LCOV - code coverage report
Current view: top level - include/linux - kref.h (source / functions) Hit Total Coverage
Test: Real Lines: 8 14 57.1 %
Date: 2020-10-17 15:46:16 Functions: 1 3 33.3 %
Legend: Neither, QEMU, Real, Both Branches: 0 0 -

           Branch data     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                 :            :         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                 :          3 :         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                 :          3 : static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
      63                 :            : {
      64                 :          3 :         if (refcount_dec_and_test(&kref->refcount)) {
      65                 :          3 :                 release(kref);
      66                 :          3 :                 return 1;
      67                 :            :         }
      68                 :            :         return 0;
      69                 :            : }
      70                 :            : 
      71                 :          2 : static inline int kref_put_mutex(struct kref *kref,
      72                 :            :                                  void (*release)(struct kref *kref),
      73                 :            :                                  struct mutex *lock)
      74                 :            : {
      75                 :          2 :         if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
      76                 :          0 :                 release(kref);
      77                 :          0 :                 return 1;
      78                 :            :         }
      79                 :            :         return 0;
      80                 :            : }
      81                 :            : 
      82                 :          0 : static inline int kref_put_lock(struct kref *kref,
      83                 :            :                                 void (*release)(struct kref *kref),
      84                 :            :                                 spinlock_t *lock)
      85                 :            : {
      86                 :          0 :         if (refcount_dec_and_lock(&kref->refcount, lock)) {
      87                 :          0 :                 release(kref);
      88                 :          0 :                 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                 :          3 :         return refcount_inc_not_zero(&kref->refcount);
     112                 :            : }
     113                 :            : #endif /* _KREF_H_ */
    

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