rwsem.h
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#ifndef _ASM_POWERPC_RWSEM_H
#define _ASM_POWERPC_RWSEM_H
#ifdef __KERNEL__
/*
* include/asm-powerpc/rwsem.h: R/W semaphores for PPC using the stuff
* in lib/rwsem.c. Adapted largely from include/asm-i386/rwsem.h
* by Paul Mackerras <paulus@samba.org>.
*/
#include <linux/list.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
#include <asm/system.h>
/*
* the semaphore definition
*/
struct rw_semaphore {
/* XXX this should be able to be an atomic_t -- paulus */
signed int count;
#define RWSEM_UNLOCKED_VALUE 0x00000000
#define RWSEM_ACTIVE_BIAS 0x00000001
#define RWSEM_ACTIVE_MASK 0x0000ffff
#define RWSEM_WAITING_BIAS (-0x00010000)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
spinlock_t wait_lock;
struct list_head wait_list;
};
#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
LIST_HEAD_INIT((name).wait_list) }
#define DECLARE_RWSEM(name) \
struct rw_semaphore name = __RWSEM_INITIALIZER(name)
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 *sem);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
static inline void init_rwsem(struct rw_semaphore *sem)
{
sem->count = RWSEM_UNLOCKED_VALUE;
spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
}
/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))
rwsem_down_read_failed(sem);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
int tmp;
while ((tmp = sem->count) >= 0) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
return 1;
}
}
return 0;
}
/*
* lock for writing
*/
static inline void __down_write(struct rw_semaphore *sem)
{
int tmp;
tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count));
if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
rwsem_down_write_failed(sem);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
int 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)
{
int tmp;
tmp = atomic_dec_return((atomic_t *)(&sem->count));
if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count)) < 0))
rwsem_wake(sem);
}
/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
atomic_add(delta, (atomic_t *)(&sem->count));
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
int tmp;
tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
if (tmp < 0)
rwsem_downgrade_wake(sem);
}
/*
* implement exchange and add functionality
*/
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
return atomic_add_return(delta, (atomic_t *)(&sem->count));
}
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
return (sem->count != 0);
}
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_RWSEM_H */