xref: /openbmc/linux/lib/timerqueue.c (revision a2818ee4)
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);
114