[net-next-2.6.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>

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