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- /* SPDX-License-Identifier: GPL-2.0-only */
- /*
- * kref.h - library routines for handling generic reference counted objects
- *
- * Copyright (C) 2004 Greg Kroah-Hartman <[email protected]>
- * Copyright (C) 2004 IBM Corp.
- *
- * based on kobject.h which was:
- * Copyright (C) 2002-2003 Patrick Mochel <[email protected]>
- * Copyright (C) 2002-2003 Open Source Development Labs
- */
- #ifndef _KREF_H_
- #define _KREF_H_
- #include <linux/spinlock.h>
- #include <linux/refcount.h>
- struct kref {
- refcount_t refcount;
- };
- #define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
- /**
- * kref_init - initialize object.
- * @kref: object in question.
- */
- static inline void kref_init(struct kref *kref)
- {
- refcount_set(&kref->refcount, 1);
- }
- static inline unsigned int kref_read(const struct kref *kref)
- {
- return refcount_read(&kref->refcount);
- }
- /**
- * kref_get - increment refcount for object.
- * @kref: object.
- */
- static inline void kref_get(struct kref *kref)
- {
- refcount_inc(&kref->refcount);
- }
- /**
- * kref_put - decrement refcount for object.
- * @kref: object.
- * @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
- * in as this function.
- *
- * Decrement the refcount, and if 0, call release().
- * 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.
- */
- static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
- {
- if (refcount_dec_and_test(&kref->refcount)) {
- release(kref);
- return 1;
- }
- return 0;
- }
- static inline int kref_put_mutex(struct kref *kref,
- void (*release)(struct kref *kref),
- struct mutex *lock)
- {
- if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
- release(kref);
- return 1;
- }
- return 0;
- }
- static inline int kref_put_lock(struct kref *kref,
- void (*release)(struct kref *kref),
- spinlock_t *lock)
- {
- if (refcount_dec_and_lock(&kref->refcount, lock)) {
- release(kref);
- return 1;
- }
- return 0;
- }
- /**
- * 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 refcount_inc_not_zero(&kref->refcount);
- }
- #endif /* _KREF_H_ */
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