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Subject[PATCH 2.6.13] lockless pagecache 4/7
4/7

--
SUSE Labs, Novell Inc.

From: Hans Reiser <reiser@namesys.com>

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.

Index: linux-2.6/include/linux/radix-tree.h
===================================================================
--- linux-2.6.orig/include/linux/radix-tree.h
+++ linux-2.6/include/linux/radix-tree.h
@@ -46,6 +46,7 @@ do { \

int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
+void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
void *radix_tree_delete(struct radix_tree_root *, unsigned long);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
Index: linux-2.6/lib/radix-tree.c
===================================================================
--- linux-2.6.orig/lib/radix-tree.c
+++ linux-2.6/lib/radix-tree.c
@@ -276,14 +276,8 @@ int radix_tree_insert(struct radix_tree_
}
EXPORT_SYMBOL(radix_tree_insert);

-/**
- * radix_tree_lookup - perform lookup operation on a radix tree
- * @root: radix tree root
- * @index: index key
- *
- * Lookup the item at the position @index in the radix tree @root.
- */
-void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
+static inline void **__lookup_slot(struct radix_tree_root *root,
+ unsigned long index)
{
unsigned int height, shift;
struct radix_tree_node **slot;
@@ -306,7 +300,36 @@ void *radix_tree_lookup(struct radix_tre
height--;
}

- return *slot;
+ 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
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ */
+void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
+{
+ void **slot;
+
+ slot = __lookup_slot(root, index);
+ return slot != NULL ? *slot : NULL;
}
EXPORT_SYMBOL(radix_tree_lookup);
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