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