ion: index client->handles rbtree by buffer

The only remaining users of the client->handles rbtree are
iterating through it like a list.  Keep the rbtree, but change
its index to be the buffer address instead of the handle address,
which makes ion_handle_lookup a fast rbtree search.

Signed-off-by: Colin Cross <ccross@android.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -388,13 +388,16 @@ static int ion_handle_put(struct ion_handle *handle)
 static struct ion_handle *ion_handle_lookup(struct ion_client *client,
 					    struct ion_buffer *buffer)
 {
-	struct rb_node *n;
-
-	for (n = rb_first(&client->handles); n; n = rb_next(n)) {
-		struct ion_handle *handle = rb_entry(n, struct ion_handle,
-						   node);
-		if (handle->buffer == buffer)
-			return handle;
+	struct rb_node *n = client->handles.rb_node;
+
+	while (n) {
+		struct ion_handle *entry = rb_entry(n, struct ion_handle, node);
+		if (buffer < entry->buffer)
+			n = n->rb_left;
+		else if (buffer > entry->buffer)
+			n = n->rb_right;
+		else
+			return entry;
 	}
 	return ERR_PTR(-EINVAL);
 }
@@ -432,9 +435,9 @@ static int ion_handle_add(struct ion_client *client, struct ion_handle *handle)
 		parent = *p;
 		entry = rb_entry(parent, struct ion_handle, node);
 
-		if (handle < entry)
+		if (handle->buffer < entry->buffer)
 			p = &(*p)->rb_left;
-		else if (handle > entry)
+		else if (handle->buffer > entry->buffer)
 			p = &(*p)->rb_right;
 		else
 			WARN(1, "%s: buffer already found.", __func__);