lib/timerqueue.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Generic Timer-queue
   4  *
   5  *  Manages a simple queue of timers, ordered by expiration time.
   6  *  Uses rbtrees for quick list adds and expiration.
   7  *
   8  *  NOTE: All of the following functions need to be serialized
   9  *  to avoid races. No locking is done by this library code.
  10  */
  11
  12 #include <linux/bug.h>
  13 #include <linux/timerqueue.h>
  14 #include <linux/rbtree.h>
  15 #include <linux/export.h>
  16
  17 #define __node_2_tq(_n) \
  18         rb_entry((_n), struct timerqueue_node, node)
  19
  20 static inline bool __timerqueue_less(struct rb_node *a, const struct rb_node *b)
  21 {
  22         return __node_2_tq(a)->expires < __node_2_tq(b)->expires;
  23 }
  24
  25 /**
  26  * timerqueue_add - Adds timer to timerqueue.
  27  *
  28  * @head: head of timerqueue
  29  * @node: timer node to be added
  30  *
  31  * Adds the timer node to the timerqueue, sorted by the node's expires
  32  * value. Returns true if the newly added timer is the first expiring timer in
  33  * the queue.
  34  */
  35 bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
  36 {
  37         /* Make sure we don't add nodes that are already added */
  38         WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
  39
  40         return rb_add_cached(&node->node, &head->rb_root, __timerqueue_less);
  41 }
  42 EXPORT_SYMBOL_GPL(timerqueue_add);
  43
  44 /**
  45  * timerqueue_del - Removes a timer from the timerqueue.
  46  *
  47  * @head: head of timerqueue
  48  * @node: timer node to be removed
  49  *
  50  * Removes the timer node from the timerqueue. Returns true if the queue is
  51  * not empty after the remove.
  52  */
  53 bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
  54 {
  55         WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
  56
  57         rb_erase_cached(&node->node, &head->rb_root);
  58         RB_CLEAR_NODE(&node->node);
  59
  60         return !RB_EMPTY_ROOT(&head->rb_root.rb_root);
  61 }
  62 EXPORT_SYMBOL_GPL(timerqueue_del);
  63
  64 /**
  65  * timerqueue_iterate_next - Returns the timer after the provided timer
  66  *
  67  * @node: Pointer to a timer.
  68  *
  69  * Provides the timer that is after the given node. This is used, when
  70  * necessary, to iterate through the list of timers in a timer list
  71  * without modifying the list.
  72  */
  73 struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
  74 {
  75         struct rb_node *next;
  76
  77         if (!node)
  78                 return NULL;
  79         next = rb_next(&node->node);
  80         if (!next)
  81                 return NULL;
  82         return container_of(next, struct timerqueue_node, node);
  83 }
  84 EXPORT_SYMBOL_GPL(timerqueue_iterate_next);