radix-tree: add radix_tree_gang_lookup_index

Add radix_tree_gang_lookup_index to get the radix tree
indices along with the pointers. This will be  helpful,
for e.g. if a radix_tree_delete has to be performed
depending on one of the result values.

Change-Id: Iab83d027968462aa30da5341fa3f60134b6c1137
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

include/linux/radix-tree.h

@@ -274,6 +274,10 @@ 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 int
+radix_tree_gang_lookup_index(struct radix_tree_root *root, void **results,
+			unsigned long *indices, unsigned long first_index,
+			unsigned int max_items);
 unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
 			void ***results, unsigned long *indices,
 			unsigned long first_index, unsigned int max_items);

lib/radix-tree.c

@@ -1034,6 +1034,49 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 }
 EXPORT_SYMBOL(radix_tree_gang_lookup);
 
+/**
+ *	radix_tree_gang_lookup_index - perform multiple lookup on a radix tree
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@indices:	where their indices should be placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *
+ *	Performs an index-ascending scan of the tree for present items.  Places
+ *	them at *@results and returns the number of items which were placed at
+ *	*@results. The indices are placed in @indices.
+ *
+ *	The implementation is naive.
+ *
+ *	Just one difference from radix_tree_gang_lookup, the indices are also
+ *	collected along with the results of lookup.
+ */
+unsigned int
+radix_tree_gang_lookup_index(struct radix_tree_root *root, void **results,
+			unsigned long *indices, unsigned long first_index,
+			unsigned int max_items)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_slot(slot, root, &iter, first_index) {
+		results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot));
+		if (!results[ret])
+			continue;
+		if (indices)
+			indices[ret] = iter.index;
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_index);
+
 /**
  *	radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
  *	@root:		radix tree root