#include <linux/bitmap.h>

  #include <linux/bug.h>

  #include <linux/export.h>

  #include <linux/idr.h>

  #include <linux/slab.h>

  #include <linux/spinlock.h>

  #include <linux/xarray.h>

  DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);

  /**
   * idr_alloc_u32() - Allocate an ID.
   * @idr: IDR handle.
   * @ptr: Pointer to be associated with the new ID.
   * @nextid: Pointer to an ID.
   * @max: The maximum ID to allocate (inclusive).
   * @gfp: Memory allocation flags.
   *
   * Allocates an unused ID in the range specified by @nextid and @max.
   * Note that @max is inclusive whereas the @end parameter to idr_alloc()

   * is exclusive.  The new ID is assigned to @nextid before the pointer
   * is inserted into the IDR, so if @nextid points into the object pointed
   * to by @ptr, a concurrent lookup will not find an uninitialised ID.

   *
   * The caller should provide their own locking to ensure that two
   * concurrent modifications to the IDR are not possible.  Read-only
   * accesses to the IDR may be done under the RCU read lock or may
   * exclude simultaneous writers.
   *
   * Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
   * or -ENOSPC if no free IDs could be found.  If an error occurred,
   * @nextid is unchanged.
   */
  int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
  			unsigned long max, gfp_t gfp)
  {

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	unsigned int base = idr->idr_base;
  	unsigned int id = *nextid;

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

  	if (WARN_ON_ONCE(!(idr->idr_rt.gfp_mask & ROOT_IS_IDR)))
  		idr->idr_rt.gfp_mask |= IDR_RT_MARKER;

  	id = (id < base) ? 0 : id - base;
  	radix_tree_iter_init(&iter, id);
  	slot = idr_get_free(&idr->idr_rt, &iter, gfp, max - base);

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

  	*nextid = iter.index + base;

  	/* there is a memory barrier inside radix_tree_iter_replace() */

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

  	return 0;

  }

  EXPORT_SYMBOL_GPL(idr_alloc_u32);

  /**

   * idr_alloc() - Allocate an ID.
   * @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 unused ID in the range specified by @start and @end.  If
   * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
   * callers to use @start + N as @end as long as N is within integer range.
   *
   * The caller should provide their own locking to ensure that two
   * concurrent modifications to the IDR are not possible.  Read-only
   * accesses to the IDR may be done under the RCU read lock or may
   * exclude simultaneous writers.
   *
   * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
   * or -ENOSPC if no free IDs could be found.

   */

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

  {

  	u32 id = start;
  	int ret;
  
  	if (WARN_ON_ONCE(start < 0))
  		return -EINVAL;
  
  	ret = idr_alloc_u32(idr, ptr, &id, end > 0 ? end - 1 : INT_MAX, gfp);
  	if (ret)
  		return ret;

  	return id;
  }
  EXPORT_SYMBOL_GPL(idr_alloc);
  
  /**
   * idr_alloc_cyclic() - Allocate an ID cyclically.
   * @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 unused ID in the range specified by @nextid and @end.  If
   * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
   * callers to use @start + N as @end as long as N is within integer range.
   * The search for an unused ID will start at the last ID allocated and will
   * wrap around to @start if no free IDs are found before reaching @end.
   *
   * The caller should provide their own locking to ensure that two
   * concurrent modifications to the IDR are not possible.  Read-only
   * accesses to the IDR may be done under the RCU read lock or may
   * exclude simultaneous writers.
   *
   * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
   * or -ENOSPC if no free IDs could be found.
   */
  int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
  {
  	u32 id = idr->idr_next;
  	int err, max = end > 0 ? end - 1 : INT_MAX;

  	if ((int)id < start)
  		id = start;

  	err = idr_alloc_u32(idr, ptr, &id, max, gfp);
  	if ((err == -ENOSPC) && (id > start)) {
  		id = start;
  		err = idr_alloc_u32(idr, ptr, &id, max, gfp);
  	}
  	if (err)
  		return err;

  	idr->idr_next = id + 1;

  	return id;

  }

  EXPORT_SYMBOL(idr_alloc_cyclic);

  /**

   * idr_remove() - Remove an ID from the IDR.
   * @idr: IDR handle.
   * @id: Pointer ID.
   *
   * Removes this ID from the IDR.  If the ID was not previously in the IDR,
   * this function returns %NULL.
   *
   * Since this function modifies the IDR, the caller should provide their
   * own locking to ensure that concurrent modification of the same IDR is
   * not possible.
   *
   * Return: The pointer formerly associated with this ID.
   */
  void *idr_remove(struct idr *idr, unsigned long id)
  {
  	return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
  }
  EXPORT_SYMBOL_GPL(idr_remove);
  
  /**
   * idr_find() - Return pointer for given ID.
   * @idr: IDR handle.
   * @id: Pointer ID.
   *
   * Looks up the pointer associated with this ID.  A %NULL pointer may
   * indicate that @id is not allocated or that the %NULL pointer was
   * associated with this ID.
   *
   * This function can be called under rcu_read_lock(), given that the leaf
   * pointers lifetimes are correctly managed.
   *
   * Return: The pointer associated with this ID.
   */
  void *idr_find(const struct idr *idr, unsigned long id)
  {
  	return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
  }
  EXPORT_SYMBOL_GPL(idr_find);
  
  /**

   * 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 entry and @data.

   *

   * 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;

  	int base = idr->idr_base;

  	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {

  		int ret;

  		unsigned long id = iter.index + base;

  		if (WARN_ON_ONCE(id > INT_MAX))

  			break;

  		ret = fn(id, 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 an ID.

   *
   * 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;

  	unsigned long base = idr->idr_base;
  	unsigned long id = *nextid;

  	id = (id < base) ? 0 : id - base;
  	slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);

  	if (!slot)

  		return NULL;

  	id = iter.index + base;

  	if (WARN_ON_ONCE(id > INT_MAX))

  		return NULL;

  	*nextid = id;

  	return rcu_dereference_raw(*slot);

  }

  EXPORT_SYMBOL(idr_get_next);

  /**
   * idr_get_next_ul() - Find next populated entry.
   * @idr: IDR handle.
   * @nextid: Pointer to an ID.
   *
   * 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_ul(struct idr *idr, unsigned long *nextid)

  {
  	struct radix_tree_iter iter;
  	void __rcu **slot;

  	unsigned long base = idr->idr_base;
  	unsigned long id = *nextid;

  	id = (id < base) ? 0 : id - base;
  	slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);

  	if (!slot)
  		return NULL;

  	*nextid = iter.index + base;

  	return rcu_dereference_raw(*slot);
  }

  EXPORT_SYMBOL(idr_get_next_ul);

  /**

   * idr_replace() - replace pointer for given ID.
   * @idr: IDR handle.
   * @ptr: New pointer to associate with the ID.
   * @id: ID to change.

   *

   * 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 @ptr was not valid.

   */

  void *idr_replace(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);

  	id -= idr->idr_base;

  	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);

  	return entry;

  }

  EXPORT_SYMBOL(idr_replace);

  /**
   * 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_alloc(), ida_alloc_min(), ida_alloc_max() or ida_alloc_range().
   * To free an ID, call ida_free().

   *

   * 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 - 1)

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

  {

  	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);

  				return new + ebit -
  					RADIX_TREE_EXCEPTIONAL_SHIFT;

  			}
  			bitmap = this_cpu_xchg(ida_bitmap, NULL);
  			if (!bitmap)
  				return -EAGAIN;

  			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);

  				return new;

  			}

  			bitmap = this_cpu_xchg(ida_bitmap, NULL);

  			if (!bitmap)
  				return -EAGAIN;

  			__set_bit(bit, bitmap->bitmap);
  			radix_tree_iter_replace(root, &iter, slot, bitmap);
  		}

  		return new;

  	}

  }

  static 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_free called for id=%d which is not allocated.
  ", id);

  }

  
  /**

   * ida_destroy() - Free all IDs.
   * @ida: IDA handle.
   *
   * Calling this function frees all IDs and releases all resources used
   * by an IDA.  When this call returns, the IDA is empty and can be reused
   * or freed.  If the IDA is already empty, there is no need to call this
   * function.

   *

   * Context: Any context.

   */
  void ida_destroy(struct ida *ida)
  {

  	unsigned long flags;

  	struct radix_tree_iter iter;

  	void __rcu **slot;

  	xa_lock_irqsave(&ida->ida_rt, flags);

  	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);
  	}

  	xa_unlock_irqrestore(&ida->ida_rt, flags);

  }
  EXPORT_SYMBOL(ida_destroy);
  
  /**

   * ida_alloc_range() - Allocate an unused ID.
   * @ida: IDA handle.
   * @min: Lowest ID to allocate.
   * @max: Highest ID to allocate.
   * @gfp: Memory allocation flags.

   *

   * Allocate an ID between @min and @max, inclusive.  The allocated ID will
   * not exceed %INT_MAX, even if @max is larger.

   *

   * Context: Any context.
   * Return: The allocated ID, or %-ENOMEM if memory could not be allocated,
   * or %-ENOSPC if there are no free IDs.

   */

  int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
  			gfp_t gfp)

  {

  	int id = 0;

  	unsigned long flags;

  	if ((int)min < 0)
  		return -ENOSPC;

  	if ((int)max < 0)
  		max = INT_MAX;

  
  again:

  	xa_lock_irqsave(&ida->ida_rt, flags);

  	id = ida_get_new_above(ida, min);
  	if (id > (int)max) {
  		ida_remove(ida, id);
  		id = -ENOSPC;

  	}

  	xa_unlock_irqrestore(&ida->ida_rt, flags);

  	if (unlikely(id == -EAGAIN)) {

  		if (!ida_pre_get(ida, gfp))
  			return -ENOMEM;

  		goto again;

  	}

  	return id;

  }

  EXPORT_SYMBOL(ida_alloc_range);

  
  /**

   * ida_free() - Release an allocated ID.
   * @ida: IDA handle.
   * @id: Previously allocated ID.

   *

   * Context: Any context.

   */

  void ida_free(struct ida *ida, unsigned int id)

  {

  	unsigned long flags;

  	BUG_ON((int)id < 0);

  	xa_lock_irqsave(&ida->ida_rt, flags);

  	ida_remove(ida, id);

  	xa_unlock_irqrestore(&ida->ida_rt, flags);

  }

  EXPORT_SYMBOL(ida_free);