/* kernel/rwsem.c: R/W semaphores, public implementation
   *
   * Written by David Howells (dhowells@redhat.com).
   * Derived from asm-i386/semaphore.h
   */
  
  #include <linux/types.h>
  #include <linux/kernel.h>

  #include <linux/sched.h>

  #include <linux/export.h>

  #include <linux/rwsem.h>
  
  #include <asm/system.h>

  #include <linux/atomic.h>

  
  /*
   * lock for reading
   */

  void __sched down_read(struct rw_semaphore *sem)

  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);

  }
  
  EXPORT_SYMBOL(down_read);
  
  /*
   * trylock for reading -- returns 1 if successful, 0 if contention
   */
  int down_read_trylock(struct rw_semaphore *sem)
  {
  	int ret = __down_read_trylock(sem);
  
  	if (ret == 1)
  		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  	return ret;
  }
  
  EXPORT_SYMBOL(down_read_trylock);
  
  /*
   * lock for writing
   */

  void __sched down_write(struct rw_semaphore *sem)

  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);

  }
  
  EXPORT_SYMBOL(down_write);
  
  /*
   * trylock for writing -- returns 1 if successful, 0 if contention
   */
  int down_write_trylock(struct rw_semaphore *sem)
  {
  	int ret = __down_write_trylock(sem);
  
  	if (ret == 1)

  		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);

  	return ret;
  }
  
  EXPORT_SYMBOL(down_write_trylock);
  
  /*
   * release a read lock
   */
  void up_read(struct rw_semaphore *sem)
  {
  	rwsem_release(&sem->dep_map, 1, _RET_IP_);
  
  	__up_read(sem);
  }
  
  EXPORT_SYMBOL(up_read);
  
  /*
   * release a write lock
   */
  void up_write(struct rw_semaphore *sem)
  {
  	rwsem_release(&sem->dep_map, 1, _RET_IP_);
  
  	__up_write(sem);
  }
  
  EXPORT_SYMBOL(up_write);
  
  /*
   * downgrade write lock to read lock
   */
  void downgrade_write(struct rw_semaphore *sem)
  {
  	/*
  	 * lockdep: a downgraded write will live on as a write
  	 * dependency.
  	 */
  	__downgrade_write(sem);
  }
  
  EXPORT_SYMBOL(downgrade_write);

  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  
  void down_read_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);

  }
  
  EXPORT_SYMBOL(down_read_nested);

  void down_write_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);

  }
  
  EXPORT_SYMBOL(down_write_nested);

  #endif