sys/kern/kern_ref.c

   1 /*
   2  * Copyright (c) 2010, Venkatesh Srinivas <me@endeavour.zapto.org>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 /*
  18  * Lightweight reference counts
  19  */
  20
  21 #include <cpu/atomic.h>
  22 #include <sys/ref.h>
  23
  24 void
  25 kref_init(struct kref *ref, int count)
  26 {
  27         ref->refcount = count;
  28 }
  29
  30 void
  31 kref_inc(struct kref *ref)
  32 {
  33         atomic_add_int(&ref->refcount, 1);
  34 }
  35
  36 /*
  37  * Decrement a reference count; on a 1 -> 0 transition, call the
  38  * deconstruct function (if any) with priv1 and priv2. Returns 0
  39  * if it sees a 1 -> 0 transition, 1 otherwise.
  40  *
  41  * "An object cannot synchronize its own visibility." It is not safe
  42  * to interleave kref_inc and kref_dec without other synchronization.
  43  */
  44 int
  45 kref_dec(struct kref *ref, void (*deconstruct)(void *, void *),
  46          void *priv1, void *priv2)
  47 {
  48         int val;
  49
  50         val = atomic_fetchadd_int(&ref->refcount, -1);
  51         if (val == 1)  {
  52                 if (deconstruct)
  53                         deconstruct(priv1, priv2);
  54                 return (0);
  55         }
  56
  57         return (1);
  58 }