3 files changed, 106 insertions, 5 deletions

diff --git a/Documentation/rbtree.txt b/Documentation/rbtree.txt
index aae8355d3166..221f38be98f4 100644
--- a/Documentation/rbtree.txt
+++ b/Documentation/rbtree.txt
@@ -190,3 +190,61 @@ Example:
   for (node = rb_first(&mytree); node; node = rb_next(node))
         printk("key=%s\n", rb_entry(node, struct mytype, node)->keystring);
 
+Support for Augmented rbtrees
+-----------------------------
+
+Augmented rbtree is an rbtree with "some" additional data stored in each node.
+This data can be used to augment some new functionality to rbtree.
+Augmented rbtree is an optional feature built on top of basic rbtree
+infrastructure. rbtree user who wants this feature will have an augment
+callback function in rb_root initialized.
+
+This callback function will be called from rbtree core routines whenever
+a node has a change in one or both of its children. It is the responsibility
+of the callback function to recalculate the additional data that is in the
+rb node using new children information. Note that if this new additional
+data affects the parent node's additional data, then callback function has
+to handle it and do the recursive updates.
+
+
+Interval tree is an example of augmented rb tree. Reference -
+"Introduction to Algorithms" by Cormen, Leiserson, Rivest and Stein.
+More details about interval trees:
+
+Classical rbtree has a single key and it cannot be directly used to store
+interval ranges like [lo:hi] and do a quick lookup for any overlap with a new
+lo:hi or to find whether there is an exact match for a new lo:hi.
+
+However, rbtree can be augmented to store such interval ranges in a structured
+way making it possible to do efficient lookup and exact match.
+
+This "extra information" stored in each node is the maximum hi
+(max_hi) value among all the nodes that are its descendents. This
+information can be maintained at each node just be looking at the node
+and its immediate children. And this will be used in O(log n) lookup
+for lowest match (lowest start address among all possible matches)
+with something like:
+
+find_lowest_match(lo, hi, node)
+{
+        lowest_match = NULL;
+        while (node) {
+                if (max_hi(node->left) > lo) {
+                        // Lowest overlap if any must be on left side
+                        node = node->left;
+                } else if (overlap(lo, hi, node)) {
+                        lowest_match = node;
+                        break;
+                } else if (lo > node->lo) {
+                        // Lowest overlap if any must be on right side
+                        node = node->right;
+                } else {
+                        break;
+                }
+        }
+        return lowest_match;
+}
+
+Finding exact match will be to first find lowest match and then to follow
+successor nodes looking for exact match, until the start of a node is beyond
+the hi value we are looking for.
diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index 9c295411d01f..8e33a256ea0e 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -110,6 +110,7 @@ struct rb_node
 struct rb_root
 {
         struct rb_node *rb_node;
+        void (*augment_cb)(struct rb_node *node);
 };
 
 
@@ -129,7 +130,9 @@ static inline void rb_set_color(struct rb_node *rb, int color)
         rb->rb_parent_color = (rb->rb_parent_color & ~1) | color;
 }
 
-#define RB_ROOT (struct rb_root) { NULL, }
+#define RB_ROOT (struct rb_root) { NULL, NULL, }
+#define RB_AUGMENT_ROOT(x)      (struct rb_root) { NULL, x}
+
 #define rb_entry(ptr, type, member) container_of(ptr, type, member)
 
 #define RB_EMPTY_ROOT(root)     ((root)->rb_node == NULL)
diff --git a/lib/rbtree.c b/lib/rbtree.c
index e2aa3be29858..15e10b1afdd2 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -44,6 +44,11 @@ static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)
         else
                 root->rb_node = right;
         rb_set_parent(node, right);
+
+        if (root->augment_cb) {
+                root->augment_cb(node);
+                root->augment_cb(right);
+        }
 }
 
 static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
@@ -67,12 +72,20 @@ static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
         else
                 root->rb_node = left;
         rb_set_parent(node, left);
+
+        if (root->augment_cb) {
+                root->augment_cb(node);
+                root->augment_cb(left);
+        }
 }
 
 void rb_insert_color(struct rb_node *node, struct rb_root *root)
 {
         struct rb_node *parent, *gparent;
 
+        if (root->augment_cb)
+                root->augment_cb(node);
+
         while ((parent = rb_parent(node)) && rb_is_red(parent))
         {
                 gparent = rb_parent(parent);
@@ -227,12 +240,15 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
         else
         {
                 struct rb_node *old = node, *left;
+                int old_parent_cb = 0;
+                int successor_parent_cb = 0;
 
                 node = node->rb_right;
                 while ((left = node->rb_left) != NULL)
                         node = left;
 
                 if (rb_parent(old)) {
+                        old_parent_cb = 1;
                         if (rb_parent(old)->rb_left == old)
                                 rb_parent(old)->rb_left = node;
                         else
@@ -247,8 +263,10 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
                 if (parent == old) {
                         parent = node;
                 } else {
+                        successor_parent_cb = 1;
                         if (child)
                                 rb_set_parent(child, parent);
+
                         parent->rb_left = child;
 
                         node->rb_right = old->rb_right;
@@ -259,6 +277,24 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
                 node->rb_left = old->rb_left;
                 rb_set_parent(old->rb_left, node);
 
+                if (root->augment_cb) {
+                        /*
+                         * Here, three different nodes can have new children.
+                         * The parent of the successor node that was selected
+                         * to replace the node to be erased.
+                         * The node that is getting erased and is now replaced
+                         * by its successor.
+                         * The parent of the node getting erased-replaced.
+                         */
+                        if (successor_parent_cb)
+                                root->augment_cb(parent);
+
+                        root->augment_cb(node);
+
+                        if (old_parent_cb)
+                                root->augment_cb(rb_parent(old));
+                }
+
                 goto color;
         }
 
@@ -267,15 +303,19 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
 
         if (child)
                 rb_set_parent(child, parent);
-        if (parent)
-        {
+
+        if (parent) {
                 if (parent->rb_left == node)
                         parent->rb_left = child;
                 else
                         parent->rb_right = child;
-        }
-        else
+
+                if (root->augment_cb)
+                        root->augment_cb(parent);
+
+        } else {
                 root->rb_node = child;
+        }
 
  color:
         if (color == RB_BLACK)