kref.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * kref.h - library routines for handling generic reference counted objects
  4 *
  5 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
  6 * Copyright (C) 2004 IBM Corp.
  7 *
  8 * based on kobject.h which was:
  9 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
 10 * Copyright (C) 2002-2003 Open Source Development Labs
 11 */
 12
 13#ifndef _KREF_H_
 14#define _KREF_H_
 15
 16#include <linux/spinlock.h>
 17#include <linux/refcount.h>
 18
 19struct kref {
 20	refcount_t refcount;
 21};
 22
 23#define KREF_INIT(n)	{ .refcount = REFCOUNT_INIT(n), }
 24
 25/**
 26 * kref_init - initialize object.
 27 * @kref: object in question.
 28 */
 29static inline void kref_init(struct kref *kref)
 30{
 31	refcount_set(&kref->refcount, 1);
 32}
 33
 34static inline unsigned int kref_read(const struct kref *kref)
 35{
 36	return refcount_read(&kref->refcount);
 37}
 38
 39/**
 40 * kref_get - increment refcount for object.
 41 * @kref: object.
 42 */
 43static inline void kref_get(struct kref *kref)
 44{
 45	refcount_inc(&kref->refcount);
 46}
 47
 48/**
 49 * kref_put - Decrement refcount for object
 50 * @kref: Object
 51 * @release: Pointer to the function that will clean up the object when the
 52 *	     last reference to the object is released.
 53 *
 54 * Decrement the refcount, and if 0, call @release.  The caller may not
 55 * pass NULL or kfree() as the release function.
 56 *
 57 * Return: 1 if this call removed the object, otherwise return 0.  Beware,
 58 * if this function returns 0, another caller may have removed the object
 59 * by the time this function returns.  The return value is only certain
 60 * if you want to see if the object is definitely released.
 61 */
 62static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 63{
 64	if (refcount_dec_and_test(&kref->refcount)) {
 65		release(kref);
 66		return 1;
 67	}
 68	return 0;
 69}
 70
 71/**
 72 * kref_put_mutex - Decrement refcount for object
 73 * @kref: Object
 74 * @release: Pointer to the function that will clean up the object when the
 75 *	     last reference to the object is released.
 76 * @mutex: Mutex which protects the release function.
 77 *
 78 * This variant of kref_lock() calls the @release function with the @mutex
 79 * held.  The @release function will release the mutex.
 80 */
 81static inline int kref_put_mutex(struct kref *kref,
 82				 void (*release)(struct kref *kref),
 83				 struct mutex *mutex)
 84{
 85	if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
 86		release(kref);
 87		return 1;
 88	}
 89	return 0;
 90}
 91
 92/**
 93 * kref_put_lock - Decrement refcount for object
 94 * @kref: Object
 95 * @release: Pointer to the function that will clean up the object when the
 96 *	     last reference to the object is released.
 97 * @lock: Spinlock which protects the release function.
 98 *
 99 * This variant of kref_lock() calls the @release function with the @lock
100 * held.  The @release function will release the lock.
101 */
102static inline int kref_put_lock(struct kref *kref,
103				void (*release)(struct kref *kref),
104				spinlock_t *lock)
105{
106	if (refcount_dec_and_lock(&kref->refcount, lock)) {
107		release(kref);
108		return 1;
109	}
110	return 0;
111}
112
113/**
114 * kref_get_unless_zero - Increment refcount for object unless it is zero.
115 * @kref: object.
116 *
117 * This function is intended to simplify locking around refcounting for
118 * objects that can be looked up from a lookup structure, and which are
119 * removed from that lookup structure in the object destructor.
120 * Operations on such objects require at least a read lock around
121 * lookup + kref_get, and a write lock around kref_put + remove from lookup
122 * structure. Furthermore, RCU implementations become extremely tricky.
123 * With a lookup followed by a kref_get_unless_zero *with return value check*
124 * locking in the kref_put path can be deferred to the actual removal from
125 * the lookup structure and RCU lookups become trivial.
126 *
127 * Return: non-zero if the increment succeeded. Otherwise return 0.
128 */
129static inline int __must_check kref_get_unless_zero(struct kref *kref)
130{
131	return refcount_inc_not_zero(&kref->refcount);
132}
133#endif /* _KREF_H_ */