| 1 | /*
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| 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 <greg@kroah.com>
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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 <mochel@osdl.org>
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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 <asm/atomic.h>
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| 19 | #include <linux/kernel.h>
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| 20 | #include <linux/mutex.h>
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| 21 | #include <linux/spinlock.h>
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| 22 |
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| 23 | struct kref {
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| 24 | atomic_t refcount;
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| 25 | };
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| 26 |
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| 27 | /**
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| 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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| 35 |
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| 36 | /**
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| 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(atomic_inc_return(&kref->refcount) < 2);
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| 47 | }
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| 48 |
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| 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 |
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| 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 |
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| 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 |
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| 101 |
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| 102 | #endif /* _KREF_H_ */
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