| 1 | |
| 2 | * kref.h - library routines for handling generic reference counted objects
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| 3 | *
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| 4 | * Copyright (C) 2004 Greg Kroah-Hartman <[email protected]>
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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 <[email protected]>
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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 |
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| 15 | #ifndef _KREF_H_
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| 16 | #define _KREF_H_
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| 17 |
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| 18 | #include <linux/spinlock.h>
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| 19 | #include <linux/refcount.h>
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| 20 |
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| 21 | struct kref {
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| 22 | refcount_t refcount;
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| 23 | };
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| 24 |
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| 25 | #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
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| 26 |
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| 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 | refcount_set(&kref->refcount, 1);
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| 34 | }
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| 35 |
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| 36 | static inline unsigned int kref_read(const struct kref *kref)
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| 37 | {
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| 38 | return refcount_read(&kref->refcount);
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| 39 | }
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| 40 |
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| 41 | |
| 42 | * kref_get - increment refcount for object.
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| 43 | * @kref: object.
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| 44 |
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| 45 | static inline void kref_get(struct kref *kref)
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| 46 | {
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| 47 | refcount_inc(&kref->refcount);
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| 48 | }
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| 49 |
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| 50 | |
| 51 | * kref_put - decrement refcount for object.
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| 52 | * @kref: object.
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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 | * Decrement 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_put(struct kref *kref, void (*release)(struct kref *kref))
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| 68 | {
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| 69 | if (refcount_dec_and_test(&kref->refcount)) {
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| 70 | release(kref);
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| 71 | return 1;
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| 72 | }
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| 73 | return 0;
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| 74 | }
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| 75 |
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| 76 | static inline int kref_put_mutex(struct kref *kref,
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| 77 | void (*release)(struct kref *kref),
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| 78 | struct mutex *lock)
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| 79 | {
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| 80 | if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
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| 81 | release(kref);
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| 82 | return 1;
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| 83 | }
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| 84 | return 0;
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| 85 | }
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| 86 |
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| 87 | static inline int kref_put_lock(struct kref *kref,
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| 88 | void (*release)(struct kref *kref),
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| 89 | spinlock_t *lock)
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| 90 | {
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| 91 | if (refcount_dec_and_lock(&kref->refcount, lock)) {
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| 92 | release(kref);
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| 93 | return 1;
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| 94 | }
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| 95 | return 0;
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| 96 | }
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| 97 |
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| 98 | |
| 99 | * kref_get_unless_zero - Increment refcount for object unless it is zero.
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| 100 | * @kref: object.
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| 101 | *
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| 102 | * Return non-zero if the increment succeeded. Otherwise return 0.
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| 103 | *
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| 104 | * This function is intended to simplify locking around refcounting for
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| 105 | * objects that can be looked up from a lookup structure, and which are
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| 106 | * removed from that lookup structure in the object destructor.
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| 107 | * Operations on such objects require at least a read lock around
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| 108 | * lookup + kref_get, and a write lock around kref_put + remove from lookup
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| 109 | * structure. Furthermore, RCU implementations become extremely tricky.
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| 110 | * With a lookup followed by a kref_get_unless_zero *with return value check*
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| 111 | * locking in the kref_put path can be deferred to the actual removal from
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| 112 | * the lookup structure and RCU lookups become trivial.
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| 113 |
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| 114 | static inline int __must_check kref_get_unless_zero(struct kref *kref)
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| 115 | {
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| 116 | return refcount_inc_not_zero(&kref->refcount);
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| 117 | }
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| 118 | #endif
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