| /* rwsem.h: R/W semaphores, public interface |
| * |
| * Written by David Howells (dhowells@redhat.com). |
| * Derived from asm-i386/semaphore.h |
| */ |
| |
| #ifndef _LINUX_RWSEM_H |
| #define _LINUX_RWSEM_H |
| |
| #include <linux/linkage.h> |
| |
| #include <linux/types.h> |
| #include <linux/kernel.h> |
| #include <linux/list.h> |
| #include <linux/spinlock.h> |
| |
| #include <asm/system.h> |
| #include <asm/atomic.h> |
| |
| struct rw_semaphore; |
| |
| #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK |
| #include <linux/rwsem-spinlock.h> /* use a generic implementation */ |
| #else |
| /* All arch specific implementations share the same struct */ |
| struct rw_semaphore { |
| long count; |
| spinlock_t wait_lock; |
| struct list_head wait_list; |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| struct lockdep_map dep_map; |
| #endif |
| }; |
| |
| extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); |
| extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); |
| extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); |
| extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); |
| |
| /* Include the arch specific part */ |
| #include <asm/rwsem.h> |
| |
| /* In all implementations count != 0 means locked */ |
| static inline int rwsem_is_locked(struct rw_semaphore *sem) |
| { |
| return sem->count != 0; |
| } |
| |
| #endif |
| |
| /* Common initializer macros and functions */ |
| |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } |
| #else |
| # define __RWSEM_DEP_MAP_INIT(lockname) |
| #endif |
| |
| #define __RWSEM_INITIALIZER(name) \ |
| { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED(name.wait_lock), \ |
| LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) } |
| |
| #define DECLARE_RWSEM(name) \ |
| struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
| |
| extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
| struct lock_class_key *key); |
| |
| #define init_rwsem(sem) \ |
| do { \ |
| static struct lock_class_key __key; \ |
| \ |
| __init_rwsem((sem), #sem, &__key); \ |
| } while (0) |
| |
| /* |
| * lock for reading |
| */ |
| extern void down_read(struct rw_semaphore *sem); |
| |
| /* |
| * trylock for reading -- returns 1 if successful, 0 if contention |
| */ |
| extern int down_read_trylock(struct rw_semaphore *sem); |
| |
| /* |
| * lock for writing |
| */ |
| extern void down_write(struct rw_semaphore *sem); |
| |
| /* |
| * trylock for writing -- returns 1 if successful, 0 if contention |
| */ |
| extern int down_write_trylock(struct rw_semaphore *sem); |
| |
| /* |
| * release a read lock |
| */ |
| extern void up_read(struct rw_semaphore *sem); |
| |
| /* |
| * release a write lock |
| */ |
| extern void up_write(struct rw_semaphore *sem); |
| |
| /* |
| * downgrade write lock to read lock |
| */ |
| extern void downgrade_write(struct rw_semaphore *sem); |
| |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| /* |
| * nested locking. NOTE: rwsems are not allowed to recurse |
| * (which occurs if the same task tries to acquire the same |
| * lock instance multiple times), but multiple locks of the |
| * same lock class might be taken, if the order of the locks |
| * is always the same. This ordering rule can be expressed |
| * to lockdep via the _nested() APIs, but enumerating the |
| * subclasses that are used. (If the nesting relationship is |
| * static then another method for expressing nested locking is |
| * the explicit definition of lock class keys and the use of |
| * lockdep_set_class() at lock initialization time. |
| * See Documentation/lockdep-design.txt for more details.) |
| */ |
| extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
| extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
| #else |
| # define down_read_nested(sem, subclass) down_read(sem) |
| # define down_write_nested(sem, subclass) down_write(sem) |
| #endif |
| |
| #endif /* _LINUX_RWSEM_H */ |