1 #ifndef __LINUX_LOCKREF_H 2 #define __LINUX_LOCKREF_H 3 4 /* 5 * Locked reference counts. 6 * 7 * These are different from just plain atomic refcounts in that they 8 * are atomic with respect to the spinlock that goes with them. In 9 * particular, there can be implementations that don't actually get 10 * the spinlock for the common decrement/increment operations, but they 11 * still have to check that the operation is done semantically as if 12 * the spinlock had been taken (using a cmpxchg operation that covers 13 * both the lock and the count word, or using memory transactions, for 14 * example). 15 */ 16 17 #include <linux/spinlock.h> 18 19 struct lockref { 20 spinlock_t lock; 21 unsigned int count; 22 }; 23 24 /** 25 * lockref_get - Increments reference count unconditionally 26 * @lockcnt: pointer to lockref structure 27 * 28 * This operation is only valid if you already hold a reference 29 * to the object, so you know the count cannot be zero. 30 */ 31 static inline void lockref_get(struct lockref *lockref) 32 { 33 spin_lock(&lockref->lock); 34 lockref->count++; 35 spin_unlock(&lockref->lock); 36 } 37 38 /** 39 * lockref_get_not_zero - Increments count unless the count is 0 40 * @lockcnt: pointer to lockref structure 41 * Return: 1 if count updated successfully or 0 if count is 0 42 */ 43 static inline int lockref_get_not_zero(struct lockref *lockref) 44 { 45 int retval = 0; 46 47 spin_lock(&lockref->lock); 48 if (lockref->count) { 49 lockref->count++; 50 retval = 1; 51 } 52 spin_unlock(&lockref->lock); 53 return retval; 54 } 55 56 /** 57 * lockref_put_or_lock - decrements count unless count <= 1 before decrement 58 * @lockcnt: pointer to lockref structure 59 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken 60 */ 61 static inline int lockref_put_or_lock(struct lockref *lockref) 62 { 63 spin_lock(&lockref->lock); 64 if (lockref->count <= 1) 65 return 0; 66 lockref->count--; 67 spin_unlock(&lockref->lock); 68 return 1; 69 } 70 71 #endif /* __LINUX_LOCKREF_H */ 72