1 /* rwsem-spinlock.h: fallback C implementation 2 * 3 * Copyright (c) 2001 David Howells (dhowells@redhat.com). 4 * - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de> 5 * - Derived also from comments by Linus 6 */ 7 8 #ifndef _LINUX_RWSEM_SPINLOCK_H 9 #define _LINUX_RWSEM_SPINLOCK_H 10 11 #ifndef _LINUX_RWSEM_H 12 #error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead" 13 #endif 14 15 #ifdef __KERNEL__ 16 /* 17 * the rw-semaphore definition 18 * - if activity is 0 then there are no active readers or writers 19 * - if activity is +ve then that is the number of active readers 20 * - if activity is -1 then there is one active writer 21 * - if wait_list is not empty, then there are processes waiting for the semaphore 22 */ 23 struct rw_semaphore { 24 __s32 activity; 25 raw_spinlock_t wait_lock; 26 struct list_head wait_list; 27 #ifdef CONFIG_DEBUG_LOCK_ALLOC 28 struct lockdep_map dep_map; 29 #endif 30 }; 31 32 #define RWSEM_UNLOCKED_VALUE 0x00000000 33 34 extern void __down_read(struct rw_semaphore *sem); 35 extern int __down_read_trylock(struct rw_semaphore *sem); 36 extern void __down_write(struct rw_semaphore *sem); 37 extern void __down_write_nested(struct rw_semaphore *sem, int subclass); 38 extern int __down_write_trylock(struct rw_semaphore *sem); 39 extern void __up_read(struct rw_semaphore *sem); 40 extern void __up_write(struct rw_semaphore *sem); 41 extern void __downgrade_write(struct rw_semaphore *sem); 42 extern int rwsem_is_locked(struct rw_semaphore *sem); 43 44 #endif /* __KERNEL__ */ 45 #endif /* _LINUX_RWSEM_SPINLOCK_H */ 46