2 files changed, 38 insertions, 0 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index f9e77d2ee320..430e4a8c1382 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -155,6 +155,8 @@ void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 unsigned int
 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
                         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);
 int radix_tree_preload(gfp_t gfp_mask);
 void radix_tree_init(void);
 void *radix_tree_tag_set(struct radix_tree_root *root,
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 514efb200be6..7af368a4401b 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -599,6 +599,42 @@ int radix_tree_tag_get(struct radix_tree_root *root,
 EXPORT_SYMBOL(radix_tree_tag_get);
 #endif
 
+/**
+ *      radix_tree_next_hole    -    find the next hole (not-present entry)
+ *      @root:          tree root
+ *      @index:         index key
+ *      @max_scan:      maximum range to search
+ *
+ *      Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the lowest
+ *      indexed hole.
+ *
+ *      Returns: the index of the hole if found, otherwise returns an index
+ *      outside of the set specified (in which case 'return - index >= max_scan'
+ *      will be true).
+ *
+ *      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
+ *      5, then subsequently a hole is created at index 10, radix_tree_next_hole
+ *      covering both indexes may return 10 if called under rcu_read_lock.
+ */
+unsigned long radix_tree_next_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 == 0)
+                        break;
+        }
+
+        return index;
+}
+EXPORT_SYMBOL(radix_tree_next_hole);
+
 static unsigned int
 __lookup(struct radix_tree_node *slot, void **results, unsigned long index,
         unsigned int max_items, unsigned long *next_index)