1 /* rwsem.h: R/W semaphores, public interface 2 * 3 * Written by David Howells (dhowells (at) 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 12 #ifdef __KERNEL__ 13 14 #include <linux/types.h> 15 #include <linux/kernel.h> 16 #include <asm/system.h> 17 #include <asm/atomic.h> 18 19 struct rw_semaphore; 20 21 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK 22 #include <linux/rwsem-spinlock.h> /* use a generic implementation */ 23 #else 24 #include <asm/rwsem.h> /* use an arch-specific implementation */ 25 #endif 26 27 /* 28 * lock for reading 29 */ 30 extern void down_read(struct rw_semaphore *sem); 31 32 /* 33 * trylock for reading -- returns 1 if successful, 0 if contention 34 */ 35 extern int down_read_trylock(struct rw_semaphore *sem); 36 37 /* 38 * lock for writing 39 */ 40 extern void down_write(struct rw_semaphore *sem); 41 42 /* 43 * trylock for writing -- returns 1 if successful, 0 if contention 44 */ 45 extern int down_write_trylock(struct rw_semaphore *sem); 46 47 /* 48 * release a read lock 49 */ 50 extern void up_read(struct rw_semaphore *sem); 51 52 /* 53 * release a write lock 54 */ 55 extern void up_write(struct rw_semaphore *sem); 56 57 /* 58 * downgrade write lock to read lock 59 */ 60 extern void downgrade_write(struct rw_semaphore *sem); 61 62 #ifdef CONFIG_DEBUG_LOCK_ALLOC 63 /* 64 * nested locking. NOTE: rwsems are not allowed to recurse 65 * (which occurs if the same task tries to acquire the same 66 * lock instance multiple times), but multiple locks of the 67 * same lock class might be taken, if the order of the locks 68 * is always the same. This ordering rule can be expressed 69 * to lockdep via the _nested() APIs, but enumerating the 70 * subclasses that are used. (If the nesting relationship is 71 * static then another method for expressing nested locking is 72 * the explicit definition of lock class keys and the use of 73 * lockdep_set_class() at lock initialization time. 74 * See Documentation/lockdep-design.txt for more details.) 75 */ 76 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 77 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 78 /* 79 * Take/release a lock when not the owner will release it. 80 * 81 * [ This API should be avoided as much as possible - the 82 * proper abstraction for this case is completions. ] 83 */ 84 extern void down_read_non_owner(struct rw_semaphore *sem); 85 extern void up_read_non_owner(struct rw_semaphore *sem); 86 #else 87 # define down_read_nested(sem, subclass) down_read(sem) 88 # define down_write_nested(sem, subclass) down_write(sem) 89 # define down_read_non_owner(sem) down_read(sem) 90 # define up_read_non_owner(sem) up_read(sem) 91 #endif 92 93 #endif /* __KERNEL__ */ 94 #endif /* _LINUX_RWSEM_H */ 95
