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.

Signed-off-by: Andrew Morton <[email protected]>
---

25-akpm/include/linux/radix-tree.h |    1

diff -puN include/linux/radix-tree.h~reiser4-radix_tree_lookup_slot include/linux/radix-tree.h


include/linux/radix-tree.h |    1 +
lib/radix-tree.c           |   41 ++++++++++++++++++++++++++++++++---------
2 files changed, 33 insertions(+), 9 deletions(-)

diff -puN include/linux/radix-tree.h~reiser4-radix_tree_lookup_slot include/linux/radix-tree.h
--- linux-2.6.11-rc1-mm1/include/linux/radix-tree.h~reiser4-radix_tree_lookup_slot      2005-01-24 18:19:15.596532403 +0300
+++ linux-2.6.11-rc1-mm1-vs/include/linux/radix-tree.h  2005-01-24 18:19:15.617533733 +0300
@@ -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,
diff -puN lib/radix-tree.c~reiser4-radix_tree_lookup_slot lib/radix-tree.c
--- linux-2.6.11-rc1-mm1/lib/radix-tree.c~reiser4-radix_tree_lookup_slot        2005-01-24 18:19:15.604532910 +0300
+++ linux-2.6.11-rc1-mm1-vs/lib/radix-tree.c    2005-01-24 18:19:15.620533923 +0300
@@ -277,14 +277,8 @@ 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;
@@ -307,7 +301,36 @@ 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);


_