#ifndef __LINUX_OSQ_LOCK_H
  #define __LINUX_OSQ_LOCK_H
  
  /*
   * An MCS like lock especially tailored for optimistic spinning for sleeping
   * lock implementations (mutex, rwsem, etc).
   */

  struct optimistic_spin_node {
  	struct optimistic_spin_node *next, *prev;
  	int locked; /* 1 if lock acquired */
  	int cpu; /* encoded CPU # + 1 value */
  };

  
  struct optimistic_spin_queue {
  	/*
  	 * Stores an encoded value of the CPU # of the tail node in the queue.
  	 * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
  	 */
  	atomic_t tail;
  };

  #define OSQ_UNLOCKED_VAL (0)

  /* Init macro and function. */
  #define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
  
  static inline void osq_lock_init(struct optimistic_spin_queue *lock)
  {
  	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
  }

  extern bool osq_lock(struct optimistic_spin_queue *lock);
  extern void osq_unlock(struct optimistic_spin_queue *lock);

  static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
  {
  	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
  }

  #endif