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 /**
  18  * timerqueue_add - Adds timer to timerqueue.
  19  *
  20  * @head: head of timerqueue
  21  * @node: timer node to be added
  22  *
  23  * Adds the timer node to the timerqueue, sorted by the node's expires
  24  * value. Returns true if the newly added timer is the first expiring timer in
  25  * the queue.
  26  */
  27 bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
  28 {
  29         struct rb_node **p = &head->head.rb_node;
  30         struct rb_node *parent = NULL;
  31         struct timerqueue_node  *ptr;
  32
  33         /* Make sure we don't add nodes that are already added */
  34         WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
  35
  36         while (*p) {
  37                 parent = *p;
  38                 ptr = rb_entry(parent, struct timerqueue_node, node);
  39                 if (node->expires < ptr->expires)
  40                         p = &(*p)->rb_left;
  41                 else
  42                         p = &(*p)->rb_right;
  43         }
  44         rb_link_node(&node->node, parent, p);
  45         rb_insert_color(&node->node, &head->head);
  46
  47         if (!head->next || node->expires < head->next->expires) {
  48                 head->next = node;
  49                 return true;
  50         }
  51         return false;
  52 }
  53 EXPORT_SYMBOL_GPL(timerqueue_add);
  54
  55 /**
  56  * timerqueue_del - Removes a timer from the timerqueue.
  57  *
  58  * @head: head of timerqueue
  59  * @node: timer node to be removed
  60  *
  61  * Removes the timer node from the timerqueue. Returns true if the queue is
  62  * not empty after the remove.
  63  */
  64 bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
  65 {
  66         WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
  67
  68         /* update next pointer */
  69         if (head->next == node) {
  70                 struct rb_node *rbn = rb_next(&node->node);
  71
  72                 head->next = rb_entry_safe(rbn, struct timerqueue_node, node);
  73         }
  74         rb_erase(&node->node, &head->head);
  75         RB_CLEAR_NODE(&node->node);
  76         return head->next != NULL;
  77 }
  78 EXPORT_SYMBOL_GPL(timerqueue_del);
  79
  80 /**
  81  * timerqueue_iterate_next - Returns the timer after the provided timer
  82  *
  83  * @node: Pointer to a timer.
  84  *
  85  * Provides the timer that is after the given node. This is used, when
  86  * necessary, to iterate through the list of timers in a timer list
  87  * without modifying the list.
  88  */
  89 struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
  90 {
  91         struct rb_node *next;
  92
  93         if (!node)
  94                 return NULL;
  95         next = rb_next(&node->node);
  96         if (!next)
  97                 return NULL;
  98         return container_of(next, struct timerqueue_node, node);
  99 }
 100 EXPORT_SYMBOL_GPL(timerqueue_iterate_next);