From 9dee5c51516d2c3fff22633c1272c5652e68075a Mon Sep 17 00:00:00 2001 From: Cody P Schafer Date: Wed, 11 Sep 2013 14:25:10 -0700 Subject: [PATCH] rbtree: add postorder iteration functions Postorder iteration yields all of a node's children prior to yielding the node itself, and this particular implementation also avoids examining the leaf links in a node after that node has been yielded. In what I expect will be its most common usage, postorder iteration allows the deletion of every node in an rbtree without modifying the rbtree nodes (no _requirement_ that they be nulled) while avoiding referencing child nodes after they have been "deleted" (most commonly, freed). I have only updated zswap to use this functionality at this point, but numerous bits of code (most notably in the filesystem drivers) use a hand rolled postorder iteration that NULLs child links as it traverses the tree. Each of those instances could be replaced with this common implementation. 1 & 2 add rbtree postorder iteration functions. 3 adds testing of the iteration to the rbtree runtime tests 4 allows building the rbtree runtime tests as builtins 5 updates zswap. This patch: Add postorder iteration functions for rbtree. These are useful for safely freeing an entire rbtree without modifying the tree at all. Signed-off-by: Cody P Schafer Reviewed-by: Seth Jennings Cc: David Woodhouse Cc: Rik van Riel Cc: Michel Lespinasse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/rbtree.h | 4 ++++ lib/rbtree.c | 40 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+) diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h index 0022c1bb1e26..c467151e9950 100644 --- a/include/linux/rbtree.h +++ b/include/linux/rbtree.h @@ -68,6 +68,10 @@ extern struct rb_node *rb_prev(const struct rb_node *); extern struct rb_node *rb_first(const struct rb_root *); extern struct rb_node *rb_last(const 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 *); + /* 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/lib/rbtree.c b/lib/rbtree.c index c0e31fe2fabf..65f4effd117f 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -518,3 +518,43 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new, *new = *victim; } EXPORT_SYMBOL(rb_replace_node); + +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; +} +EXPORT_SYMBOL(rb_next_postorder); + +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); +} +EXPORT_SYMBOL(rb_first_postorder); -- GitLab