/*
   * Generic waiting primitives.
   *
   * (C) 2004 William Irwin, Oracle
   */

  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <linux/wait.h>
  #include <linux/hash.h>

  void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *key)

  {
  	spin_lock_init(&q->lock);

  	lockdep_set_class(&q->lock, key);

  	INIT_LIST_HEAD(&q->task_list);
  }

  EXPORT_SYMBOL(__init_waitqueue_head);

  void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	__add_wait_queue(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(add_wait_queue);

  void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	wait->flags |= WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	__add_wait_queue_tail(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(add_wait_queue_exclusive);

  void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&q->lock, flags);
  	__remove_wait_queue(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(remove_wait_queue);
  
  
  /*
   * Note: we use "set_current_state()" _after_ the wait-queue add,
   * because we need a memory barrier there on SMP, so that any
   * wake-function that tests for the wait-queue being active
   * will be guaranteed to see waitqueue addition _or_ subsequent
   * tests in this thread will see the wakeup having taken place.
   *
   * The spin_unlock() itself is semi-permeable and only protects
   * one way (it only protects stuff inside the critical region and
   * stops them from bleeding out - it would still allow subsequent

   * loads to move into the critical region).

   */

  void

  prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
  {
  	unsigned long flags;
  
  	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	if (list_empty(&wait->task_list))
  		__add_wait_queue(q, wait);

  	set_current_state(state);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(prepare_to_wait);

  void

  prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
  {
  	unsigned long flags;
  
  	wait->flags |= WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	if (list_empty(&wait->task_list))
  		__add_wait_queue_tail(q, wait);

  	set_current_state(state);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(prepare_to_wait_exclusive);

  /**

   * finish_wait - clean up after waiting in a queue
   * @q: waitqueue waited on
   * @wait: wait descriptor
   *
   * Sets current thread back to running state and removes
   * the wait descriptor from the given waitqueue if still
   * queued.
   */

  void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	__set_current_state(TASK_RUNNING);
  	/*
  	 * We can check for list emptiness outside the lock
  	 * IFF:
  	 *  - we use the "careful" check that verifies both
  	 *    the next and prev pointers, so that there cannot
  	 *    be any half-pending updates in progress on other
  	 *    CPU's that we haven't seen yet (and that might
  	 *    still change the stack area.
  	 * and
  	 *  - all other users take the lock (ie we can only
  	 *    have _one_ other CPU that looks at or modifies
  	 *    the list).
  	 */
  	if (!list_empty_careful(&wait->task_list)) {
  		spin_lock_irqsave(&q->lock, flags);
  		list_del_init(&wait->task_list);
  		spin_unlock_irqrestore(&q->lock, flags);
  	}
  }
  EXPORT_SYMBOL(finish_wait);

  /**

   * abort_exclusive_wait - abort exclusive waiting in a queue
   * @q: waitqueue waited on
   * @wait: wait descriptor

   * @mode: runstate of the waiter to be woken

   * @key: key to identify a wait bit queue or %NULL
   *
   * Sets current thread back to running state and removes
   * the wait descriptor from the given waitqueue if still
   * queued.
   *
   * Wakes up the next waiter if the caller is concurrently
   * woken up through the queue.
   *
   * This prevents waiter starvation where an exclusive waiter

   * aborts and is woken up concurrently and no one wakes up

   * the next waiter.
   */
  void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
  			unsigned int mode, void *key)
  {
  	unsigned long flags;
  
  	__set_current_state(TASK_RUNNING);
  	spin_lock_irqsave(&q->lock, flags);
  	if (!list_empty(&wait->task_list))
  		list_del_init(&wait->task_list);
  	else if (waitqueue_active(q))

  		__wake_up_locked_key(q, mode, key);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(abort_exclusive_wait);

  int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
  {
  	int ret = default_wake_function(wait, mode, sync, key);
  
  	if (ret)
  		list_del_init(&wait->task_list);
  	return ret;
  }
  EXPORT_SYMBOL(autoremove_wake_function);
  
  int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
  {
  	struct wait_bit_key *key = arg;
  	struct wait_bit_queue *wait_bit
  		= container_of(wait, struct wait_bit_queue, wait);
  
  	if (wait_bit->key.flags != key->flags ||
  			wait_bit->key.bit_nr != key->bit_nr ||
  			test_bit(key->bit_nr, key->flags))
  		return 0;
  	else
  		return autoremove_wake_function(wait, mode, sync, key);
  }
  EXPORT_SYMBOL(wake_bit_function);
  
  /*
   * To allow interruptible waiting and asynchronous (i.e. nonblocking)
   * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
   * permitted return codes. Nonzero return codes halt waiting and return.
   */

  int __sched

  __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
  			int (*action)(void *), unsigned mode)
  {
  	int ret = 0;
  
  	do {
  		prepare_to_wait(wq, &q->wait, mode);
  		if (test_bit(q->key.bit_nr, q->key.flags))
  			ret = (*action)(q->key.flags);
  	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
  	finish_wait(wq, &q->wait);
  	return ret;
  }
  EXPORT_SYMBOL(__wait_on_bit);

  int __sched out_of_line_wait_on_bit(void *word, int bit,

  					int (*action)(void *), unsigned mode)
  {
  	wait_queue_head_t *wq = bit_waitqueue(word, bit);
  	DEFINE_WAIT_BIT(wait, word, bit);
  
  	return __wait_on_bit(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL(out_of_line_wait_on_bit);

  int __sched

  __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
  			int (*action)(void *), unsigned mode)
  {

  	do {

  		int ret;

  		prepare_to_wait_exclusive(wq, &q->wait, mode);

  		if (!test_bit(q->key.bit_nr, q->key.flags))
  			continue;
  		ret = action(q->key.flags);
  		if (!ret)
  			continue;
  		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
  		return ret;

  	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
  	finish_wait(wq, &q->wait);

  	return 0;

  }
  EXPORT_SYMBOL(__wait_on_bit_lock);

  int __sched out_of_line_wait_on_bit_lock(void *word, int bit,

  					int (*action)(void *), unsigned mode)
  {
  	wait_queue_head_t *wq = bit_waitqueue(word, bit);
  	DEFINE_WAIT_BIT(wait, word, bit);
  
  	return __wait_on_bit_lock(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);

  void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)

  {
  	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
  	if (waitqueue_active(wq))

  		__wake_up(wq, TASK_NORMAL, 1, &key);

  }
  EXPORT_SYMBOL(__wake_up_bit);
  
  /**
   * wake_up_bit - wake up a waiter on a bit
   * @word: the word being waited on, a kernel virtual address
   * @bit: the bit of the word being waited on
   *
   * There is a standard hashed waitqueue table for generic use. This
   * is the part of the hashtable's accessor API that wakes up waiters
   * on a bit. For instance, if one were to have waiters on a bitflag,
   * one would call wake_up_bit() after clearing the bit.
   *
   * In order for this to function properly, as it uses waitqueue_active()
   * internally, some kind of memory barrier must be done prior to calling
   * this. Typically, this will be smp_mb__after_clear_bit(), but in some
   * cases where bitflags are manipulated non-atomically under a lock, one
   * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
   * because spin_unlock() does not guarantee a memory barrier.
   */

  void wake_up_bit(void *word, int bit)

  {
  	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
  }
  EXPORT_SYMBOL(wake_up_bit);

  wait_queue_head_t *bit_waitqueue(void *word, int bit)

  {
  	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
  	const struct zone *zone = page_zone(virt_to_page(word));
  	unsigned long val = (unsigned long)word << shift | bit;
  
  	return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
  }
  EXPORT_SYMBOL(bit_waitqueue);