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kref.h revision 1.3 
      1 /*	$NetBSD: kref.h,v 1.3 2014/07/16 20:56:25 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2013 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #ifndef _LINUX_KREF_H_
     33 #define _LINUX_KREF_H_
     34 
     35 #include <sys/types.h>
     36 #include <sys/atomic.h>
     37 #include <sys/systm.h>
     38 
     39 #include <linux/mutex.h>
     40 
     41 struct kref {
     42 	unsigned int kr_count;
     43 };
     44 
     45 static inline void
     46 kref_init(struct kref *kref)
     47 {
     48 	kref->kr_count = 1;
     49 }
     50 
     51 static inline void
     52 kref_get(struct kref *kref)
     53 {
     54 	const unsigned int count __unused =
     55 	    atomic_inc_uint_nv(&kref->kr_count);
     56 
     57 	KASSERTMSG((count > 1), "getting released kref");
     58 }
     59 
     60 static inline int
     61 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
     62 {
     63 	unsigned int old, new;
     64 
     65 	do {
     66 		old = kref->kr_count;
     67 		KASSERTMSG((count <= old), "overreleasing kref: %u - %u",
     68 		    old, count);
     69 		new = (old - count);
     70 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
     71 
     72 	if (new == 0) {
     73 		(*release)(kref);
     74 		return 1;
     75 	}
     76 
     77 	return 0;
     78 }
     79 
     80 static inline int
     81 kref_put(struct kref *kref, void (*release)(struct kref *))
     82 {
     83 
     84 	return kref_sub(kref, 1, release);
     85 }
     86 
     87 static inline int
     88 kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
     89     struct mutex *interlock)
     90 {
     91 	unsigned int old, new;
     92 
     93 	do {
     94 		old = kref->kr_count;
     95 		KASSERT(old > 0);
     96 		if (old == 1) {
     97 			mutex_lock(interlock);
     98 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
     99 				(*release)(kref);
    100 				return 1;
    101 			}
    102 			mutex_unlock(interlock);
    103 			return 0;
    104 		}
    105 		new = (old - 1);
    106 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    107 
    108 	return 0;
    109 }
    110 
    111 /* Not native to Linux.  */
    112 static inline bool
    113 kref_exclusive_p(struct kref *kref)
    114 {
    115 
    116 	KASSERT(0 < kref->kr_count);
    117 	return (kref->kr_count == 1);
    118 }
    119 
    120 #endif  /* _LINUX_KREF_H_ */
    121