
  		  bool ext)

  {

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
  		return -EINVAL;

  	radix_tree_iter_init(&iter, start);

  	if (ext)
  		slot = idr_get_free_ext(&idr->idr_rt, &iter, gfp, end);
  	else
  		slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);

  	if (IS_ERR(slot))
  		return PTR_ERR(slot);

  	radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
  	radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);

  
  	if (index)
  		*index = iter.index;
  	return 0;

  }

  EXPORT_SYMBOL_GPL(idr_alloc_cmn);

  /**
   * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion

   * @idr: idr handle

   * @ptr: pointer to be associated with the new id
   * @start: the minimum id (inclusive)

   * @end: the maximum id (exclusive)
   * @gfp: memory allocation flags

   *

   * Allocates an ID larger than the last ID allocated if one is available.
   * If not, it will attempt to allocate the smallest ID that is larger or
   * equal to @start.

   */

  int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)

  {

  	int id, curr = idr->idr_next;

  	if (curr < start)
  		curr = start;

  	id = idr_alloc(idr, ptr, curr, end, gfp);
  	if ((id == -ENOSPC) && (curr > start))
  		id = idr_alloc(idr, ptr, start, curr, gfp);

  	if (id >= 0)
  		idr->idr_next = id + 1U;

  	return id;

  }

  EXPORT_SYMBOL(idr_alloc_cyclic);

  /**

   * idr_for_each - iterate through all stored pointers

   * @idr: idr handle

   * @fn: function to be called for each pointer

   * @data: data passed to callback function

   *

   * The callback function will be called for each entry in @idr, passing
   * the id, the pointer and the data pointer passed to this function.

   *

   * If @fn returns anything other than %0, the iteration stops and that
   * value is returned from this function.

   *

   * idr_for_each() can be called concurrently with idr_alloc() and
   * idr_remove() if protected by RCU.  Newly added entries may not be
   * seen and deleted entries may be seen, but adding and removing entries
   * will not cause other entries to be skipped, nor spurious ones to be seen.

   */

  int idr_for_each(const struct idr *idr,
  		int (*fn)(int id, void *p, void *data), void *data)

  {

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
  		int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
  		if (ret)
  			return ret;

  	}

  	return 0;

  }
  EXPORT_SYMBOL(idr_for_each);
  
  /**

   * idr_get_next - Find next populated entry
   * @idr: idr handle
   * @nextid: Pointer to lowest possible ID to return
   *
   * Returns the next populated entry in the tree with an ID greater than
   * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
   * to the ID of the found value.  To use in a loop, the value pointed to by
   * nextid must be incremented by the user.

   */

  void *idr_get_next(struct idr *idr, int *nextid)

  {

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
  	if (!slot)

  		return NULL;

  	*nextid = iter.index;
  	return rcu_dereference_raw(*slot);

  }

  EXPORT_SYMBOL(idr_get_next);

  void *idr_get_next_ext(struct idr *idr, unsigned long *nextid)
  {
  	struct radix_tree_iter iter;
  	void __rcu **slot;
  
  	slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
  	if (!slot)
  		return NULL;
  
  	*nextid = iter.index;
  	return rcu_dereference_raw(*slot);
  }
  EXPORT_SYMBOL(idr_get_next_ext);

  /**

   * idr_replace - replace pointer for given id

   * @idr: idr handle
   * @ptr: New pointer to associate with the ID
   * @id: Lookup key

   *

   * Replace the pointer registered with an ID and return the old value.
   * This function can be called under the RCU read lock concurrently with
   * idr_alloc() and idr_remove() (as long as the ID being removed is not
   * the one being replaced!).

   *

   * Returns: the old value on success.  %-ENOENT indicates that @id was not
   * found.  %-EINVAL indicates that @id or @ptr were not valid.

   */

  void *idr_replace(struct idr *idr, void *ptr, int id)

  {

  	if (id < 0)

  		return ERR_PTR(-EINVAL);
  
  	return idr_replace_ext(idr, ptr, id);
  }
  EXPORT_SYMBOL(idr_replace);
  
  void *idr_replace_ext(struct idr *idr, void *ptr, unsigned long id)
  {

  	struct radix_tree_node *node;

  	void __rcu **slot = NULL;

  	void *entry;

  	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))

  		return ERR_PTR(-EINVAL);

  	entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
  	if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))

  		return ERR_PTR(-ENOENT);

  	__radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);

  	return entry;

  }

  EXPORT_SYMBOL(idr_replace_ext);

  /**
   * DOC: IDA description

   *

   * The IDA is an ID allocator which does not provide the ability to
   * associate an ID with a pointer.  As such, it only needs to store one
   * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
   * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
   * then initialise it using ida_init()).  To allocate a new ID, call
   * ida_simple_get().  To free an ID, call ida_simple_remove().
   *
   * If you have more complex locking requirements, use a loop around
   * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
   * ida_remove() to free an ID.  You must make sure that ida_get_new() and
   * ida_remove() cannot be called at the same time as each other for the
   * same IDA.
   *
   * You can also use ida_get_new_above() if you need an ID to be allocated
   * above a particular number.  ida_destroy() can be used to dispose of an
   * IDA without needing to free the individual IDs in it.  You can use
   * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
   *
   * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
   * limitation, it should be quite straightforward to raise the maximum.

   */

  /*
   * Developer's notes:
   *
   * The IDA uses the functionality provided by the IDR & radix tree to store
   * bitmaps in each entry.  The IDR_FREE tag means there is at least one bit
   * free, unlike the IDR where it means at least one entry is free.
   *
   * I considered telling the radix tree that each slot is an order-10 node
   * and storing the bit numbers in the radix tree, but the radix tree can't
   * allow a single multiorder entry at index 0, which would significantly
   * increase memory consumption for the IDA.  So instead we divide the index
   * by the number of bits in the leaf bitmap before doing a radix tree lookup.
   *
   * As an optimisation, if there are only a few low bits set in any given
   * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
   * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
   * directly in the entry.  By being really tricksy, we could store
   * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
   * for 0-3 allocated IDs.
   *
   * We allow the radix tree 'exceptional' count to get out of date.  Nothing
   * in the IDA nor the radix tree code checks it.  If it becomes important
   * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
   * calls to radix_tree_iter_replace() which will correct the exceptional
   * count.
   *
   * The IDA always requires a lock to alloc/free.  If we add a 'test_bit'
   * equivalent, it will still need locking.  Going to RCU lookup would require
   * using RCU to free bitmaps, and that's not trivial without embedding an
   * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
   * bitmap, which is excessive.
   */

  #define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)

  /**
   * ida_get_new_above - allocate new ID above or equal to a start id

   * @ida: ida handle
   * @start: id to start search at
   * @id: pointer to the allocated handle

   *

   * Allocate new ID above or equal to @start.  It should be called
   * with any required locks to ensure that concurrent calls to
   * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
   * Consider using ida_simple_get() if you do not have complex locking
   * requirements.

   *

   * 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.  On success, it will return 0.

   *

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

   */

  int ida_get_new_above(struct ida *ida, int start, int *id)

  {

  	struct radix_tree_root *root = &ida->ida_rt;

  	void __rcu **slot;

  	struct radix_tree_iter iter;

  	struct ida_bitmap *bitmap;

  	unsigned long index;

  	unsigned bit, ebit;

  	int new;
  
  	index = start / IDA_BITMAP_BITS;
  	bit = start % IDA_BITMAP_BITS;

  	ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;

  
  	slot = radix_tree_iter_init(&iter, index);
  	for (;;) {
  		if (slot)
  			slot = radix_tree_next_slot(slot, &iter,
  						RADIX_TREE_ITER_TAGGED);
  		if (!slot) {
  			slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
  			if (IS_ERR(slot)) {
  				if (slot == ERR_PTR(-ENOMEM))
  					return -EAGAIN;
  				return PTR_ERR(slot);
  			}
  		}

  		if (iter.index > index) {

  			bit = 0;

  			ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
  		}

  		new = iter.index * IDA_BITMAP_BITS;
  		bitmap = rcu_dereference_raw(*slot);

  		if (radix_tree_exception(bitmap)) {
  			unsigned long tmp = (unsigned long)bitmap;
  			ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
  			if (ebit < BITS_PER_LONG) {
  				tmp |= 1UL << ebit;
  				rcu_assign_pointer(*slot, (void *)tmp);
  				*id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
  				return 0;
  			}
  			bitmap = this_cpu_xchg(ida_bitmap, NULL);
  			if (!bitmap)
  				return -EAGAIN;
  			memset(bitmap, 0, sizeof(*bitmap));
  			bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
  			rcu_assign_pointer(*slot, bitmap);
  		}

  		if (bitmap) {
  			bit = find_next_zero_bit(bitmap->bitmap,
  							IDA_BITMAP_BITS, bit);
  			new += bit;
  			if (new < 0)
  				return -ENOSPC;
  			if (bit == IDA_BITMAP_BITS)
  				continue;

  			__set_bit(bit, bitmap->bitmap);
  			if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
  				radix_tree_iter_tag_clear(root, &iter,
  								IDR_FREE);
  		} else {
  			new += bit;
  			if (new < 0)
  				return -ENOSPC;

  			if (ebit < BITS_PER_LONG) {
  				bitmap = (void *)((1UL << ebit) |
  						RADIX_TREE_EXCEPTIONAL_ENTRY);
  				radix_tree_iter_replace(root, &iter, slot,
  						bitmap);
  				*id = new;
  				return 0;
  			}

  			bitmap = this_cpu_xchg(ida_bitmap, NULL);

  			if (!bitmap)
  				return -EAGAIN;

  			memset(bitmap, 0, sizeof(*bitmap));
  			__set_bit(bit, bitmap->bitmap);
  			radix_tree_iter_replace(root, &iter, slot, bitmap);
  		}

  		*id = new;
  		return 0;

  	}

  }
  EXPORT_SYMBOL(ida_get_new_above);
  
  /**

   * ida_remove - Free the given ID
   * @ida: ida handle
   * @id: ID to free
   *
   * This function should not be called at the same time as ida_get_new_above().

   */
  void ida_remove(struct ida *ida, int id)
  {

  	unsigned long index = id / IDA_BITMAP_BITS;
  	unsigned offset = id % IDA_BITMAP_BITS;

  	struct ida_bitmap *bitmap;

  	unsigned long *btmp;

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
  	if (!slot)

  		goto err;

  	bitmap = rcu_dereference_raw(*slot);

  	if (radix_tree_exception(bitmap)) {
  		btmp = (unsigned long *)slot;
  		offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
  		if (offset >= BITS_PER_LONG)
  			goto err;
  	} else {
  		btmp = bitmap->bitmap;
  	}
  	if (!test_bit(offset, btmp))

  		goto err;

  	__clear_bit(offset, btmp);

  	radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);

  	if (radix_tree_exception(bitmap)) {
  		if (rcu_dereference_raw(*slot) ==
  					(void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
  			radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
  	} else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {

  		kfree(bitmap);
  		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);

  	}

  	return;

   err:

  	WARN(1, "ida_remove called for id=%d which is not allocated.
  ", id);

  }
  EXPORT_SYMBOL(ida_remove);
  
  /**

   * ida_destroy - Free the contents of an ida
   * @ida: ida handle
   *
   * Calling this function releases all resources associated with an IDA.  When
   * this call returns, the IDA is empty and can be reused or freed.  The caller
   * should not allow ida_remove() or ida_get_new_above() to be called at the
   * same time.

   */
  void ida_destroy(struct ida *ida)
  {

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  
  	radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
  		struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);

  		if (!radix_tree_exception(bitmap))
  			kfree(bitmap);

  		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
  	}

  }
  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.
   *

   * Compared to ida_get_new_above() this function does its own locking, and
   * should be used unless there are special requirements.
   *

   * 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.

   *
   * Use to release an id allocated with ida_simple_get().
   *
   * Compared to ida_remove() this function does its own locking, and should be
   * used unless there are special requirements.

   */
  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);