[PATCH] reiser4: add radix_tree_lookup_slot()
Reiser4 uses radix trees to solve a trouble reiser4_readdir has serving nfs
requests.
Unfortunately, radix tree api lacks an operation suitable for modifying
existing entry. This patch adds radix_tree_lookup_slot which returns pointer
to found item within the tree. That location can be then updated.
Both Nick and Christoph Lameter have patches which need this as well.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index d1c057e7..88511c3 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -281,6 +281,47 @@
}
EXPORT_SYMBOL(radix_tree_insert);
+static inline void **__lookup_slot(struct radix_tree_root *root,
+ unsigned long index)
+{
+ unsigned int height, shift;
+ struct radix_tree_node **slot;
+
+ height = root->height;
+ if (index > radix_tree_maxindex(height))
+ return NULL;
+
+ shift = (height-1) * RADIX_TREE_MAP_SHIFT;
+ slot = &root->rnode;
+
+ while (height > 0) {
+ if (*slot == NULL)
+ return NULL;
+
+ slot = (struct radix_tree_node **)
+ ((*slot)->slots +
+ ((index >> shift) & RADIX_TREE_MAP_MASK));
+ shift -= RADIX_TREE_MAP_SHIFT;
+ height--;
+ }
+
+ return (void **)slot;
+}
+
+/**
+ * radix_tree_lookup_slot - lookup a slot in a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Lookup the slot corresponding to the position @index in the radix tree
+ * @root. This is useful for update-if-exists operations.
+ */
+void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
+{
+ return __lookup_slot(root, index);
+}
+EXPORT_SYMBOL(radix_tree_lookup_slot);
+
/**
* radix_tree_lookup - perform lookup operation on a radix tree
* @root: radix tree root
@@ -290,26 +331,10 @@
*/
void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
{
- unsigned int height, shift;
- struct radix_tree_node *slot;
+ void **slot;
- height = root->height;
- if (index > radix_tree_maxindex(height))
- return NULL;
-
- shift = (height-1) * RADIX_TREE_MAP_SHIFT;
- slot = root->rnode;
-
- while (height > 0) {
- if (slot == NULL)
- return NULL;
-
- slot = slot->slots[(index >> shift) & RADIX_TREE_MAP_MASK];
- shift -= RADIX_TREE_MAP_SHIFT;
- height--;
- }
-
- return slot;
+ slot = __lookup_slot(root, index);
+ return slot != NULL ? *slot : NULL;
}
EXPORT_SYMBOL(radix_tree_lookup);