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

/* rwsem.h: R/W semaphores, public interface
 *
 * Written by David Howells ([email protected]).
 * 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 <linux/list.h>
#include <linux/spinlock.h>

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

struct rw_semaphore;

#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
#include <linux/rwsem-spinlock.h> /* use a generic implementation */
#else
/* All arch specific implementations share the same struct */
struct rw_semaphore {
	long			count;
	raw_spinlock_t		wait_lock;
	struct list_head	wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map	dep_map;
#endif
};

extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);

/* Include the arch specific part */
#include <asm/rwsem.h>

/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
	return sem->count != 0;
}

#endif

/* Common initializer macros and functions */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif

#define __RWSEM_INITIALIZER(name)			\
	{ RWSEM_UNLOCKED_VALUE,				\
	  __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
	  LIST_HEAD_INIT((name).wait_list)		\
	  __RWSEM_DEP_MAP_INIT(name) }

#define DECLARE_RWSEM(name) \
	struct rw_semaphore name = __RWSEM_INITIALIZER(name)

extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
			 struct lock_class_key *key);

#define init_rwsem(sem)						\
do {								\
	static struct lock_class_key __key;			\
								\
	__init_rwsem((sem), #sem, &__key);			\
} while (0)

/*
 * 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);
#else
# define down_read_nested(sem, subclass)		down_read(sem)
# define down_write_nested(sem, subclass)	down_write(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 ([email protected]).
	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>
1da177e4 LT	13	#include <linux/kernel.h>
c16a87ce TG	14	#include <linux/list.h>
	15	#include <linux/spinlock.h>
	16
1da177e4	17	#include <asm/system.h>
60063497	18	#include <linux/atomic.h>
1da177e4 LT	19
	20	struct rw_semaphore;
	21
	22	#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
	23	#include <linux/rwsem-spinlock.h> /* use a generic implementation */
	24	#else
1c8ed640 TG	25	/* All arch specific implementations share the same struct */
	26	struct rw_semaphore {
	27	long count;
ddb6c9b5	28	raw_spinlock_t wait_lock;
1c8ed640 TG	29	struct list_head wait_list;
	30	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	31	struct lockdep_map dep_map;
	32	#endif
	33	};
	34
d1233754 TG	35	extern struct rw_semaphore rwsem_down_read_failed(struct rw_semaphore sem);
	36	extern struct rw_semaphore rwsem_down_write_failed(struct rw_semaphore sem);
	37	extern struct rw_semaphore rwsem_wake(struct rw_semaphore );
	38	extern struct rw_semaphore rwsem_downgrade_wake(struct rw_semaphore sem);
aac72277	39
1c8ed640 TG	40	/* Include the arch specific part */
1c8ed640 TG	41	#include <asm/rwsem.h>
41e5887f TG	42
	43	/* In all implementations count != 0 means locked */
	44	static inline int rwsem_is_locked(struct rw_semaphore *sem)
	45	{
	46	return sem->count != 0;
	47	}
	48
1da177e4 LT	49	#endif
1da177e4 LT	50
12249b34 TG	51	/* Common initializer macros and functions */
	52
	53	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	54	# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
	55	#else
	56	# define __RWSEM_DEP_MAP_INIT(lockname)
	57	#endif
	58
ddb6c9b5 TG	59	#define __RWSEM_INITIALIZER(name) \
	60	{ RWSEM_UNLOCKED_VALUE, \
	61	__RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
	62	LIST_HEAD_INIT((name).wait_list) \
	63	__RWSEM_DEP_MAP_INIT(name) }
12249b34 TG	64
	65	#define DECLARE_RWSEM(name) \
	66	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
	67
	68	extern void __init_rwsem(struct rw_semaphore sem, const char name,
	69	struct lock_class_key *key);
	70
	71	#define init_rwsem(sem) \
	72	do { \
	73	static struct lock_class_key __key; \
	74	\
	75	__init_rwsem((sem), #sem, &__key); \
	76	} while (0)
	77
1da177e4 LT	78	/*
	79	* lock for reading
	80	*/
4ea2176d	81	extern void down_read(struct rw_semaphore *sem);
1da177e4 LT	82
	83	/*
	84	* trylock for reading -- returns 1 if successful, 0 if contention
	85	*/
4ea2176d	86	extern int down_read_trylock(struct rw_semaphore *sem);
1da177e4 LT	87
	88	/*
	89	* lock for writing
	90	*/
4ea2176d	91	extern void down_write(struct rw_semaphore *sem);
1da177e4 LT	92
	93	/*
	94	* trylock for writing -- returns 1 if successful, 0 if contention
	95	*/
4ea2176d	96	extern int down_write_trylock(struct rw_semaphore *sem);
1da177e4 LT	97
	98	/*
	99	* release a read lock
	100	*/
4ea2176d	101	extern void up_read(struct rw_semaphore *sem);
1da177e4 LT	102
	103	/*
	104	* release a write lock
	105	*/
4ea2176d	106	extern void up_write(struct rw_semaphore *sem);
1da177e4 LT	107
	108	/*
	109	* downgrade write lock to read lock
	110	*/
4ea2176d IM	111	extern void downgrade_write(struct rw_semaphore *sem);
	112
	113	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	114	/*
5fca80e8 IM	115	* nested locking. NOTE: rwsems are not allowed to recurse
	116	* (which occurs if the same task tries to acquire the same
	117	* lock instance multiple times), but multiple locks of the
	118	* same lock class might be taken, if the order of the locks
	119	* is always the same. This ordering rule can be expressed
	120	* to lockdep via the _nested() APIs, but enumerating the
	121	* subclasses that are used. (If the nesting relationship is
	122	* static then another method for expressing nested locking is
	123	* the explicit definition of lock class keys and the use of
	124	* lockdep_set_class() at lock initialization time.
	125	* See Documentation/lockdep-design.txt for more details.)
4ea2176d IM	126	*/
	127	extern void down_read_nested(struct rw_semaphore *sem, int subclass);
	128	extern void down_write_nested(struct rw_semaphore *sem, int subclass);
4ea2176d IM	129	#else
	130	# define down_read_nested(sem, subclass) down_read(sem)
	131	# define down_write_nested(sem, subclass) down_write(sem)
4ea2176d	132	#endif
1da177e4	133
1da177e4	134	#endif /* _LINUX_RWSEM_H */