FreeBSD/Linux Kernel Cross Reference
sys/kernel/rwsem.c

     /* 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/export.h>
    #include <linux/rwsem.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_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
   {
           might_sleep();
           rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
   
           LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
   }
   
   EXPORT_SYMBOL(_down_write_nest_lock);
   
   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
   
   

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