text: // SPDX-License-Identifier: GPL-2.0-only
  #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>
  
  /**
   * 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(!(idr->idr_rt.xa_flags & ROOT_IS_IDR)))
  		idr->idr_rt.xa_flags |= 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;
  	void *entry = NULL;
  	unsigned long base = idr->idr_base;
  	unsigned long id = *nextid;
  
  	id = (id < base) ? 0 : id - base;
  	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, id) {
  		entry = rcu_dereference_raw(*slot);
  		if (!entry)
  			continue;
  		if (!xa_is_internal(entry))
  			break;
  		if (slot != &idr->idr_rt.xa_head && !xa_is_retry(entry))
  			break;
  		slot = radix_tree_iter_retry(&iter);
  	}
  	if (!slot)
  		return NULL;
  	id = iter.index + base;
  
  	if (WARN_ON_ONCE(id > INT_MAX))
  		return NULL;
  
  	*nextid = id;
  	return entry;
  }
  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;
  
  	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);
  
  	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.
   *
   * The IDA handles its own locking.  It is safe to call any of the IDA
   * functions without synchronisation in your code.
   *
   * 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 XArray to store bitmaps in
   * each entry.  The XA_FREE_MARK is only cleared when all bits in the bitmap
   * have been set.
   *
   * I considered telling the XArray that each slot is an order-10 node
   * and indexing by bit number, but the XArray can't allow a single multi-index
   * entry in the head, 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 store the bits
   * as a value entry.  Value entries never have the XA_FREE_MARK cleared
   * because we can always convert them into a bitmap entry.
   *
   * It would be possible to optimise further; once we've run out of a
   * single 128-byte bitmap, we currently switch to a 576-byte node, put
   * the 128-byte bitmap in the first entry and then start allocating extra
   * 128-byte entries.  We could instead use the 512 bytes of the node's
   * data as a bitmap before moving to that scheme.  I do not believe this
   * is a worthwhile optimisation; Rasmus Villemoes surveyed the current
   * users of the IDA and almost none of them use more than 1024 entries.
   * Those that do use more than the 8192 IDs that the 512 bytes would
   * provide.
   *
   * The IDA always uses 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.
   */
  
  /**
   * 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)
  {
  	XA_STATE(xas, &ida->xa, min / IDA_BITMAP_BITS);
  	unsigned bit = min % IDA_BITMAP_BITS;
  	unsigned long flags;
  	struct ida_bitmap *bitmap, *alloc = NULL;
  
  	if ((int)min < 0)
  		return -ENOSPC;
  
  	if ((int)max < 0)
  		max = INT_MAX;
  
  retry:
  	xas_lock_irqsave(&xas, flags);
  next:
  	bitmap = xas_find_marked(&xas, max / IDA_BITMAP_BITS, XA_FREE_MARK);
  	if (xas.xa_index > min / IDA_BITMAP_BITS)
  		bit = 0;
  	if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
  		goto nospc;
  
  	if (xa_is_value(bitmap)) {
  		unsigned long tmp = xa_to_value(bitmap);
  
  		if (bit < BITS_PER_XA_VALUE) {
  			bit = find_next_zero_bit(&tmp, BITS_PER_XA_VALUE, bit);
  			if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
  				goto nospc;
  			if (bit < BITS_PER_XA_VALUE) {
  				tmp |= 1UL << bit;
  				xas_store(&xas, xa_mk_value(tmp));
  				goto out;
  			}
  		}
  		bitmap = alloc;
  		if (!bitmap)
  			bitmap = kzalloc(sizeof(*bitmap), GFP_NOWAIT);
  		if (!bitmap)
  			goto alloc;
  		bitmap->bitmap[0] = tmp;
  		xas_store(&xas, bitmap);
  		if (xas_error(&xas)) {
  			bitmap->bitmap[0] = 0;
  			goto out;
  		}
  	}
  
  	if (bitmap) {
  		bit = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, bit);
  		if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
  			goto nospc;
  		if (bit == IDA_BITMAP_BITS)
  			goto next;
  
  		__set_bit(bit, bitmap->bitmap);
  		if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
  			xas_clear_mark(&xas, XA_FREE_MARK);
  	} else {
  		if (bit < BITS_PER_XA_VALUE) {
  			bitmap = xa_mk_value(1UL << bit);
  		} else {
  			bitmap = alloc;
  			if (!bitmap)
  				bitmap = kzalloc(sizeof(*bitmap), GFP_NOWAIT);
  			if (!bitmap)
  				goto alloc;
  			__set_bit(bit, bitmap->bitmap);
  		}
  		xas_store(&xas, bitmap);
  	}
  out:
  	xas_unlock_irqrestore(&xas, flags);
  	if (xas_nomem(&xas, gfp)) {
  		xas.xa_index = min / IDA_BITMAP_BITS;
  		bit = min % IDA_BITMAP_BITS;
  		goto retry;
  	}
  	if (bitmap != alloc)
  		kfree(alloc);
  	if (xas_error(&xas))
  		return xas_error(&xas);
  	return xas.xa_index * IDA_BITMAP_BITS + bit;
  alloc:
  	xas_unlock_irqrestore(&xas, flags);
  	alloc = kzalloc(sizeof(*bitmap), gfp);
  	if (!alloc)
  		return -ENOMEM;
  	xas_set(&xas, min / IDA_BITMAP_BITS);
  	bit = min % IDA_BITMAP_BITS;
  	goto retry;
  nospc:
  	xas_unlock_irqrestore(&xas, flags);
  	return -ENOSPC;
  }
  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)
  {
  	XA_STATE(xas, &ida->xa, id / IDA_BITMAP_BITS);
  	unsigned bit = id % IDA_BITMAP_BITS;
  	struct ida_bitmap *bitmap;
  	unsigned long flags;
  
  	BUG_ON((int)id < 0);
  
  	xas_lock_irqsave(&xas, flags);
  	bitmap = xas_load(&xas);
  
  	if (xa_is_value(bitmap)) {
  		unsigned long v = xa_to_value(bitmap);
  		if (bit >= BITS_PER_XA_VALUE)
  			goto err;
  		if (!(v & (1UL << bit)))
  			goto err;
  		v &= ~(1UL << bit);
  		if (!v)
  			goto delete;
  		xas_store(&xas, xa_mk_value(v));
  	} else {
  		if (!test_bit(bit, bitmap->bitmap))
  			goto err;
  		__clear_bit(bit, bitmap->bitmap);
  		xas_set_mark(&xas, XA_FREE_MARK);
  		if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
  			kfree(bitmap);
  delete:
  			xas_store(&xas, NULL);
  		}
  	}
  	xas_unlock_irqrestore(&xas, flags);
  	return;
   err:
  	xas_unlock_irqrestore(&xas, flags);
  	WARN(1, "ida_free called for id=%d which is not allocated.\n", id);
  }
  EXPORT_SYMBOL(ida_free);
  
  /**
   * 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)
  {
  	XA_STATE(xas, &ida->xa, 0);
  	struct ida_bitmap *bitmap;
  	unsigned long flags;
  
  	xas_lock_irqsave(&xas, flags);
  	xas_for_each(&xas, bitmap, ULONG_MAX) {
  		if (!xa_is_value(bitmap))
  			kfree(bitmap);
  		xas_store(&xas, NULL);
  	}
  	xas_unlock_irqrestore(&xas, flags);
  }
  EXPORT_SYMBOL(ida_destroy);
  
  #ifndef __KERNEL__
  extern void xa_dump_index(unsigned long index, unsigned int shift);
  #define IDA_CHUNK_SHIFT		ilog2(IDA_BITMAP_BITS)
  
  static void ida_dump_entry(void *entry, unsigned long index)
  {
  	unsigned long i;
  
  	if (!entry)
  		return;
  
  	if (xa_is_node(entry)) {
  		struct xa_node *node = xa_to_node(entry);
  		unsigned int shift = node->shift + IDA_CHUNK_SHIFT +
  			XA_CHUNK_SHIFT;
  
  		xa_dump_index(index * IDA_BITMAP_BITS, shift);
  		xa_dump_node(node);
  		for (i = 0; i < XA_CHUNK_SIZE; i++)
  			ida_dump_entry(node->slots[i],
  					index | (i << node->shift));
  	} else if (xa_is_value(entry)) {
  		xa_dump_index(index * IDA_BITMAP_BITS, ilog2(BITS_PER_LONG));
  		pr_cont("value: data %lx [%px]\n", xa_to_value(entry), entry);
  	} else {
  		struct ida_bitmap *bitmap = entry;
  
  		xa_dump_index(index * IDA_BITMAP_BITS, IDA_CHUNK_SHIFT);
  		pr_cont("bitmap: %p data", bitmap);
  		for (i = 0; i < IDA_BITMAP_LONGS; i++)
  			pr_cont(" %lx", bitmap->bitmap[i]);
  		pr_cont("\n");
  	}
  }
  
  static void ida_dump(struct ida *ida)
  {
  	struct xarray *xa = &ida->xa;
  	pr_debug("ida: %p node %p free %d\n", ida, xa->xa_head,
  				xa->xa_flags >> ROOT_TAG_SHIFT);
  	ida_dump_entry(xa->xa_head, 0);
  }
  #endif
  