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