/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2021 Vladimir Kondratyev <wulf@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 _LINUXKPI_LINUX_SEQLOCK_H__
#define	_LINUXKPI_LINUX_SEQLOCK_H__

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/cdefs.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/rwlock.h>
#include <sys/seqc.h>

struct lock_class_key;

struct seqcount {
	seqc_t		seqc;
};
typedef struct seqcount seqcount_t;

struct seqlock {
	struct mtx	seql_lock;
	struct seqcount	seql_count;
};
typedef struct seqlock seqlock_t;

struct seqcount_mutex {
	seqc_t		seqc;
};
typedef struct seqcount_mutex seqcount_mutex_t;
typedef struct seqcount_mutex seqcount_ww_mutex_t;

static inline void
__seqcount_init(struct seqcount *seqcount, const char *name __unused,
    struct lock_class_key *key __unused)
{
	seqcount->seqc = 0;
}
#define	seqcount_init(seqcount)	__seqcount_init(seqcount, NULL, NULL)

static inline void
seqcount_mutex_init(struct seqcount_mutex *seqcount, void *mutex __unused)
{
	seqcount->seqc = 0;
}

#define	seqcount_ww_mutex_init(seqcount, ww_mutex) \
    seqcount_mutex_init((seqcount), (ww_mutex))

#define	write_seqcount_begin(s)						\
    _Generic(*(s),							\
	struct seqcount:	seqc_sleepable_write_begin,		\
	struct seqcount_mutex:	seqc_write_begin			\
    )(&(s)->seqc)

#define	write_seqcount_end(s)						\
    _Generic(*(s),							\
	struct seqcount:	seqc_sleepable_write_end,		\
	struct seqcount_mutex:	seqc_write_end				\
    )(&(s)->seqc)

static inline void
lkpi_write_seqcount_invalidate(seqc_t *seqcp)
{
	atomic_thread_fence_rel();
	*seqcp += SEQC_MOD * 2;
}
#define	write_seqcount_invalidate(s) lkpi_write_seqcount_invalidate(&(s)->seqc)

#define	read_seqcount_begin(s)	seqc_read(&(s)->seqc)
#define	raw_read_seqcount(s)	seqc_read_any(&(s)->seqc)

static inline seqc_t
lkpi_seqprop_sequence(const seqc_t *seqcp)
{
	return (atomic_load_int(__DECONST(seqc_t *, seqcp)));
}
#define	seqprop_sequence(s)	lkpi_seqprop_sequence(&(s)->seqc)

/*
 * XXX: Are predicts from inline functions still not honored by clang?
 */
#define	__read_seqcount_retry(seqcount, gen)	\
	(!seqc_consistent_no_fence(&(seqcount)->seqc, gen))
#define	read_seqcount_retry(seqcount, gen)	\
	(!seqc_consistent(&(seqcount)->seqc, gen))

static inline void
seqlock_init(struct seqlock *seqlock)
{
	/*
	 * Don't enroll to witness(4) to avoid orphaned references after struct
	 * seqlock has been freed. There is no seqlock destructor exists so we
	 * can't expect automatic mtx_destroy() execution before free().
	 */
	mtx_init(&seqlock->seql_lock, "seqlock", NULL, MTX_DEF|MTX_NOWITNESS);
	seqcount_init(&seqlock->seql_count);
}

static inline void
lkpi_write_seqlock(struct seqlock *seqlock, const bool irqsave)
{
	mtx_lock(&seqlock->seql_lock);
	if (irqsave)
		critical_enter();
	write_seqcount_begin(&seqlock->seql_count);
}

static inline void
write_seqlock(struct seqlock *seqlock)
{
	lkpi_write_seqlock(seqlock, false);
}

static inline void
lkpi_write_sequnlock(struct seqlock *seqlock, const bool irqsave)
{
	write_seqcount_end(&seqlock->seql_count);
	if (irqsave)
		critical_exit();
	mtx_unlock(&seqlock->seql_lock);
}

static inline void
write_sequnlock(struct seqlock *seqlock)
{
	lkpi_write_sequnlock(seqlock, false);
}

/*
 * Disable preemption when the consumer wants to disable interrupts.  This
 * ensures that the caller won't be starved if it is preempted by a
 * higher-priority reader, but assumes that the caller won't perform any
 * blocking operations while holding the write lock; probably a safe
 * assumption.
 */
#define	write_seqlock_irqsave(seqlock, flags)	do {	\
	(flags) = 0;					\
	lkpi_write_seqlock(seqlock, true);		\
} while (0)

static inline void
write_sequnlock_irqrestore(struct seqlock *seqlock,
    unsigned long flags __unused)
{
	lkpi_write_sequnlock(seqlock, true);
}

static inline unsigned
read_seqbegin(const struct seqlock *seqlock)
{
	return (read_seqcount_begin(&seqlock->seql_count));
}

#define	read_seqretry(seqlock, gen)	\
	read_seqcount_retry(&(seqlock)->seql_count, gen)

#endif	/* _LINUXKPI_LINUX_SEQLOCK_H__ */