1 /* 2 * kref.h - library routines for handling generic reference counted objects 3 * 4 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com> 5 * Copyright (C) 2004 IBM Corp. 6 * 7 * based on kobject.h which was: 8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org> 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/spinlock.h> 19 #include <linux/refcount.h> 20 21 struct kref { 22 refcount_t refcount; 23 }; 24 25 #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), } 26 27 /** 28 * kref_init - initialize object. 29 * @kref: object in question. 30 */ 31 static inline void kref_init(struct kref *kref) 32 { 33 refcount_set(&kref->refcount, 1); 34 } 35 36 static inline unsigned int kref_read(const struct kref *kref) 37 { 38 return refcount_read(&kref->refcount); 39 } 40 41 /** 42 * kref_get - increment refcount for object. 43 * @kref: object. 44 */ 45 static inline void kref_get(struct kref *kref) 46 { 47 refcount_inc(&kref->refcount); 48 } 49 50 /** 51 * kref_put - decrement refcount for object. 52 * @kref: object. 53 * @release: pointer to the function that will clean up the object when the 54 * last reference to the object is released. 55 * This pointer is required, and it is not acceptable to pass kfree 56 * in as this function. If the caller does pass kfree to this 57 * function, you will be publicly mocked mercilessly by the kref 58 * maintainer, and anyone else who happens to notice it. You have 59 * been warned. 60 * 61 * Decrement the refcount, and if 0, call release(). 62 * Return 1 if the object was removed, otherwise return 0. Beware, if this 63 * function returns 0, you still can not count on the kref from remaining in 64 * memory. Only use the return value if you want to see if the kref is now 65 * gone, not present. 66 */ 67 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) 68 { 69 if (refcount_dec_and_test(&kref->refcount)) { 70 release(kref); 71 return 1; 72 } 73 return 0; 74 } 75 76 static inline int kref_put_mutex(struct kref *kref, 77 void (*release)(struct kref *kref), 78 struct mutex *lock) 79 { 80 if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) { 81 release(kref); 82 return 1; 83 } 84 return 0; 85 } 86 87 static inline int kref_put_lock(struct kref *kref, 88 void (*release)(struct kref *kref), 89 spinlock_t *lock) 90 { 91 if (refcount_dec_and_lock(&kref->refcount, lock)) { 92 release(kref); 93 return 1; 94 } 95 return 0; 96 } 97 98 /** 99 * kref_get_unless_zero - Increment refcount for object unless it is zero. 100 * @kref: object. 101 * 102 * Return non-zero if the increment succeeded. Otherwise return 0. 103 * 104 * This function is intended to simplify locking around refcounting for 105 * objects that can be looked up from a lookup structure, and which are 106 * removed from that lookup structure in the object destructor. 107 * Operations on such objects require at least a read lock around 108 * lookup + kref_get, and a write lock around kref_put + remove from lookup 109 * structure. Furthermore, RCU implementations become extremely tricky. 110 * With a lookup followed by a kref_get_unless_zero *with return value check* 111 * locking in the kref_put path can be deferred to the actual removal from 112 * the lookup structure and RCU lookups become trivial. 113 */ 114 static inline int __must_check kref_get_unless_zero(struct kref *kref) 115 { 116 return refcount_inc_not_zero(&kref->refcount); 117 } 118 #endif /* _KREF_H_ */ 119