[RFC PATCH mtd-utils 018/110] mtd-utils: Extract rbtree implementation to common lib

[Zhihao Cheng]

Current rbtree implementation code is put under jffs utils, extract it
into common lib, and add more rbtree operations(eg. rb_first_postorder,
rb_next_postorder, etc.).

This is a preparation for replacing implementation of UBIFS utils with
linux kernel libs.

Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
 {jffsX-utils => include}/rbtree.h | 32 ++++++++++++++++++++++++++++++++
 jffsX-utils/Makemodule.am         |  6 ++----
 lib/Makemodule.am                 |  2 ++
 {jffsX-utils => lib}/rbtree.c     | 38 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 74 insertions(+), 4 deletions(-)
 rename {jffsX-utils => include}/rbtree.h (79%)
 rename {jffsX-utils => lib}/rbtree.c (90%)

diff --git a/jffsX-utils/rbtree.h b/include/rbtree.h
similarity index 79%
rename from jffsX-utils/rbtree.h
rename to include/rbtree.h
index 0d77b65f..89926e74 100644
--- a/jffsX-utils/rbtree.h
+++ b/include/rbtree.h
@@ -155,6 +155,38 @@ extern struct rb_node *rb_prev(struct rb_node *);
 extern struct rb_node *rb_first(struct rb_root *);
 extern struct rb_node *rb_last(struct rb_root *);
 
+/* Postorder iteration - always visit the parent after its children */
+extern struct rb_node *rb_first_postorder(const struct rb_root *);
+extern struct rb_node *rb_next_postorder(const struct rb_node *);
+
+#define rb_entry_safe(ptr, type, member) \
+	({ typeof(ptr) ____ptr = (ptr); \
+	   ____ptr ? rb_entry(____ptr, type, member) : NULL; \
+	})
+
+/**
+ * rbtree_postorder_for_each_entry_safe - iterate in post-order over rb_root of
+ * given type allowing the backing memory of @pos to be invalidated
+ *
+ * @pos:	the 'type *' to use as a loop cursor.
+ * @n:		another 'type *' to use as temporary storage
+ * @root:	'rb_root *' of the rbtree.
+ * @field:	the name of the rb_node field within 'type'.
+ *
+ * rbtree_postorder_for_each_entry_safe() provides a similar guarantee as
+ * list_for_each_entry_safe() and allows the iteration to continue independent
+ * of changes to @pos by the body of the loop.
+ *
+ * Note, however, that it cannot handle other modifications that re-order the
+ * rbtree it is iterating over. This includes calling rb_erase() on @pos, as
+ * rb_erase() may rebalance the tree, causing us to miss some nodes.
+ */
+#define rbtree_postorder_for_each_entry_safe(pos, n, root, field) \
+	for (pos = rb_entry_safe(rb_first_postorder(root), typeof(*pos), field); \
+	     pos && ({ n = rb_entry_safe(rb_next_postorder(&pos->field), \
+			typeof(*pos), field); 1; }); \
+	     pos = n)
+
 /* Fast replacement of a single node without remove/rebalance/add/rebalance */
 extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
 			    struct rb_root *root);
diff --git a/jffsX-utils/Makemodule.am b/jffsX-utils/Makemodule.am
index 2374b858..4ae4c57b 100644
--- a/jffsX-utils/Makemodule.am
+++ b/jffsX-utils/Makemodule.am
@@ -1,16 +1,14 @@
 mkfs_jffs2_SOURCES = \
 	jffsX-utils/mkfs.jffs2.c \
-	jffsX-utils/rbtree.h \
 	jffsX-utils/compr.h \
-	jffsX-utils/rbtree.c \
 	jffsX-utils/compr.c \
 	jffsX-utils/compr_rtime.c \
 	jffsX-utils/compr.h \
-	jffsX-utils/rbtree.h \
 	jffsX-utils/summary.h \
 	include/linux/jffs2.h \
 	include/mtd/jffs2-user.h \
-	include/list.h
+	include/list.h \
+	include/rbtree.h
 mkfs_jffs2_LDADD = libmtd.a $(ZLIB_LIBS) $(LZO_LIBS)
 mkfs_jffs2_CPPFLAGS = $(AM_CPPFLAGS) $(ZLIB_CFLAGS) $(LZO_CFLAGS)
 
diff --git a/lib/Makemodule.am b/lib/Makemodule.am
index 7f890daa..441532de 100644
--- a/lib/Makemodule.am
+++ b/lib/Makemodule.am
@@ -7,6 +7,8 @@ libmtd_a_SOURCES = \
 	include/common.h \
 	lib/list_sort.c \
 	include/list.h \
+	lib/rbtree.c \
+	include/rbtree.h \
 	lib/libcrc32.c \
 	include/crc32.h \
 	lib/libmtd_legacy.c \
diff --git a/jffsX-utils/rbtree.c b/lib/rbtree.c
similarity index 90%
rename from jffsX-utils/rbtree.c
rename to lib/rbtree.c
index 329e0986..32c87556 100644
--- a/jffsX-utils/rbtree.c
+++ b/lib/rbtree.c
@@ -388,3 +388,41 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new,
 	/* Copy the pointers/colour from the victim to the replacement */
 	*new = *victim;
 }
+
+static struct rb_node *rb_left_deepest_node(const struct rb_node *node)
+{
+	for (;;) {
+		if (node->rb_left)
+			node = node->rb_left;
+		else if (node->rb_right)
+			node = node->rb_right;
+		else
+			return (struct rb_node *)node;
+	}
+}
+
+struct rb_node *rb_next_postorder(const struct rb_node *node)
+{
+	const struct rb_node *parent;
+	if (!node)
+		return NULL;
+	parent = rb_parent(node);
+
+	/* If we're sitting on node, we've already seen our children */
+	if (parent && node == parent->rb_left && parent->rb_right) {
+		/* If we are the parent's left node, go to the parent's right
+		 * node then all the way down to the left */
+		return rb_left_deepest_node(parent->rb_right);
+	} else
+		/* Otherwise we are the parent's right node, and the parent
+		 * should be next */
+		return (struct rb_node *)parent;
+}
+
+struct rb_node *rb_first_postorder(const struct rb_root *root)
+{
+	if (!root->rb_node)
+		return NULL;
+
+	return rb_left_deepest_node(root->rb_node);
+}
-- 
2.13.6