/* kernel/rwsem.c: R/W semaphores, public implementation * * Written by David Howells (dhowells@redhat.com). * Derived from asm-i386/semaphore.h */ #include <linux/types.h>#include <linux/kernel.h>#include <linux/sched.h>#include <linux/module.h>#include <linux/rwsem.h> #include <asm/system.h>#include <linux/atomic.h> /* * lock for reading */void __sched down_read(struct rw_semaphore *sem){	might_sleep();	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); 	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);} EXPORT_SYMBOL(down_read); /* * trylock for reading -- returns 1 if successful, 0 if contention */int down_read_trylock(struct rw_semaphore *sem){	int ret = __down_read_trylock(sem); 	if (ret == 1)		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);	return ret;} EXPORT_SYMBOL(down_read_trylock); /* * lock for writing */void __sched down_write(struct rw_semaphore *sem){	might_sleep();	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); 	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);} EXPORT_SYMBOL(down_write); /* * trylock for writing -- returns 1 if successful, 0 if contention */int down_write_trylock(struct rw_semaphore *sem){	int ret = __down_write_trylock(sem); 	if (ret == 1)		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);	return ret;} EXPORT_SYMBOL(down_write_trylock); /* * release a read lock */void up_read(struct rw_semaphore *sem){	rwsem_release(&sem->dep_map, 1, _RET_IP_); 	__up_read(sem);} EXPORT_SYMBOL(up_read); /* * release a write lock */void up_write(struct rw_semaphore *sem){	rwsem_release(&sem->dep_map, 1, _RET_IP_); 	__up_write(sem);} EXPORT_SYMBOL(up_write); /* * downgrade write lock to read lock */void downgrade_write(struct rw_semaphore *sem){	/*	 * lockdep: a downgraded write will live on as a write	 * dependency.	 */	__downgrade_write(sem);} EXPORT_SYMBOL(downgrade_write); #ifdef CONFIG_DEBUG_LOCK_ALLOC void down_read_nested(struct rw_semaphore *sem, int subclass){	might_sleep();	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_); 	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);} EXPORT_SYMBOL(down_read_nested); void down_write_nested(struct rw_semaphore *sem, int subclass){	might_sleep();	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_); 	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);} EXPORT_SYMBOL(down_write_nested); #endif