[deliverable/linux.git] / include / linux / rwsem.h

/* rwsem.h: R/W semaphores, public interface
 *
 * Written by David Howells (dhowells@redhat.com).
 * Derived from asm-i386/semaphore.h
 */

#ifndef _LINUX_RWSEM_H
#define _LINUX_RWSEM_H

#include <linux/linkage.h>

#ifdef __KERNEL__

#include <linux/types.h>
#include <linux/kernel.h>
#include <asm/system.h>
#include <asm/atomic.h>

struct rw_semaphore;

#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
#include <linux/rwsem-spinlock.h> /* use a generic implementation */
#else
#include <asm/rwsem.h> /* use an arch-specific implementation */
#endif

/*
 * lock for reading
 */
extern void down_read(struct rw_semaphore *sem);

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
extern int down_read_trylock(struct rw_semaphore *sem);

/*
 * lock for writing
 */
extern void down_write(struct rw_semaphore *sem);

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
extern int down_write_trylock(struct rw_semaphore *sem);

/*
 * release a read lock
 */
extern void up_read(struct rw_semaphore *sem);

/*
 * release a write lock
 */
extern void up_write(struct rw_semaphore *sem);

/*
 * downgrade write lock to read lock
 */
extern void downgrade_write(struct rw_semaphore *sem);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
 * nested locking. NOTE: rwsems are not allowed to recurse
 * (which occurs if the same task tries to acquire the same
 * lock instance multiple times), but multiple locks of the
 * same lock class might be taken, if the order of the locks
 * is always the same. This ordering rule can be expressed
 * to lockdep via the _nested() APIs, but enumerating the
 * subclasses that are used. (If the nesting relationship is
 * static then another method for expressing nested locking is
 * the explicit definition of lock class keys and the use of
 * lockdep_set_class() at lock initialization time.
 * See Documentation/lockdep-design.txt for more details.)
 */
extern void down_read_nested(struct rw_semaphore *sem, int subclass);
extern void down_write_nested(struct rw_semaphore *sem, int subclass);
/*
 * Take/release a lock when not the owner will release it.
 *
 * [ This API should be avoided as much as possible - the
 *   proper abstraction for this case is completions. ]
 */
extern void down_read_non_owner(struct rw_semaphore *sem);
extern void up_read_non_owner(struct rw_semaphore *sem);
#else
# define down_read_nested(sem, subclass)		down_read(sem)
# define down_write_nested(sem, subclass)	down_write(sem)
# define down_read_non_owner(sem)		down_read(sem)
# define up_read_non_owner(sem)			up_read(sem)
#endif

#endif /* __KERNEL__ */
#endif /* _LINUX_RWSEM_H */
Commit	Line	Data
1da177e4 LT	1	/* rwsem.h: R/W semaphores, public interface
	2	*
	3	* Written by David Howells (dhowells@redhat.com).
	4	* Derived from asm-i386/semaphore.h
	5	*/
	6
	7	#ifndef _LINUX_RWSEM_H
	8	#define _LINUX_RWSEM_H
	9
	10	#include <linux/linkage.h>
	11
1da177e4 LT	12	#ifdef __KERNEL__
1da177e4 LT	13
1da177e4 LT	14	#include <linux/types.h>
	15	#include <linux/kernel.h>
	16	#include <asm/system.h>
	17	#include <asm/atomic.h>
	18
	19	struct rw_semaphore;
	20
	21	#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
	22	#include <linux/rwsem-spinlock.h> /* use a generic implementation */
	23	#else
	24	#include <asm/rwsem.h> /* use an arch-specific implementation */
	25	#endif
	26
1da177e4 LT	27	/*
	28	* lock for reading
	29	*/
4ea2176d	30	extern void down_read(struct rw_semaphore *sem);
1da177e4 LT	31
	32	/*
	33	* trylock for reading -- returns 1 if successful, 0 if contention
	34	*/
4ea2176d	35	extern int down_read_trylock(struct rw_semaphore *sem);
1da177e4 LT	36
	37	/*
	38	* lock for writing
	39	*/
4ea2176d	40	extern void down_write(struct rw_semaphore *sem);
1da177e4 LT	41
	42	/*
	43	* trylock for writing -- returns 1 if successful, 0 if contention
	44	*/
4ea2176d	45	extern int down_write_trylock(struct rw_semaphore *sem);
1da177e4 LT	46
	47	/*
	48	* release a read lock
	49	*/
4ea2176d	50	extern void up_read(struct rw_semaphore *sem);
1da177e4 LT	51
	52	/*
	53	* release a write lock
	54	*/
4ea2176d	55	extern void up_write(struct rw_semaphore *sem);
1da177e4 LT	56
	57	/*
	58	* downgrade write lock to read lock
	59	*/
4ea2176d IM	60	extern void downgrade_write(struct rw_semaphore *sem);
	61
	62	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	63	/*
5fca80e8 IM	64	* nested locking. NOTE: rwsems are not allowed to recurse
	65	* (which occurs if the same task tries to acquire the same
	66	* lock instance multiple times), but multiple locks of the
	67	* same lock class might be taken, if the order of the locks
	68	* is always the same. This ordering rule can be expressed
	69	* to lockdep via the _nested() APIs, but enumerating the
	70	* subclasses that are used. (If the nesting relationship is
	71	* static then another method for expressing nested locking is
	72	* the explicit definition of lock class keys and the use of
	73	* lockdep_set_class() at lock initialization time.
	74	* See Documentation/lockdep-design.txt for more details.)
4ea2176d IM	75	*/
	76	extern void down_read_nested(struct rw_semaphore *sem, int subclass);
	77	extern void down_write_nested(struct rw_semaphore *sem, int subclass);
	78	/*
5fca80e8 IM	79	* Take/release a lock when not the owner will release it.
	80	*
	81	* [ This API should be avoided as much as possible - the
	82	* proper abstraction for this case is completions. ]
4ea2176d IM	83	*/
	84	extern void down_read_non_owner(struct rw_semaphore *sem);
	85	extern void up_read_non_owner(struct rw_semaphore *sem);
	86	#else
	87	# define down_read_nested(sem, subclass) down_read(sem)
	88	# define down_write_nested(sem, subclass) down_write(sem)
	89	# define down_read_non_owner(sem) down_read(sem)
	90	# define up_read_non_owner(sem) up_read(sem)
	91	#endif
1da177e4 LT	92
	93	#endif /* __KERNEL__ */
	94	#endif /* _LINUX_RWSEM_H */