/*-
 * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef _SYS_SEQC_H_
#define _SYS_SEQC_H_

#ifdef _KERNEL
#include <sys/systm.h>
#endif
#include <sys/types.h>

/*
 * seqc_t may be included in structs visible to userspace
 */
#include <sys/_seqc.h>

#ifdef _KERNEL

/* A hack to get MPASS macro */
#include <sys/lock.h>

#include <machine/cpu.h>

#define SEQC_MOD        1

/*
 * Predicts from inline functions are not honored by clang.
 */
#define seqc_in_modify(seqc)    ({                      \
        seqc_t __seqc = (seqc);                         \
                                                        \
        __predict_false(__seqc & SEQC_MOD);             \
})

static __inline void
seqc_write_begin(seqc_t *seqcp)
{

        critical_enter();
        MPASS(!seqc_in_modify(*seqcp));
        *seqcp += SEQC_MOD;
        atomic_thread_fence_rel();
}

static __inline void
seqc_write_end(seqc_t *seqcp)
{

        atomic_thread_fence_rel();
        *seqcp += SEQC_MOD;
        MPASS(!seqc_in_modify(*seqcp));
        critical_exit();
}

static __inline seqc_t
seqc_read_any(const seqc_t *seqcp)
{

        return (atomic_load_acq_int(seqcp));
}

static __inline seqc_t
seqc_read_notmodify(const seqc_t *seqcp)
{

        return (atomic_load_acq_int(seqcp) & ~SEQC_MOD);
}

static __inline seqc_t
seqc_read(const seqc_t *seqcp)
{
        seqc_t ret;

        for (;;) {
                ret = seqc_read_any(seqcp);
                if (seqc_in_modify(ret)) {
                        cpu_spinwait();
                        continue;
                }
                break;
        }

        return (ret);
}

#define seqc_consistent_no_fence(seqcp, oldseqc)({      \
        const seqc_t *__seqcp = (seqcp);                \
        seqc_t __oldseqc = (oldseqc);                   \
                                                        \
        MPASS(!(seqc_in_modify(__oldseqc)));            \
        __predict_true(*__seqcp == __oldseqc);          \
})

#define seqc_consistent(seqcp, oldseqc)         ({      \
        atomic_thread_fence_acq();                      \
        seqc_consistent_no_fence(seqcp, oldseqc);       \
})

/*
 * Variant which does not critical enter/exit.
 */
static __inline void
seqc_sleepable_write_begin(seqc_t *seqcp)
{

        MPASS(!seqc_in_modify(*seqcp));
        *seqcp += SEQC_MOD;
        atomic_thread_fence_rel();
}

static __inline void
seqc_sleepable_write_end(seqc_t *seqcp)
{

        atomic_thread_fence_rel();
        *seqcp += SEQC_MOD;
        MPASS(!seqc_in_modify(*seqcp));
}

#endif  /* _KERNEL */
#endif  /* _SYS_SEQC_H_ */