seqc.h

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    1 /*-
    2  * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
    3  *
    4  * Redistribution and use in source and binary forms, with or without
    5  * modification, are permitted provided that the following conditions
    6  * are met:
    7  * 1. Redistributions of source code must retain the above copyright
    8  *    notice, this list of conditions and the following disclaimer.
    9  * 2. Redistributions in binary form must reproduce the above copyright
   10  *    notice, this list of conditions and the following disclaimer in the
   11  *    documentation and/or other materials provided with the distribution.
   12  *
   13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   14  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   16  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   17  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   18  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   19  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   20  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   21  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   22  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   23  * SUCH DAMAGE.
   24  *
   25  * $FreeBSD$
   26  */
   27 
   28 #ifndef _SYS_SEQC_H_
   29 #define _SYS_SEQC_H_
   30 
   31 #ifdef _KERNEL
   32 #include <sys/systm.h>
   33 #endif
   34 #include <sys/types.h>
   35 
   36 /*
   37  * seqc_t may be included in structs visible to userspace
   38  */
   39 #include <sys/_seqc.h>
   40 
   41 #ifdef _KERNEL
   42 
   43 /* A hack to get MPASS macro */
   44 #include <sys/lock.h>
   45 
   46 #include <machine/cpu.h>
   47 
   48 #define SEQC_MOD        1
   49 
   50 /*
   51  * Predicts from inline functions are not honored by clang.
   52  */
   53 #define seqc_in_modify(seqc)    ({                      \
   54         seqc_t __seqc = (seqc);                         \
   55                                                         \
   56         __predict_false(__seqc & SEQC_MOD);             \
   57 })
   58 
   59 static __inline void
   60 seqc_write_begin(seqc_t *seqcp)
   61 {
   62 
   63         critical_enter();
   64         MPASS(!seqc_in_modify(*seqcp));
   65         *seqcp += SEQC_MOD;
   66         atomic_thread_fence_rel();
   67 }
   68 
   69 static __inline void
   70 seqc_write_end(seqc_t *seqcp)
   71 {
   72 
   73         atomic_thread_fence_rel();
   74         *seqcp += SEQC_MOD;
   75         MPASS(!seqc_in_modify(*seqcp));
   76         critical_exit();
   77 }
   78 
   79 static __inline seqc_t
   80 seqc_read_any(const seqc_t *seqcp)
   81 {
   82 
   83         return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)));
   84 }
   85 
   86 static __inline seqc_t
   87 seqc_read_notmodify(const seqc_t *seqcp)
   88 {
   89 
   90         return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)) & ~SEQC_MOD);
   91 }
   92 
   93 static __inline seqc_t
   94 seqc_read(const seqc_t *seqcp)
   95 {
   96         seqc_t ret;
   97 
   98         for (;;) {
   99                 ret = seqc_read_any(seqcp);
  100                 if (seqc_in_modify(ret)) {
  101                         cpu_spinwait();
  102                         continue;
  103                 }
  104                 break;
  105         }
  106 
  107         return (ret);
  108 }
  109 
  110 #define seqc_consistent_no_fence(seqcp, oldseqc)({      \
  111         const seqc_t *__seqcp = (seqcp);                \
  112         seqc_t __oldseqc = (oldseqc);                   \
  113                                                         \
  114         MPASS(!(seqc_in_modify(__oldseqc)));            \
  115         __predict_true(*__seqcp == __oldseqc);          \
  116 })
  117 
  118 #define seqc_consistent(seqcp, oldseqc)         ({      \
  119         atomic_thread_fence_acq();                      \
  120         seqc_consistent_no_fence(seqcp, oldseqc);       \
  121 })
  122 
  123 /*
  124  * Variant which does not critical enter/exit.
  125  */
  126 static __inline void
  127 seqc_sleepable_write_begin(seqc_t *seqcp)
  128 {
  129 
  130         MPASS(!seqc_in_modify(*seqcp));
  131         *seqcp += SEQC_MOD;
  132         atomic_thread_fence_rel();
  133 }
  134 
  135 static __inline void
  136 seqc_sleepable_write_end(seqc_t *seqcp)
  137 {
  138 
  139         atomic_thread_fence_rel();
  140         *seqcp += SEQC_MOD;
  141         MPASS(!seqc_in_modify(*seqcp));
  142 }
  143 
  144 #endif  /* _KERNEL */
  145 #endif  /* _SYS_SEQC_H_ */

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FreeBSD/Linux Kernel Cross Reference sys/sys/seqc.h

FreeBSD/Linux Kernel Cross Reference
sys/sys/seqc.h