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include/linux/kref.h
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/* |
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* kref.h - library routines for handling generic reference counted objects |
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* * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com> * Copyright (C) 2004 IBM Corp. * * based on kobject.h which was: * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org> * Copyright (C) 2002-2003 Open Source Development Labs * * This file is released under the GPLv2. * */ #ifndef _KREF_H_ #define _KREF_H_ |
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#include <linux/bug.h> #include <linux/atomic.h> |
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#include <linux/kernel.h> |
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#include <linux/mutex.h> |
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struct kref { atomic_t refcount; }; |
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/** * kref_init - initialize object. * @kref: object in question. */ static inline void kref_init(struct kref *kref) { atomic_set(&kref->refcount, 1); |
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} /** * kref_get - increment refcount for object. * @kref: object. */ static inline void kref_get(struct kref *kref) { |
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/* If refcount was 0 before incrementing then we have a race * condition when this kref is freeing by some other thread right now. * In this case one should use kref_get_unless_zero() */ WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); |
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} /** |
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* kref_sub - subtract a number of refcounts for object. |
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* @kref: object. |
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* @count: Number of recounts to subtract. |
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* @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree |
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* in as this function. If the caller does pass kfree to this * function, you will be publicly mocked mercilessly by the kref * maintainer, and anyone else who happens to notice it. You have * been warned. |
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* |
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* Subtract @count from the refcount, and if 0, call release(). |
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* Return 1 if the object was removed, otherwise return 0. Beware, if this * function returns 0, you still can not count on the kref from remaining in * memory. Only use the return value if you want to see if the kref is now * gone, not present. */ |
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static inline int kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *kref)) |
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{ WARN_ON(release == NULL); |
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|
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if (atomic_sub_and_test((int) count, &kref->refcount)) { |
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release(kref); return 1; } return 0; } |
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/** |
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* kref_put - decrement refcount for object. |
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* @kref: object. |
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* @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree |
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* in as this function. If the caller does pass kfree to this * function, you will be publicly mocked mercilessly by the kref * maintainer, and anyone else who happens to notice it. You have * been warned. |
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* |
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* Decrement the refcount, and if 0, call release(). |
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* Return 1 if the object was removed, otherwise return 0. Beware, if this * function returns 0, you still can not count on the kref from remaining in * memory. Only use the return value if you want to see if the kref is now * gone, not present. */ |
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static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
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{ |
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return kref_sub(kref, 1, release); |
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} |
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static inline int kref_put_mutex(struct kref *kref, void (*release)(struct kref *kref), struct mutex *lock) { WARN_ON(release == NULL); |
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if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { |
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mutex_lock(lock); if (unlikely(!atomic_dec_and_test(&kref->refcount))) { mutex_unlock(lock); return 0; } release(kref); return 1; } return 0; } |
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/** * kref_get_unless_zero - Increment refcount for object unless it is zero. * @kref: object. * * Return non-zero if the increment succeeded. Otherwise return 0. * * This function is intended to simplify locking around refcounting for * objects that can be looked up from a lookup structure, and which are * removed from that lookup structure in the object destructor. * Operations on such objects require at least a read lock around * lookup + kref_get, and a write lock around kref_put + remove from lookup * structure. Furthermore, RCU implementations become extremely tricky. * With a lookup followed by a kref_get_unless_zero *with return value check* * locking in the kref_put path can be deferred to the actual removal from * the lookup structure and RCU lookups become trivial. */ static inline int __must_check kref_get_unless_zero(struct kref *kref) { return atomic_add_unless(&kref->refcount, 1, 0); } |
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#endif /* _KREF_H_ */ |