Line data    Source code

       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             : 
      19             : struct 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             :  */
      29             : static inline void kref_init(struct kref *kref)
      30             : {
      31         272 :         refcount_set(&kref->refcount, 1);
      32             : }
      33             : 
      34             : static 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             :  */
      43             : static inline void kref_get(struct kref *kref)
      44             : {
      45       22554 :         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             :  */
      62         272 : static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
      63             : {
      64         272 :         if (refcount_dec_and_test(&kref->refcount)) {
      65         272 :                 release(kref);
      66         272 :                 return 1;
      67             :         }
      68             :         return 0;
      69             : }
      70             : 
      71             : static 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             : 
      82             : static 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             :  */
     109             : static 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_ */