88 lines
2.2 KiB
C
88 lines
2.2 KiB
C
#ifndef __LINUX_LOCKREF_H
|
|
#define __LINUX_LOCKREF_H
|
|
|
|
/*
|
|
* Locked reference counts.
|
|
*
|
|
* These are different from just plain atomic refcounts in that they
|
|
* are atomic with respect to the spinlock that goes with them. In
|
|
* particular, there can be implementations that don't actually get
|
|
* the spinlock for the common decrement/increment operations, but they
|
|
* still have to check that the operation is done semantically as if
|
|
* the spinlock had been taken (using a cmpxchg operation that covers
|
|
* both the lock and the count word, or using memory transactions, for
|
|
* example).
|
|
*/
|
|
|
|
#include <linux/spinlock.h>
|
|
|
|
struct lockref {
|
|
spinlock_t lock;
|
|
unsigned int count;
|
|
};
|
|
|
|
/**
|
|
* lockref_get - Increments reference count unconditionally
|
|
* @lockcnt: pointer to lockref structure
|
|
*
|
|
* This operation is only valid if you already hold a reference
|
|
* to the object, so you know the count cannot be zero.
|
|
*/
|
|
static inline void lockref_get(struct lockref *lockref)
|
|
{
|
|
spin_lock(&lockref->lock);
|
|
lockref->count++;
|
|
spin_unlock(&lockref->lock);
|
|
}
|
|
|
|
/**
|
|
* lockref_get_not_zero - Increments count unless the count is 0
|
|
* @lockcnt: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count is 0
|
|
*/
|
|
static inline int lockref_get_not_zero(struct lockref *lockref)
|
|
{
|
|
int retval = 0;
|
|
|
|
spin_lock(&lockref->lock);
|
|
if (lockref->count) {
|
|
lockref->count++;
|
|
retval = 1;
|
|
}
|
|
spin_unlock(&lockref->lock);
|
|
return retval;
|
|
}
|
|
|
|
/**
|
|
* lockref_get_or_lock - Increments count unless the count is 0
|
|
* @lockcnt: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count was zero
|
|
* and we got the lock instead.
|
|
*/
|
|
static inline int lockref_get_or_lock(struct lockref *lockref)
|
|
{
|
|
spin_lock(&lockref->lock);
|
|
if (!lockref->count)
|
|
return 0;
|
|
lockref->count++;
|
|
spin_unlock(&lockref->lock);
|
|
return 1;
|
|
}
|
|
|
|
/**
|
|
* lockref_put_or_lock - decrements count unless count <= 1 before decrement
|
|
* @lockcnt: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
|
|
*/
|
|
static inline int lockref_put_or_lock(struct lockref *lockref)
|
|
{
|
|
spin_lock(&lockref->lock);
|
|
if (lockref->count <= 1)
|
|
return 0;
|
|
lockref->count--;
|
|
spin_unlock(&lockref->lock);
|
|
return 1;
|
|
}
|
|
|
|
#endif /* __LINUX_LOCKREF_H */
|