1 /* 2 * kref.h - library routines for handling generic reference counted objects 3 * 4 * Copyright (C) 2004 Greg Kroah-Hartman <[email protected]> 5 * Copyright (C) 2004 IBM Corp. 6 * 7 * based on kobject.h which was: 8 * Copyright (C) 2002-2003 Patrick Mochel <[email protected]> 9 * Copyright (C) 2002-2003 Open Source Development Labs 10 * 11 * This file is released under the GPLv2. 12 * 13 */ 14 15 #ifndef _KREF_H_ 16 #define _KREF_H_ 17 18 #include <linux/types.h> 19 #include <linux/slab.h> 20 21 struct kref { 22 atomic_t refcount; 23 }; 24 25 /** 26 * kref_init - initialize object. 27 * @kref: object in question. 28 */ 29 static inline void kref_init(struct kref *kref) 30 { 31 atomic_set(&kref->refcount, 1); 32 smp_mb(); 33 } 34 35 /** 36 * kref_get - increment refcount for object. 37 * @kref: object. 38 */ 39 static inline void kref_get(struct kref *kref) 40 { 41 WARN_ON(!atomic_read(&kref->refcount)); 42 atomic_inc(&kref->refcount); 43 smp_mb__after_atomic_inc(); 44 } 45 46 /** 47 * kref_sub - subtract a number of refcounts for object. 48 * @kref: object. 49 * @count: Number of recounts to subtract. 50 * @release: pointer to the function that will clean up the object when the 51 * last reference to the object is released. 52 * This pointer is required, and it is not acceptable to pass kfree 53 * in as this function. 54 * 55 * Subtract @count from the refcount, and if 0, call release(). 56 * Return 1 if the object was removed, otherwise return 0. Beware, if this 57 * function returns 0, you still can not count on the kref from remaining in 58 * memory. Only use the return value if you want to see if the kref is now 59 * gone, not present. 60 */ 61 static inline int kref_sub(struct kref *kref, unsigned int count, 62 void (*release)(struct kref *kref)) 63 { 64 WARN_ON(release == NULL); 65 WARN_ON(release == (void (*)(struct kref *))kfree); 66 67 if (atomic_sub_and_test((int) count, &kref->refcount)) { 68 release(kref); 69 return 1; 70 } 71 return 0; 72 } 73 74 /** 75 * kref_put - decrement refcount for object. 76 * @kref: object. 77 * @release: pointer to the function that will clean up the object when the 78 * last reference to the object is released. 79 * This pointer is required, and it is not acceptable to pass kfree 80 * in as this function. 81 * 82 * Decrement the refcount, and if 0, call release(). 83 * Return 1 if the object was removed, otherwise return 0. Beware, if this 84 * function returns 0, you still can not count on the kref from remaining in 85 * memory. Only use the return value if you want to see if the kref is now 86 * gone, not present. 87 */ 88 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) 89 { 90 return kref_sub(kref, 1, release); 91 } 92 #endif /* _KREF_H_ */ 93