1 /* rwsem.h: R/W semaphores, public interface 2 * 3 * Written by David Howells ([email protected]). 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 <linux/list.h> 15 #include <linux/spinlock.h> 16 17 #include <asm/system.h> 18 #include <linux/atomic.h> 19 20 struct rw_semaphore; 21 22 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK 23 #include <linux/rwsem-spinlock.h> /* use a generic implementation */ 24 #else 25 /* All arch specific implementations share the same struct */ 26 struct rw_semaphore { 27 long count; 28 raw_spinlock_t wait_lock; 29 struct list_head wait_list; 30 #ifdef CONFIG_DEBUG_LOCK_ALLOC 31 struct lockdep_map dep_map; 32 #endif 33 }; 34 35 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); 36 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); 37 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); 38 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); 39 40 /* Include the arch specific part */ 41 #include <asm/rwsem.h> 42 43 /* In all implementations count != 0 means locked */ 44 static inline int rwsem_is_locked(struct rw_semaphore *sem) 45 { 46 return sem->count != 0; 47 } 48 49 #endif 50 51 /* Common initializer macros and functions */ 52 53 #ifdef CONFIG_DEBUG_LOCK_ALLOC 54 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } 55 #else 56 # define __RWSEM_DEP_MAP_INIT(lockname) 57 #endif 58 59 #define __RWSEM_INITIALIZER(name) \ 60 { RWSEM_UNLOCKED_VALUE, \ 61 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \ 62 LIST_HEAD_INIT((name).wait_list) \ 63 __RWSEM_DEP_MAP_INIT(name) } 64 65 #define DECLARE_RWSEM(name) \ 66 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 67 68 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 69 struct lock_class_key *key); 70 71 #define init_rwsem(sem) \ 72 do { \ 73 static struct lock_class_key __key; \ 74 \ 75 __init_rwsem((sem), #sem, &__key); \ 76 } while (0) 77 78 /* 79 * lock for reading 80 */ 81 extern void down_read(struct rw_semaphore *sem); 82 83 /* 84 * trylock for reading -- returns 1 if successful, 0 if contention 85 */ 86 extern int down_read_trylock(struct rw_semaphore *sem); 87 88 /* 89 * lock for writing 90 */ 91 extern void down_write(struct rw_semaphore *sem); 92 93 /* 94 * trylock for writing -- returns 1 if successful, 0 if contention 95 */ 96 extern int down_write_trylock(struct rw_semaphore *sem); 97 98 /* 99 * release a read lock 100 */ 101 extern void up_read(struct rw_semaphore *sem); 102 103 /* 104 * release a write lock 105 */ 106 extern void up_write(struct rw_semaphore *sem); 107 108 /* 109 * downgrade write lock to read lock 110 */ 111 extern void downgrade_write(struct rw_semaphore *sem); 112 113 #ifdef CONFIG_DEBUG_LOCK_ALLOC 114 /* 115 * nested locking. NOTE: rwsems are not allowed to recurse 116 * (which occurs if the same task tries to acquire the same 117 * lock instance multiple times), but multiple locks of the 118 * same lock class might be taken, if the order of the locks 119 * is always the same. This ordering rule can be expressed 120 * to lockdep via the _nested() APIs, but enumerating the 121 * subclasses that are used. (If the nesting relationship is 122 * static then another method for expressing nested locking is 123 * the explicit definition of lock class keys and the use of 124 * lockdep_set_class() at lock initialization time. 125 * See Documentation/lockdep-design.txt for more details.) 126 */ 127 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 128 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 129 #else 130 # define down_read_nested(sem, subclass) down_read(sem) 131 # define down_write_nested(sem, subclass) down_write(sem) 132 #endif 133 134 #endif /* _LINUX_RWSEM_H */ 135