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