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include/asm-generic/rwsem.h
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#ifndef _ASM_GENERIC_RWSEM_H #define _ASM_GENERIC_RWSEM_H |
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#ifndef _LINUX_RWSEM_H #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead." #endif #ifdef __KERNEL__ /* |
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* R/W semaphores originally for PPC using the stuff in lib/rwsem.c. |
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* Adapted largely from include/asm-i386/rwsem.h * by Paul Mackerras <paulus@samba.org>. */ /* * the semaphore definition */ |
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#ifdef CONFIG_64BIT |
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# define RWSEM_ACTIVE_MASK 0xffffffffL #else # define RWSEM_ACTIVE_MASK 0x0000ffffL #endif #define RWSEM_UNLOCKED_VALUE 0x00000000L #define RWSEM_ACTIVE_BIAS 0x00000001L #define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1) #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS) /* * lock for reading */ static inline void __down_read(struct rw_semaphore *sem) { if (unlikely(atomic_long_inc_return((atomic_long_t *)&sem->count) <= 0)) rwsem_down_read_failed(sem); } static inline int __down_read_trylock(struct rw_semaphore *sem) { long tmp; while ((tmp = sem->count) >= 0) { if (tmp == cmpxchg(&sem->count, tmp, tmp + RWSEM_ACTIVE_READ_BIAS)) { return 1; } } return 0; } /* * lock for writing */ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass) { long tmp; tmp = atomic_long_add_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_long_t *)&sem->count); if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS)) rwsem_down_write_failed(sem); } static inline void __down_write(struct rw_semaphore *sem) { __down_write_nested(sem, 0); } static inline int __down_write_trylock(struct rw_semaphore *sem) { long tmp; tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS); return tmp == RWSEM_UNLOCKED_VALUE; } /* * unlock after reading */ static inline void __up_read(struct rw_semaphore *sem) { long tmp; tmp = atomic_long_dec_return((atomic_long_t *)&sem->count); if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)) rwsem_wake(sem); } /* * unlock after writing */ static inline void __up_write(struct rw_semaphore *sem) { if (unlikely(atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_long_t *)&sem->count) < 0)) rwsem_wake(sem); } /* * implement atomic add functionality */ static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem) { atomic_long_add(delta, (atomic_long_t *)&sem->count); } /* * downgrade write lock to read lock */ static inline void __downgrade_write(struct rw_semaphore *sem) { long tmp; tmp = atomic_long_add_return(-RWSEM_WAITING_BIAS, (atomic_long_t *)&sem->count); if (tmp < 0) rwsem_downgrade_wake(sem); } /* * implement exchange and add functionality */ static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem) { return atomic_long_add_return(delta, (atomic_long_t *)&sem->count); } #endif /* __KERNEL__ */ |
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#endif /* _ASM_GENERIC_RWSEM_H */ |