| 1 |
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| 2 | |
| 3 | * kref.h - library routines for handling generic reference counted objects
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| 4 | *
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| 5 | * Copyright (C) 2004 Greg Kroah-Hartman <[email protected]>
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| 6 | * Copyright (C) 2004 IBM Corp.
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| 7 | *
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| 8 | * based on kobject.h which was:
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| 9 | * Copyright (C) 2002-2003 Patrick Mochel <[email protected]>
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| 10 | * Copyright (C) 2002-2003 Open Source Development Labs
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| 11 |
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| 12 |
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| 13 | #ifndef _KREF_H_
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| 14 | #define _KREF_H_
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| 15 |
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| 16 | #include <linux/spinlock.h>
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| 17 | #include <linux/refcount.h>
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| 18 |
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| 19 | struct kref {
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| 20 | refcount_t refcount;
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| 21 | };
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| 22 |
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| 23 | #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
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| 24 |
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| 25 | |
| 26 | * kref_init - initialize object.
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| 27 | * @kref: object in question.
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| 28 |
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| 29 | static inline void kref_init(struct kref *kref)
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| 30 | {
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| 31 | refcount_set(&kref->refcount, 1);
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| 32 | }
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| 33 |
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| 34 | static inline unsigned int kref_read(const struct kref *kref)
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| 35 | {
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| 36 | return refcount_read(&kref->refcount);
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| 37 | }
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| 38 |
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| 39 | |
| 40 | * kref_get - increment refcount for object.
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| 41 | * @kref: object.
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| 42 |
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| 43 | static inline void kref_get(struct kref *kref)
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| 44 | {
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| 45 | refcount_inc(&kref->refcount);
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| 46 | }
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| 47 |
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| 48 | |
| 49 | * kref_put - Decrement refcount for object
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| 50 | * @kref: Object
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| 51 | * @release: Pointer to the function that will clean up the object when the
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| 52 | * last reference to the object is released.
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| 53 | *
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| 54 | * Decrement the refcount, and if 0, call @release. The caller may not
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| 55 | * pass NULL or kfree() as the release function.
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| 56 | *
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| 57 | * Return: 1 if this call removed the object, otherwise return 0. Beware,
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| 58 | * if this function returns 0, another caller may have removed the object
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| 59 | * by the time this function returns. The return value is only certain
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| 60 | * if you want to see if the object is definitely released.
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| 61 |
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| 62 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
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| 63 | {
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| 64 | if (refcount_dec_and_test(&kref->refcount)) {
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| 65 | release(kref);
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| 66 | return 1;
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| 67 | }
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| 68 | return 0;
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| 69 | }
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| 70 |
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| 71 | |
| 72 | * kref_put_mutex - Decrement refcount for object
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| 73 | * @kref: Object
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| 74 | * @release: Pointer to the function that will clean up the object when the
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| 75 | * last reference to the object is released.
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| 76 | * @mutex: Mutex which protects the release function.
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| 77 | *
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| 78 | * This variant of kref_lock() calls the @release function with the @mutex
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| 79 | * held. The @release function will release the mutex.
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| 80 |
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| 81 | static inline int kref_put_mutex(struct kref *kref,
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| 82 | void (*release)(struct kref *kref),
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| 83 | struct mutex *mutex)
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| 84 | __cond_acquires(true, mutex)
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| 85 | {
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| 86 | if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
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| 87 | release(kref);
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| 88 | return 1;
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| 89 | }
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| 90 | return 0;
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| 91 | }
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| 92 |
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| 93 | |
| 94 | * kref_put_lock - Decrement refcount for object
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| 95 | * @kref: Object
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| 96 | * @release: Pointer to the function that will clean up the object when the
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| 97 | * last reference to the object is released.
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| 98 | * @lock: Spinlock which protects the release function.
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| 99 | *
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| 100 | * This variant of kref_lock() calls the @release function with the @lock
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| 101 | * held. The @release function will release the lock.
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| 102 |
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| 103 | static inline int kref_put_lock(struct kref *kref,
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| 104 | void (*release)(struct kref *kref),
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| 105 | spinlock_t *lock)
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| 106 | __cond_acquires(true, lock)
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| 107 | {
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| 108 | if (refcount_dec_and_lock(&kref->refcount, lock)) {
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| 109 | release(kref);
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| 110 | return 1;
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| 111 | }
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| 112 | return 0;
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| 113 | }
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| 114 |
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| 115 | |
| 116 | * kref_get_unless_zero - Increment refcount for object unless it is zero.
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| 117 | * @kref: object.
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| 118 | *
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| 119 | * This function is intended to simplify locking around refcounting for
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| 120 | * objects that can be looked up from a lookup structure, and which are
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| 121 | * removed from that lookup structure in the object destructor.
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| 122 | * Operations on such objects require at least a read lock around
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| 123 | * lookup + kref_get, and a write lock around kref_put + remove from lookup
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| 124 | * structure. Furthermore, RCU implementations become extremely tricky.
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| 125 | * With a lookup followed by a kref_get_unless_zero *with return value check*
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| 126 | * locking in the kref_put path can be deferred to the actual removal from
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| 127 | * the lookup structure and RCU lookups become trivial.
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| 128 | *
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| 129 | * Return: non-zero if the increment succeeded. Otherwise return 0.
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| 130 |
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| 131 | static inline int __must_check kref_get_unless_zero(struct kref *kref)
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| 132 | {
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| 133 | return refcount_inc_not_zero(&kref->refcount);
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| 134 | }
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| 135 | #endif
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