radix-tree: add radix_tree_prev_hole()

			unsigned long first_index, unsigned int max_items);

unsigned long radix_tree_next_hole(struct radix_tree_root *root,

				unsigned long index, unsigned long max_scan);

unsigned long radix_tree_prev_hole(struct radix_tree_root *root,

				unsigned long index, unsigned long max_scan);

int radix_tree_preload(gfp_t gfp_mask);

void radix_tree_init(void);

void *radix_tree_tag_set(struct radix_tree_root *root,

}

EXPORT_SYMBOL(radix_tree_next_hole);

/**

 *	radix_tree_prev_hole    -    find the prev hole (not-present entry)

 *	@root:		tree root

 *	@index:		index key

 *	@max_scan:	maximum range to search

 *

 *	Search backwards in the range [max(index-max_scan+1, 0), index]

 *	for the first hole.

 *

 *	Returns: the index of the hole if found, otherwise returns an index

 *	outside of the set specified (in which case 'index - return >= max_scan'

 *	will be true). In rare cases of wrap-around, LONG_MAX will be returned.

 *

 *	radix_tree_next_hole may be called under rcu_read_lock. However, like

 *	radix_tree_gang_lookup, this will not atomically search a snapshot of

 *	the tree at a single point in time. For example, if a hole is created

 *	at index 10, then subsequently a hole is created at index 5,

 *	radix_tree_prev_hole covering both indexes may return 5 if called under

 *	rcu_read_lock.

 */

unsigned long radix_tree_prev_hole(struct radix_tree_root *root,

				   unsigned long index, unsigned long max_scan)

{

	unsigned long i;

	for (i = 0; i < max_scan; i++) {

		if (!radix_tree_lookup(root, index))

			break;

		index--;

		if (index == LONG_MAX)

			break;

	}

	return index;

}

EXPORT_SYMBOL(radix_tree_prev_hole);

static unsigned int

__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,

	unsigned int max_items, unsigned long *next_index)