LXR linux/include/linux/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 *           This pointer is required, and it is not acceptable to pass kfree
  54 *           in as this function.
  55 *
  56 * Decrement the refcount, and if 0, call release().
  57 * Return 1 if the object was removed, otherwise return 0.  Beware, if this
  58 * function returns 0, you still can not count on the kref from remaining in
  59 * memory.  Only use the return value if you want to see if the kref is now
  60 * gone, not present.
  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
  71static inline int kref_put_mutex(struct kref *kref,
  72                                 void (*release)(struct kref *kref),
  73                                 struct mutex *lock)
  74{
  75        if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
  76                release(kref);
  77                return 1;
  78        }
  79        return 0;
  80}
  81
  82static inline int kref_put_lock(struct kref *kref,
  83                                void (*release)(struct kref *kref),
  84                                spinlock_t *lock)
  85{
  86        if (refcount_dec_and_lock(&kref->refcount, lock)) {
  87                release(kref);
  88                return 1;
  89        }
  90        return 0;
  91}
  92
  93/**
  94 * kref_get_unless_zero - Increment refcount for object unless it is zero.
  95 * @kref: object.
  96 *
  97 * Return non-zero if the increment succeeded. Otherwise return 0.
  98 *
  99 * This function is intended to simplify locking around refcounting for
 100 * objects that can be looked up from a lookup structure, and which are
 101 * removed from that lookup structure in the object destructor.
 102 * Operations on such objects require at least a read lock around
 103 * lookup + kref_get, and a write lock around kref_put + remove from lookup
 104 * structure. Furthermore, RCU implementations become extremely tricky.
 105 * With a lookup followed by a kref_get_unless_zero *with return value check*
 106 * locking in the kref_put path can be deferred to the actual removal from
 107 * the lookup structure and RCU lookups become trivial.
 108 */
 109static inline int __must_check kref_get_unless_zero(struct kref *kref)
 110{
 111        return refcount_inc_not_zero(&kref->refcount);
 112}
 113#endif /* _KREF_H_ */
 114