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From:   Davidlohr Bueso <dave@stgolabs.net>
To:     akpm@linux-foundation.org
Cc:     walken@google.com, peterz@infradead.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org,
        dave@stgolabs.net, Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH 02/11] lib/interval-tree: add an equivalent tree with [a,b) intervals
Date:   Thu,  3 Oct 2019 13:18:49 -0700
Message-Id: <20191003201858.11666-3-dave@stgolabs.net>
In-Reply-To: <20191003201858.11666-1-dave@stgolabs.net>
References: <20191003201858.11666-1-dave@stgolabs.net>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

While the kernel's interval tree implementation uses closed intervals, all
users (with the exception of query stabbing) really want half closed intervals,
specifically [a, b), and will explicitly correct this before calling the tree api.

This patch simply duplicates the include/linuxinterval_tree_generic.h header into
a interval_tree_gen.h (gen as in 'generic' and 'generate' :-) with two differences:

- The 'last' endpoint is renamed 'end'; this is something lib/interval_tree.c will
also need to update, but that is later in the series.

- The lookup calls have been adapted accordingly, such that users need not need to
do the subtraction by one fixup.

No users are ported over in this patch.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 include/linux/interval_tree_gen.h | 179 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)
 create mode 100644 include/linux/interval_tree_gen.h

diff --git a/include/linux/interval_tree_gen.h b/include/linux/interval_tree_gen.h
new file mode 100644
index 000000000000..5d446c0bd89a
--- /dev/null
+++ b/include/linux/interval_tree_gen.h
@@ -0,0 +1,179 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+  Interval Trees
+  (C) 2012  Michel Lespinasse <walken@google.com>
+*/
+
+#include <linux/rbtree_augmented.h>
+
+/*
+ * Template for implementing interval trees
+ *
+ * ITSTRUCT:   struct type of the interval tree nodes
+ * ITRB:       name of struct rb_node field within ITSTRUCT
+ * ITTYPE:     type of the interval endpoints
+ * ITSUBTREE:  name of ITTYPE field within ITSTRUCT holding end-in-subtree
+ * ITSTART(n): start endpoint of ITSTRUCT node n
+ * ITEND(n):   end/last endpoint of ITSTRUCT node n
+ * ITSTATIC:   'static' or empty
+ * ITPREFIX:   prefix to use for the inline tree definitions
+ *
+ * Note - before using this, please consider if generic version
+ * (interval_tree.h) would work for you...
+ */
+
+#define INTERVAL_TREE_DEFINE(ITSTRUCT, ITRB, ITTYPE, ITSUBTREE,		      \
+			     ITSTART, ITEND, ITSTATIC, ITPREFIX)	      \
+									      \
+/* Callbacks for augmented rbtree insert and remove */			      \
+									      \
+RB_DECLARE_CALLBACKS_MAX(static, ITPREFIX ## _augment,			      \
+			 ITSTRUCT, ITRB, ITTYPE, ITSUBTREE, ITEND)	      \
+									      \
+/* Insert / remove interval nodes from the tree */			      \
+									      \
+ITSTATIC void ITPREFIX ## _insert(ITSTRUCT *node,			      \
+				  struct rb_root_cached *root)		      \
+{									      \
+	struct rb_node **link = &root->rb_root.rb_node, *rb_parent = NULL;    \
+	ITTYPE start = ITSTART(node), end = ITEND(node);		      \
+	ITSTRUCT *parent;						      \
+	bool leftmost = true;						      \
+									      \
+	while (*link) {							      \
+		rb_parent = *link;					      \
+		parent = rb_entry(rb_parent, ITSTRUCT, ITRB);		      \
+		if (parent->ITSUBTREE < end)				      \
+			parent->ITSUBTREE = end;			      \
+		if (start < ITSTART(parent))				      \
+			link = &parent->ITRB.rb_left;			      \
+		else {							      \
+			link = &parent->ITRB.rb_right;			      \
+			leftmost = false;				      \
+		}							      \
+	}								      \
+									      \
+	node->ITSUBTREE = end;						      \
+	rb_link_node(&node->ITRB, rb_parent, link);			      \
+	rb_insert_augmented_cached(&node->ITRB, root,			      \
+				   leftmost, &ITPREFIX ## _augment);	      \
+}									      \
+									      \
+ITSTATIC void ITPREFIX ## _remove(ITSTRUCT *node,			      \
+				  struct rb_root_cached *root)		      \
+{									      \
+	rb_erase_augmented_cached(&node->ITRB, root, &ITPREFIX ## _augment);  \
+}									      \
+									      \
+/*									      \
+ * Iterate over intervals intersecting [start;end)			      \
+ *									      \
+ * Note that a node's interval intersects [start;end) iff:		      \
+ *   Cond1: ITSTART(node) < end						      \
+ * and									      \
+ *   Cond2: start < ITEND(node)						      \
+ */									      \
+									      \
+static ITSTRUCT *							      \
+ITPREFIX ## _subtree_search(ITSTRUCT *node, ITTYPE start, ITTYPE end)	      \
+{									      \
+	while (true) {							      \
+		/*							      \
+		 * Loop invariant: start <= node->ITSUBTREE		      \
+		 * (Cond2 is satisfied by one of the subtree nodes)	      \
+		 */							      \
+		if (node->ITRB.rb_left) {				      \
+			ITSTRUCT *left = rb_entry(node->ITRB.rb_left,	      \
+						  ITSTRUCT, ITRB);	      \
+			if (start < left->ITSUBTREE) {			      \
+				/*					      \
+				 * Some nodes in left subtree satisfy Cond2.  \
+				 * Iterate to find the leftmost such node N.  \
+				 * If it also satisfies Cond1, that's the     \
+				 * match we are looking for. Otherwise, there \
+				 * is no matching interval as nodes to the    \
+				 * right of N can't satisfy Cond1 either.     \
+				 */					      \
+				node = left;				      \
+				continue;				      \
+			}						      \
+		}							      \
+		if (ITSTART(node) < end) {		/* Cond1 */	      \
+			if (start < ITEND(node))	/* Cond2 */	      \
+				return node;	/* node is leftmost match */  \
+			if (node->ITRB.rb_right) {			      \
+				node = rb_entry(node->ITRB.rb_right,	      \
+						ITSTRUCT, ITRB);	      \
+				if (start <= node->ITSUBTREE)		      \
+					continue;			      \
+			}						      \
+		}							      \
+		return NULL;	/* No match */				      \
+	}								      \
+}									      \
+									      \
+ITSTATIC ITSTRUCT *							      \
+ITPREFIX ## _iter_first(struct rb_root_cached *root,			      \
+			ITTYPE start, ITTYPE end)			      \
+{									      \
+	ITSTRUCT *node, *leftmost;					      \
+									      \
+	if (!root->rb_root.rb_node)					      \
+		return NULL;						      \
+									      \
+	/*								      \
+	 * Fastpath range intersection/overlap where we compare the	      \
+	 * smallest 'start' and largest 'end' in the tree. For the latter,    \
+	 * we rely on the root node, which by augmented interval tree	      \
+	 * property, holds the largest value in its end-in-subtree.	      \
+	 * This allows mitigating some of the tree walk overhead for	      \
+	 * for non-intersecting ranges, maintained and consulted in O(1).     \
+	 */								      \
+	node = rb_entry(root->rb_root.rb_node, ITSTRUCT, ITRB);		      \
+	if (node->ITSUBTREE <= start)	/* !Cond2 */			      \
+		return NULL;						      \
+									      \
+	leftmost = rb_entry(root->rb_leftmost, ITSTRUCT, ITRB);		      \
+	if (ITSTART(leftmost) >= end)	/* !Cond1 */			      \
+		return NULL;						      \
+									      \
+	return ITPREFIX ## _subtree_search(node, start, end);		      \
+}									      \
+									      \
+ITSTATIC ITSTRUCT *							      \
+ITPREFIX ## _iter_next(ITSTRUCT *node, ITTYPE start, ITTYPE end)	      \
+{									      \
+	struct rb_node *rb = node->ITRB.rb_right, *prev;		      \
+									      \
+	while (true) {							      \
+		/*							      \
+		 * Loop invariants:					      \
+		 *   Cond1: ITSTART(node) < end				      \
+		 *   rb == node->ITRB.rb_right				      \
+		 *							      \
+		 * First, search right subtree if suitable		      \
+		 */							      \
+		if (rb) {						      \
+			ITSTRUCT *right = rb_entry(rb, ITSTRUCT, ITRB);	      \
+			if (start < right->ITSUBTREE)			      \
+				return ITPREFIX ## _subtree_search(right,     \
+								start, end); \
+		}							      \
+									      \
+		/* Move up the tree until we come from a node's left child */ \
+		do {							      \
+			rb = rb_parent(&node->ITRB);			      \
+			if (!rb)					      \
+				return NULL;				      \
+			prev = &node->ITRB;				      \
+			node = rb_entry(rb, ITSTRUCT, ITRB);		      \
+			rb = node->ITRB.rb_right;			      \
+		} while (prev == rb);					      \
+									      \
+		/* Check if the node intersects [start;end) */		      \
+		if (end <= ITSTART(node))		/* !Cond1 */	      \
+			return NULL;					      \
+		else if (start < ITEND(node))		/* Cond2 */	      \
+			return node;					      \
+	}								      \
+}
-- 
2.16.4