[PATCH 09/30] radix-tree: Add missing sibling entry functionality

[Matthew Wilcox]

The code I previously added to enable multiorder radix tree entries was
untested and hence buggy.  This commit adds the support functions that
Ross and I decided were necessary over a four-week period of iterating
various designs.

Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 lib/radix-tree.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index ae53ad56e01e..40343f28a705 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -80,6 +80,46 @@ static inline void *indirect_to_ptr(void *ptr)
 	return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
 }
 
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+/* Sibling slots point directly to another slot in the same node */
+static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
+{
+	void **ptr = node;
+	return (parent->slots <= ptr) &&
+			(ptr < parent->slots + RADIX_TREE_MAP_SIZE);
+}
+#else
+static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
+{
+	return false;
+}
+#endif
+
+static inline unsigned get_sibling_offset(struct radix_tree_node *parent,
+						 void **slot)
+{
+	return slot - parent->slots;
+}
+
+static unsigned radix_tree_descend(struct radix_tree_node *parent,
+				struct radix_tree_node **nodep, unsigned offset)
+{
+	void **entry = rcu_dereference_raw(parent->slots[offset]);
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+	if (radix_tree_is_indirect_ptr(entry)) {
+		uintptr_t siboff = entry - parent->slots;
+		if (siboff < RADIX_TREE_MAP_SIZE) {
+			offset = siboff;
+			entry = rcu_dereference_raw(parent->slots[offset]);
+		}
+	}
+#endif
+
+	*nodep = (void *)entry;
+	return offset;
+}
+
 static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
 {
 	return root->gfp_mask & __GFP_BITS_MASK;
-- 
2.8.0.rc3