/*      $NetBSD: subr_fault.c,v 1.4 2026/01/04 03:18:01 riastradh Exp $ */

/*
 * Copyright (c) 2020 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Maxime Villard.
 *
 * 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_fault.c,v 1.4 2026/01/04 03:18:01 riastradh Exp $");

#include <sys/param.h>
#include <sys/types.h>

#include <sys/atomic.h>
#include <sys/conf.h>
#include <sys/fault.h>
#include <sys/ioccom.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/lwp.h>
#include <sys/module.h>
#include <sys/sdt.h>
#include <sys/specificdata.h>
#include <sys/systm.h>
#include <sys/types.h>

typedef struct {
        volatile bool enabled;
        volatile bool oneshot;
        volatile unsigned long nth;
        volatile unsigned long cnt;
        volatile unsigned long nfaults;
} fault_t;

static fault_t fault_global __cacheline_aligned = {
        .enabled = false,
        .oneshot = false,
        .nth = FAULT_NTH_MIN,
        .cnt = 0,
        .nfaults = 0
};

static kmutex_t fault_global_lock __cacheline_aligned;
static specificdata_key_t fault_lwp_key;

/* -------------------------------------------------------------------------- */

bool
fault_inject(void)
{
        volatile unsigned long cnt;
        fault_t *f;

        if (__predict_false(cold))
                return false;

        if (__predict_false(atomic_load_acquire(&fault_global.enabled))) {
                f = &fault_global;
        } else {
                f = lwp_getspecific(fault_lwp_key);
                if (__predict_true(f == NULL))
                        return false;
                if (__predict_false(!f->enabled))
                        return false;
        }

        if (atomic_load_relaxed(&f->oneshot)) {
                if (__predict_true(atomic_load_relaxed(&f->nfaults) > 0))
                        return false;
        }

        cnt = atomic_inc_ulong_nv(&f->cnt);
        if (__predict_false(cnt % atomic_load_relaxed(&f->nth) == 0)) {
                atomic_inc_ulong(&f->nfaults);
                return true;
        }

        return false;
}

/* -------------------------------------------------------------------------- */

static int
fault_open(dev_t dev, int flag, int mode, struct lwp *l)
{
        return 0;
}

static int
fault_close(dev_t dev, int flag, int mode, struct lwp *l)
{
        return 0;
}

static int
fault_ioc_enable(struct fault_ioc_enable *args)
{
        fault_t *f;

        if (args->mode != FAULT_MODE_NTH_ONESHOT)
                return SET_ERROR(EINVAL);
        if (args->nth < FAULT_NTH_MIN)
                return SET_ERROR(EINVAL);

        switch (args->scope) {
        case FAULT_SCOPE_GLOBAL:
                mutex_enter(&fault_global_lock);
                if (fault_global.enabled) {
                        mutex_exit(&fault_global_lock);
                        return SET_ERROR(EEXIST);
                }
                fault_global.oneshot = true;
                atomic_store_relaxed(&fault_global.nth, args->nth);
                fault_global.cnt = 0;
                fault_global.nfaults = 0;
                atomic_store_release(&fault_global.enabled, true);
                mutex_exit(&fault_global_lock);
                break;
        case FAULT_SCOPE_LWP:
                f = lwp_getspecific(fault_lwp_key);
                if (f != NULL) {
                        if (f->enabled)
                                return SET_ERROR(EEXIST);
                } else {
                        f = kmem_zalloc(sizeof(*f), KM_SLEEP);
                        lwp_setspecific(fault_lwp_key, f);
                }
                f->oneshot = true;
                atomic_store_relaxed(&f->nth, args->nth);
                f->cnt = 0;
                f->nfaults = 0;
                atomic_store_release(&f->enabled, true);
                break;
        default:
                return SET_ERROR(EINVAL);
        }

        return 0;
}

static int
fault_ioc_disable(struct fault_ioc_disable *args)
{
        fault_t *f;

        switch (args->scope) {
        case FAULT_SCOPE_GLOBAL:
                mutex_enter(&fault_global_lock);
                if (!fault_global.enabled) {
                        mutex_exit(&fault_global_lock);
                        return SET_ERROR(ENOENT);
                }
                atomic_store_release(&fault_global.enabled, false);
                mutex_exit(&fault_global_lock);
                break;
        case FAULT_SCOPE_LWP:
                f = lwp_getspecific(fault_lwp_key);
                if (f == NULL)
                        return SET_ERROR(ENOENT);
                if (!f->enabled)
                        return SET_ERROR(ENOENT);
                atomic_store_release(&f->enabled, false);
                break;
        default:
                return SET_ERROR(EINVAL);
        }

        return 0;
}

static int
fault_ioc_getinfo(struct fault_ioc_getinfo *args)
{
        fault_t *f;

        switch (args->scope) {
        case FAULT_SCOPE_GLOBAL:
                args->nfaults = atomic_load_relaxed(&fault_global.nfaults);
                break;
        case FAULT_SCOPE_LWP:
                f = lwp_getspecific(fault_lwp_key);
                if (f == NULL)
                        return SET_ERROR(ENOENT);
                args->nfaults = atomic_load_relaxed(&f->nfaults);
                break;
        default:
                return SET_ERROR(EINVAL);
        }

        return 0;
}

static int
fault_ioctl(dev_t dev, u_long cmd, void *addr, int flag, struct lwp *l)
{
        switch (cmd) {
        case FAULT_IOC_ENABLE:
                return fault_ioc_enable(addr);
        case FAULT_IOC_DISABLE:
                return fault_ioc_disable(addr);
        case FAULT_IOC_GETINFO:
                return fault_ioc_getinfo(addr);
        default:
                return SET_ERROR(EINVAL);
        }
}

const struct cdevsw fault_cdevsw = {
        .d_open = fault_open,
        .d_close = fault_close,
        .d_read = noread,
        .d_write = nowrite,
        .d_ioctl = fault_ioctl,
        .d_stop = nostop,
        .d_tty = notty,
        .d_poll = nopoll,
        .d_mmap = nommap,
        .d_kqfilter = nokqfilter,
        .d_discard = nodiscard,
        .d_flag = D_OTHER | D_MPSAFE
};

/* -------------------------------------------------------------------------- */

MODULE(MODULE_CLASS_MISC, fault, NULL);

static void
fault_lwp_free(void *arg)
{
        fault_t *f = (fault_t *)arg;

        if (f == NULL) {
                return;
        }

        kmem_free(f, sizeof(*f));
}

static void
fault_init(void)
{
        mutex_init(&fault_global_lock, MUTEX_DEFAULT, IPL_NONE);
        lwp_specific_key_create(&fault_lwp_key, fault_lwp_free);
}

static int
fault_modcmd(modcmd_t cmd, void *arg)
{
        switch (cmd) {
        case MODULE_CMD_INIT:
                fault_init();
                return 0;
        case MODULE_CMD_FINI:
                return SET_ERROR(EINVAL);
        default:
                return SET_ERROR(ENOTTY);
        }
}