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include/linux/rwsem.h
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/* 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> |
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#include <linux/types.h> #include <linux/kernel.h> |
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#include <linux/list.h> #include <linux/spinlock.h> |
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#include <asm/system.h> |
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#include <linux/atomic.h> |
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struct rw_semaphore; #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK #include <linux/rwsem-spinlock.h> /* use a generic implementation */ #else |
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/* All arch specific implementations share the same struct */ struct rw_semaphore { long count; |
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raw_spinlock_t wait_lock; |
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struct list_head wait_list; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif }; |
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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); |
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/* Include the arch specific part */ #include <asm/rwsem.h> |
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/* In all implementations count != 0 means locked */ static inline int rwsem_is_locked(struct rw_semaphore *sem) { return sem->count != 0; } |
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#endif |
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/* 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 |
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#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) } |
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#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) |
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/* * lock for reading */ |
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extern void down_read(struct rw_semaphore *sem); |
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/* * trylock for reading -- returns 1 if successful, 0 if contention */ |
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extern int down_read_trylock(struct rw_semaphore *sem); |
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/* * lock for writing */ |
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extern void down_write(struct rw_semaphore *sem); |
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/* * trylock for writing -- returns 1 if successful, 0 if contention */ |
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extern int down_write_trylock(struct rw_semaphore *sem); |
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/* * release a read lock */ |
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extern void up_read(struct rw_semaphore *sem); |
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/* * release a write lock */ |
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extern void up_write(struct rw_semaphore *sem); |
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/* * downgrade write lock to read lock */ |
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extern void downgrade_write(struct rw_semaphore *sem); #ifdef CONFIG_DEBUG_LOCK_ALLOC /* |
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* 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.) |
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*/ extern void down_read_nested(struct rw_semaphore *sem, int subclass); extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
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#else # define down_read_nested(sem, subclass) down_read(sem) # define down_write_nested(sem, subclass) down_write(sem) |
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#endif |
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#endif /* _LINUX_RWSEM_H */ |