lib/timerqueue.c

   1 /*
   2  *  Generic Timer-queue
   3  *
   4  *  Manages a simple queue of timers, ordered by expiration time.
   5  *  Uses rbtrees for quick list adds and expiration.
   6  *
   7  *  NOTE: All of the following functions need to be serialized
   8  *  to avoid races. No locking is done by this library code.
   9  *
  10  *  This program is free software; you can redistribute it and/or modify
  11  *  it under the terms of the GNU General Public License as published by
  12  *  the Free Software Foundation; either version 2 of the License, or
  13  *  (at your option) any later version.
  14  *
  15  *  This program is distributed in the hope that it will be useful,
  16  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  *  GNU General Public License for more details.
  19  *
  20  *  You should have received a copy of the GNU General Public License
  21  *  along with this program; if not, write to the Free Software
  22  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  23  */
  24
  25 #include <linux/bug.h>
  26 #include <linux/timerqueue.h>
  27 #include <linux/rbtree.h>
  28 #include <linux/export.h>
  29
  30 /**
  31  * timerqueue_add - Adds timer to timerqueue.
  32  *
  33  * @head: head of timerqueue
  34  * @node: timer node to be added
  35  *
  36  * Adds the timer node to the timerqueue, sorted by the node's expires
  37  * value. Returns true if the newly added timer is the first expiring timer in
  38  * the queue.
  39  */
  40 bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
  41 {
  42         struct rb_node **p = &head->head.rb_node;
  43         struct rb_node *parent = NULL;
  44         struct timerqueue_node  *ptr;
  45
  46         /* Make sure we don't add nodes that are already added */
  47         WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
  48
  49         while (*p) {
  50                 parent = *p;
  51                 ptr = rb_entry(parent, struct timerqueue_node, node);
  52                 if (node->expires < ptr->expires)
  53                         p = &(*p)->rb_left;
  54                 else
  55                         p = &(*p)->rb_right;
  56         }
  57         rb_link_node(&node->node, parent, p);
  58         rb_insert_color(&node->node, &head->head);
  59
  60         if (!head->next || node->expires < head->next->expires) {
  61                 head->next = node;
  62                 return true;
  63         }
  64         return false;
  65 }
  66 EXPORT_SYMBOL_GPL(timerqueue_add);
  67
  68 /**
  69  * timerqueue_del - Removes a timer from the timerqueue.
  70  *
  71  * @head: head of timerqueue
  72  * @node: timer node to be removed
  73  *
  74  * Removes the timer node from the timerqueue. Returns true if the queue is
  75  * not empty after the remove.
  76  */
  77 bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
  78 {
  79         WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
  80
  81         /* update next pointer */
  82         if (head->next == node) {
  83                 struct rb_node *rbn = rb_next(&node->node);
  84
  85                 head->next = rb_entry_safe(rbn, struct timerqueue_node, node);
  86         }
  87         rb_erase(&node->node, &head->head);
  88         RB_CLEAR_NODE(&node->node);
  89         return head->next != NULL;
  90 }
  91 EXPORT_SYMBOL_GPL(timerqueue_del);
  92
  93 /**
  94  * timerqueue_iterate_next - Returns the timer after the provided timer
  95  *
  96  * @node: Pointer to a timer.
  97  *
  98  * Provides the timer that is after the given node. This is used, when
  99  * necessary, to iterate through the list of timers in a timer list
 100  * without modifying the list.
 101  */
 102 struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
 103 {
 104         struct rb_node *next;
 105
 106         if (!node)
 107                 return NULL;
 108         next = rb_next(&node->node);
 109         if (!next)
 110                 return NULL;
 111         return container_of(next, struct timerqueue_node, node);
 112 }
 113 EXPORT_SYMBOL_GPL(timerqueue_iterate_next);