// SPDX-License-Identifier: GPL-2.0-or-later
  /*
   *  Generic Timer-queue
   *
   *  Manages a simple queue of timers, ordered by expiration time.
   *  Uses rbtrees for quick list adds and expiration.
   *
   *  NOTE: All of the following functions need to be serialized
   *  to avoid races. No locking is done by this library code.
   */
  
  #include <linux/bug.h>
  #include <linux/timerqueue.h>
  #include <linux/rbtree.h>
  #include <linux/export.h>
  
  /**
   * timerqueue_add - Adds timer to timerqueue.
   *
   * @head: head of timerqueue
   * @node: timer node to be added
   *
   * Adds the timer node to the timerqueue, sorted by the node's expires
   * value. Returns true if the newly added timer is the first expiring timer in
   * the queue.
   */
  bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
  {
  	struct rb_node **p = &head->rb_root.rb_root.rb_node;
  	struct rb_node *parent = NULL;
  	struct timerqueue_node *ptr;
  	bool leftmost = true;
  
  	/* Make sure we don't add nodes that are already added */
  	WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
  
  	while (*p) {
  		parent = *p;
  		ptr = rb_entry(parent, struct timerqueue_node, node);
  		if (node->expires < ptr->expires) {
  			p = &(*p)->rb_left;
  		} else {
  			p = &(*p)->rb_right;
  			leftmost = false;
  		}
  	}
  	rb_link_node(&node->node, parent, p);
  	rb_insert_color_cached(&node->node, &head->rb_root, leftmost);
  
  	return leftmost;
  }
  EXPORT_SYMBOL_GPL(timerqueue_add);
  
  /**
   * timerqueue_del - Removes a timer from the timerqueue.
   *
   * @head: head of timerqueue
   * @node: timer node to be removed
   *
   * Removes the timer node from the timerqueue. Returns true if the queue is
   * not empty after the remove.
   */
  bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
  {
  	WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
  
  	rb_erase_cached(&node->node, &head->rb_root);
  	RB_CLEAR_NODE(&node->node);
  
  	return !RB_EMPTY_ROOT(&head->rb_root.rb_root);
  }
  EXPORT_SYMBOL_GPL(timerqueue_del);
  
  /**
   * timerqueue_iterate_next - Returns the timer after the provided timer
   *
   * @node: Pointer to a timer.
   *
   * Provides the timer that is after the given node. This is used, when
   * necessary, to iterate through the list of timers in a timer list
   * without modifying the list.
   */
  struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
  {
  	struct rb_node *next;
  
  	if (!node)
  		return NULL;
  	next = rb_next(&node->node);
  	if (!next)
  		return NULL;
  	return container_of(next, struct timerqueue_node, node);
  }
  EXPORT_SYMBOL_GPL(timerqueue_iterate_next);