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/* SPDX-License-Identifier: GPL-2.0-or-later */
Red Black Trees
(C) 1999 Andrea Arcangeli <>
To use rbtrees you'll have to implement your own insert and search cores.
This will avoid us to use callbacks and to drop drammatically performances.
I know it's not the cleaner way, but in C (not in C++) to get
performances and genericity...
See Documentation/rbtree.txt for documentation and samples.
#include <linux/kernel.h>
#include <linux/stddef.h>
struct rb_node {
unsigned long __rb_parent_color;
struct rb_node *rb_right;
struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
/* The alignment might seem pointless, but allegedly CRIS needs it */
struct rb_root {
struct rb_node *rb_node;
#define rb_parent(r) ((struct rb_node *)((r)->__rb_parent_color & ~3))
#define RB_ROOT (struct rb_root) { NULL, }
#define rb_entry(ptr, type, member) container_of(ptr, type, member)
#define RB_EMPTY_ROOT(root) (READ_ONCE((root)->rb_node) == NULL)
/* 'empty' nodes are nodes that are known not to be inserted in an rbtree */
#define RB_EMPTY_NODE(node) \
((node)->__rb_parent_color == (unsigned long)(node))
#define RB_CLEAR_NODE(node) \
((node)->__rb_parent_color = (unsigned long)(node))
extern void rb_insert_color(struct rb_node *, struct rb_root *);
extern void rb_erase(struct rb_node *, struct rb_root *);
/* Find logical next and previous nodes in a tree */
extern struct rb_node *rb_next(const struct rb_node *);
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);
static inline void rb_link_node(struct rb_node *node, struct rb_node *parent,
struct rb_node **rb_link)
node->__rb_parent_color = (unsigned long)parent;
node->rb_left = node->rb_right = NULL;
*rb_link = 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)
static inline void rb_erase_init(struct rb_node *n, struct rb_root *root)
rb_erase(n, root);
* Leftmost-cached rbtrees.
* We do not cache the rightmost node based on footprint
* size vs number of potential users that could benefit
* from O(1) rb_last(). Just not worth it, users that want
* this feature can always implement the logic explicitly.
* Furthermore, users that want to cache both pointers may
* find it a bit asymmetric, but that's ok.
struct rb_root_cached {
struct rb_root rb_root;
struct rb_node *rb_leftmost;
#define RB_ROOT_CACHED (struct rb_root_cached) { {NULL, }, NULL }
/* Same as rb_first(), but O(1) */
#define rb_first_cached(root) (root)->rb_leftmost
static inline void rb_insert_color_cached(struct rb_node *node,
struct rb_root_cached *root,
bool leftmost)
if (leftmost)
root->rb_leftmost = node;
rb_insert_color(node, &root->rb_root);
static inline void rb_erase_cached(struct rb_node *node,
struct rb_root_cached *root)
if (root->rb_leftmost == node)
root->rb_leftmost = rb_next(node);
rb_erase(node, &root->rb_root);
static inline void rb_replace_node_cached(struct rb_node *victim,
struct rb_node *new,
struct rb_root_cached *root)
if (root->rb_leftmost == victim)
root->rb_leftmost = new;
rb_replace_node(victim, new, &root->rb_root);