rwsem.h

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/*
 * rwsem.h: R/W semaphores implemented using CAS
 *
 * Written by David S. Miller ([email protected]), 2001.
 * Derived from asm-i386/rwsem.h
 */
#ifndef _SPARC64_RWSEM_H
#define _SPARC64_RWSEM_H

#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__

#define RWSEM_UNLOCKED_VALUE        0x00000000L
#define RWSEM_ACTIVE_BIAS       0x00000001L
#define RWSEM_ACTIVE_MASK       0xffffffffL
#define RWSEM_WAITING_BIAS      (-RWSEM_ACTIVE_MASK-1)
#define RWSEM_ACTIVE_READ_BIAS      RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS     (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
    if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
        rwsem_down_read_failed(sem);
}

static inline int __down_read_trylock(struct rw_semaphore *sem)
{
    long tmp;

    while ((tmp = sem->count) >= 0L) {
        if (tmp == cmpxchg(&sem->count, tmp,
                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
            return 1;
        }
    }
    return 0;
}

/*
 * lock for writing
 */
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
    long tmp;

    tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
                  (atomic64_t *)(&sem->count));
    if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
        rwsem_down_write_failed(sem);
}

static inline void __down_write(struct rw_semaphore *sem)
{
    __down_write_nested(sem, 0);
}

static inline int __down_write_trylock(struct rw_semaphore *sem)
{
    long tmp;

    tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
              RWSEM_ACTIVE_WRITE_BIAS);
    return tmp == RWSEM_UNLOCKED_VALUE;
}

/*
 * unlock after reading
 */
static inline void __up_read(struct rw_semaphore *sem)
{
    long tmp;

    tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
    if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
        rwsem_wake(sem);
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
    if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
                     (atomic64_t *)(&sem->count)) < 0L))
        rwsem_wake(sem);
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
{
    atomic64_add(delta, (atomic64_t *)(&sem->count));
}

/*
 * downgrade write lock to read lock
 */
static inline void __downgrade_write(struct rw_semaphore *sem)
{
    long tmp;

    tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
    if (tmp < 0L)
        rwsem_downgrade_wake(sem);
}

/*
 * implement exchange and add functionality
 */
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
    return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
}

#endif /* __KERNEL__ */

#endif /* _SPARC64_RWSEM_H */