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| Rev | Author | Line No. | Line |
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| 1408 | serge | 1 | /* |
| 1964 | serge | 2 | * kref.h - library routines for handling generic reference counted objects |
| 1408 | serge | 3 | * |
| 4 | * Copyright (C) 2004 Greg Kroah-Hartman |
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| 5 | * Copyright (C) 2004 IBM Corp. |
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| 6 | * |
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| 7 | * based on kobject.h which was: |
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| 8 | * Copyright (C) 2002-2003 Patrick Mochel |
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| 9 | * Copyright (C) 2002-2003 Open Source Development Labs |
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| 10 | * |
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| 11 | * This file is released under the GPLv2. |
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| 12 | * |
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| 13 | */ |
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| 14 | |||
| 15 | #ifndef _KREF_H_ |
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| 16 | #define _KREF_H_ |
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| 17 | |||
| 5270 | serge | 18 | #include |
| 19 | #include |
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| 20 | #include |
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| 21 | #include |
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| 1408 | serge | 22 | |
| 23 | struct kref { |
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| 24 | atomic_t refcount; |
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| 25 | }; |
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| 26 | |||
| 6082 | serge | 27 | /** |
| 28 | * kref_init - initialize object. |
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| 29 | * @kref: object in question. |
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| 30 | */ |
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| 31 | static inline void kref_init(struct kref *kref) |
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| 32 | { |
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| 33 | atomic_set(&kref->refcount, 1); |
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| 34 | } |
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| 1408 | serge | 35 | |
| 6082 | serge | 36 | /** |
| 37 | * kref_get - increment refcount for object. |
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| 38 | * @kref: object. |
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| 39 | */ |
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| 40 | static inline void kref_get(struct kref *kref) |
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| 41 | { |
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| 42 | /* If refcount was 0 before incrementing then we have a race |
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| 43 | * condition when this kref is freeing by some other thread right now. |
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| 44 | * In this case one should use kref_get_unless_zero() |
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| 45 | */ |
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| 46 | WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); |
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| 47 | } |
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| 48 | |||
| 49 | /** |
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| 50 | * kref_sub - subtract a number of refcounts for object. |
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| 51 | * @kref: object. |
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| 52 | * @count: Number of recounts to subtract. |
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| 53 | * @release: pointer to the function that will clean up the object when the |
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| 54 | * last reference to the object is released. |
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| 55 | * This pointer is required, and it is not acceptable to pass kfree |
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| 56 | * in as this function. If the caller does pass kfree to this |
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| 57 | * function, you will be publicly mocked mercilessly by the kref |
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| 58 | * maintainer, and anyone else who happens to notice it. You have |
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| 59 | * been warned. |
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| 60 | * |
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| 61 | * Subtract @count from the refcount, and if 0, call release(). |
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| 62 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
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| 63 | * function returns 0, you still can not count on the kref from remaining in |
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| 64 | * memory. Only use the return value if you want to see if the kref is now |
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| 65 | * gone, not present. |
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| 66 | */ |
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| 67 | static inline int kref_sub(struct kref *kref, unsigned int count, |
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| 68 | void (*release)(struct kref *kref)) |
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| 69 | { |
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| 70 | WARN_ON(release == NULL); |
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| 71 | |||
| 72 | if (atomic_sub_and_test((int) count, &kref->refcount)) { |
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| 73 | release(kref); |
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| 74 | return 1; |
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| 75 | } |
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| 76 | return 0; |
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| 77 | } |
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| 78 | |||
| 79 | /** |
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| 80 | * kref_put - decrement refcount for object. |
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| 81 | * @kref: object. |
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| 82 | * @release: pointer to the function that will clean up the object when the |
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| 83 | * last reference to the object is released. |
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| 84 | * This pointer is required, and it is not acceptable to pass kfree |
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| 85 | * in as this function. If the caller does pass kfree to this |
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| 86 | * function, you will be publicly mocked mercilessly by the kref |
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| 87 | * maintainer, and anyone else who happens to notice it. You have |
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| 88 | * been warned. |
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| 89 | * |
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| 90 | * Decrement the refcount, and if 0, call release(). |
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| 91 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
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| 92 | * function returns 0, you still can not count on the kref from remaining in |
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| 93 | * memory. Only use the return value if you want to see if the kref is now |
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| 94 | * gone, not present. |
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| 95 | */ |
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| 96 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
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| 97 | { |
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| 98 | return kref_sub(kref, 1, release); |
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| 99 | } |
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| 100 | |||
| 101 | static inline int kref_put_mutex(struct kref *kref, |
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| 102 | void (*release)(struct kref *kref), |
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| 103 | struct mutex *lock) |
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| 104 | { |
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| 105 | WARN_ON(release == NULL); |
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| 106 | if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { |
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| 107 | mutex_lock(lock); |
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| 108 | if (unlikely(!atomic_dec_and_test(&kref->refcount))) { |
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| 109 | mutex_unlock(lock); |
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| 110 | return 0; |
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| 111 | } |
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| 112 | release(kref); |
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| 113 | return 1; |
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| 114 | } |
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| 115 | return 0; |
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| 116 | } |
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| 117 | |||
| 118 | /** |
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| 119 | * kref_get_unless_zero - Increment refcount for object unless it is zero. |
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| 120 | * @kref: object. |
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| 121 | * |
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| 122 | * Return non-zero if the increment succeeded. Otherwise return 0. |
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| 123 | * |
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| 124 | * This function is intended to simplify locking around refcounting for |
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| 125 | * objects that can be looked up from a lookup structure, and which are |
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| 126 | * removed from that lookup structure in the object destructor. |
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| 127 | * Operations on such objects require at least a read lock around |
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| 128 | * lookup + kref_get, and a write lock around kref_put + remove from lookup |
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| 129 | * structure. Furthermore, RCU implementations become extremely tricky. |
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| 130 | * With a lookup followed by a kref_get_unless_zero *with return value check* |
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| 131 | * locking in the kref_put path can be deferred to the actual removal from |
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| 132 | * the lookup structure and RCU lookups become trivial. |
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| 133 | */ |
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| 134 | static inline int __must_check kref_get_unless_zero(struct kref *kref) |
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| 135 | { |
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| 136 | return atomic_add_unless(&kref->refcount, 1, 0); |
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| 137 | } |
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| 1408 | serge | 138 | #endif /* _KREF_H_ */ |