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