#include <linux/export.h>
  #include <linux/generic-radix-tree.h>
  #include <linux/gfp.h>

  #include <linux/kmemleak.h>

  
  #define GENRADIX_ARY		(PAGE_SIZE / sizeof(struct genradix_node *))
  #define GENRADIX_ARY_SHIFT	ilog2(GENRADIX_ARY)
  
  struct genradix_node {
  	union {
  		/* Interior node: */
  		struct genradix_node	*children[GENRADIX_ARY];
  
  		/* Leaf: */
  		u8			data[PAGE_SIZE];
  	};
  };
  
  static inline int genradix_depth_shift(unsigned depth)
  {
  	return PAGE_SHIFT + GENRADIX_ARY_SHIFT * depth;
  }
  
  /*
   * Returns size (of data, in bytes) that a tree of a given depth holds:
   */
  static inline size_t genradix_depth_size(unsigned depth)
  {
  	return 1UL << genradix_depth_shift(depth);
  }
  
  /* depth that's needed for a genradix that can address up to ULONG_MAX: */
  #define GENRADIX_MAX_DEPTH	\
  	DIV_ROUND_UP(BITS_PER_LONG - PAGE_SHIFT, GENRADIX_ARY_SHIFT)
  
  #define GENRADIX_DEPTH_MASK				\
  	((unsigned long) (roundup_pow_of_two(GENRADIX_MAX_DEPTH + 1) - 1))

  static inline unsigned genradix_root_to_depth(struct genradix_root *r)

  {
  	return (unsigned long) r & GENRADIX_DEPTH_MASK;
  }

  static inline struct genradix_node *genradix_root_to_node(struct genradix_root *r)

  {
  	return (void *) ((unsigned long) r & ~GENRADIX_DEPTH_MASK);
  }
  
  /*
   * Returns pointer to the specified byte @offset within @radix, or NULL if not
   * allocated
   */
  void *__genradix_ptr(struct __genradix *radix, size_t offset)
  {
  	struct genradix_root *r = READ_ONCE(radix->root);
  	struct genradix_node *n = genradix_root_to_node(r);
  	unsigned level		= genradix_root_to_depth(r);
  
  	if (ilog2(offset) >= genradix_depth_shift(level))
  		return NULL;
  
  	while (1) {
  		if (!n)
  			return NULL;
  		if (!level)
  			break;
  
  		level--;
  
  		n = n->children[offset >> genradix_depth_shift(level)];
  		offset &= genradix_depth_size(level) - 1;
  	}
  
  	return &n->data[offset];
  }
  EXPORT_SYMBOL(__genradix_ptr);

  static inline struct genradix_node *genradix_alloc_node(gfp_t gfp_mask)
  {
  	struct genradix_node *node;
  
  	node = (struct genradix_node *)__get_free_page(gfp_mask|__GFP_ZERO);
  
  	/*
  	 * We're using pages (not slab allocations) directly for kernel data
  	 * structures, so we need to explicitly inform kmemleak of them in order
  	 * to avoid false positive memory leak reports.
  	 */
  	kmemleak_alloc(node, PAGE_SIZE, 1, gfp_mask);
  	return node;
  }
  
  static inline void genradix_free_node(struct genradix_node *node)
  {
  	kmemleak_free(node);
  	free_page((unsigned long)node);
  }

  /*
   * Returns pointer to the specified byte @offset within @radix, allocating it if
   * necessary - newly allocated slots are always zeroed out:
   */
  void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset,
  			   gfp_t gfp_mask)
  {
  	struct genradix_root *v = READ_ONCE(radix->root);
  	struct genradix_node *n, *new_node = NULL;
  	unsigned level;
  
  	/* Increase tree depth if necessary: */
  	while (1) {
  		struct genradix_root *r = v, *new_root;
  
  		n	= genradix_root_to_node(r);
  		level	= genradix_root_to_depth(r);
  
  		if (n && ilog2(offset) < genradix_depth_shift(level))
  			break;
  
  		if (!new_node) {

  			new_node = genradix_alloc_node(gfp_mask);

  			if (!new_node)
  				return NULL;
  		}
  
  		new_node->children[0] = n;
  		new_root = ((struct genradix_root *)
  			    ((unsigned long) new_node | (n ? level + 1 : 0)));
  
  		if ((v = cmpxchg_release(&radix->root, r, new_root)) == r) {
  			v = new_root;
  			new_node = NULL;
  		}
  	}
  
  	while (level--) {
  		struct genradix_node **p =
  			&n->children[offset >> genradix_depth_shift(level)];
  		offset &= genradix_depth_size(level) - 1;
  
  		n = READ_ONCE(*p);
  		if (!n) {
  			if (!new_node) {

  				new_node = genradix_alloc_node(gfp_mask);

  				if (!new_node)
  					return NULL;
  			}
  
  			if (!(n = cmpxchg_release(p, NULL, new_node)))
  				swap(n, new_node);
  		}
  	}
  
  	if (new_node)

  		genradix_free_node(new_node);

  
  	return &n->data[offset];
  }
  EXPORT_SYMBOL(__genradix_ptr_alloc);
  
  void *__genradix_iter_peek(struct genradix_iter *iter,
  			   struct __genradix *radix,
  			   size_t objs_per_page)
  {
  	struct genradix_root *r;
  	struct genradix_node *n;
  	unsigned level, i;
  restart:
  	r = READ_ONCE(radix->root);
  	if (!r)
  		return NULL;
  
  	n	= genradix_root_to_node(r);
  	level	= genradix_root_to_depth(r);
  
  	if (ilog2(iter->offset) >= genradix_depth_shift(level))
  		return NULL;
  
  	while (level) {
  		level--;
  
  		i = (iter->offset >> genradix_depth_shift(level)) &
  			(GENRADIX_ARY - 1);
  
  		while (!n->children[i]) {
  			i++;
  			iter->offset = round_down(iter->offset +
  					   genradix_depth_size(level),
  					   genradix_depth_size(level));
  			iter->pos = (iter->offset >> PAGE_SHIFT) *
  				objs_per_page;
  			if (i == GENRADIX_ARY)
  				goto restart;
  		}
  
  		n = n->children[i];
  	}
  
  	return &n->data[iter->offset & (PAGE_SIZE - 1)];
  }
  EXPORT_SYMBOL(__genradix_iter_peek);
  
  static void genradix_free_recurse(struct genradix_node *n, unsigned level)
  {
  	if (level) {
  		unsigned i;
  
  		for (i = 0; i < GENRADIX_ARY; i++)
  			if (n->children[i])
  				genradix_free_recurse(n->children[i], level - 1);
  	}

  	genradix_free_node(n);

  }
  
  int __genradix_prealloc(struct __genradix *radix, size_t size,
  			gfp_t gfp_mask)
  {
  	size_t offset;
  
  	for (offset = 0; offset < size; offset += PAGE_SIZE)
  		if (!__genradix_ptr_alloc(radix, offset, gfp_mask))
  			return -ENOMEM;
  
  	return 0;
  }
  EXPORT_SYMBOL(__genradix_prealloc);
  
  void __genradix_free(struct __genradix *radix)
  {
  	struct genradix_root *r = xchg(&radix->root, NULL);
  
  	genradix_free_recurse(genradix_root_to_node(r),
  			      genradix_root_to_depth(r));
  }
  EXPORT_SYMBOL(__genradix_free);