/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2000 Mark R. V. Murray & Jeroen C. van Gelderen
 * Copyright (c) 2001-2004 Mark R. V. Murray
 * Copyright (c) 2014 Eitan Adler
 * Copyright (c) 2025 Pietro Cerutti
 * All rights reserved.
 *
 * 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
 *    in this position and unchanged.
 * 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 AUTHORS ``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 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/param.h>
#include <sys/systm.h>
#include <sys/conf.h>
#include <sys/uio.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/disk.h>
#include <sys/bus.h>
#include <sys/filio.h>
#include <sys/event.h>

#include <machine/bus.h>
#include <machine/vmparam.h>

/* For use with destroy_dev(9). */
static struct cdev *full_dev;
static struct cdev *null_dev;
static struct cdev *zero_dev;

static d_write_t full_write;
static d_write_t null_write;
static d_ioctl_t null_ioctl;
static d_ioctl_t zero_ioctl;
static d_read_t zero_read;
static d_kqfilter_t kqfilter;
static int one_ev(struct knote *kn, long hint);
static int zero_ev(struct knote *kn, long hint);

static const struct filterops one_fop = {
        .f_isfd =       1,
        .f_event =      one_ev,
        .f_copy =       knote_triv_copy,
};

static const struct filterops zero_fop = {
        .f_isfd =       1,
        .f_event =      zero_ev,
        .f_copy =       knote_triv_copy,
};

static struct cdevsw full_cdevsw = {
        .d_version =    D_VERSION,
        .d_read =       zero_read,
        .d_write =      full_write,
        .d_ioctl =      zero_ioctl,
        .d_kqfilter =   kqfilter,
        .d_name =       "full",
};

static struct cdevsw null_cdevsw = {
        .d_version =    D_VERSION,
        .d_read =       (d_read_t *)nullop,
        .d_write =      null_write,
        .d_ioctl =      null_ioctl,
        .d_kqfilter =   kqfilter,
        .d_name =       "null",
};

static struct cdevsw zero_cdevsw = {
        .d_version =    D_VERSION,
        .d_read =       zero_read,
        .d_write =      null_write,
        .d_ioctl =      zero_ioctl,
        .d_kqfilter =   kqfilter,
        .d_name =       "zero",
        .d_flags =      D_MMAP_ANON,
};

/* ARGSUSED */
static int
full_write(struct cdev *dev __unused, struct uio *uio __unused, int flags __unused)
{

        return (ENOSPC);
}

/* ARGSUSED */
static int
null_write(struct cdev *dev __unused, struct uio *uio, int flags __unused)
{
        uio->uio_resid = 0;

        return (0);
}

/* ARGSUSED */
static int
null_ioctl(struct cdev *dev __unused, u_long cmd, caddr_t data __unused,
    int flags __unused, struct thread *td)
{
        struct diocskerneldump_arg kda;
        int error;

        error = 0;
        switch (cmd) {
        case DIOCSKERNELDUMP:
                bzero(&kda, sizeof(kda));
                kda.kda_index = KDA_REMOVE_ALL;
                error = dumper_remove(NULL, &kda);
                break;
        case FIONBIO:
                break;
        case FIOASYNC:
                if (*(int *)data != 0)
                        error = EINVAL;
                break;
        default:
                error = ENOIOCTL;
        }
        return (error);
}

/* ARGSUSED */
static int
zero_ioctl(struct cdev *dev __unused, u_long cmd, caddr_t data __unused,
           int flags __unused, struct thread *td)
{
        int error;
        error = 0;

        switch (cmd) {
        case FIONBIO:
                break;
        case FIOASYNC:
                if (*(int *)data != 0)
                        error = EINVAL;
                break;
        default:
                error = ENOIOCTL;
        }
        return (error);
}

/* ARGSUSED */
static int
zero_read(struct cdev *dev __unused, struct uio *uio, int flags __unused)
{
        void *zbuf;
        ssize_t len;
        int error = 0;

        KASSERT(uio->uio_rw == UIO_READ,
            ("Can't be in %s for write", __func__));
        zbuf = __DECONST(void *, zero_region);
        while (uio->uio_resid > 0 && error == 0) {
                len = uio->uio_resid;
                if (len > ZERO_REGION_SIZE)
                        len = ZERO_REGION_SIZE;
                error = uiomove(zbuf, len, uio);
        }

        return (error);
}

/* ARGSUSED */
static int
null_modevent(module_t mod __unused, int type, void *data __unused)
{
        switch(type) {
        case MOD_LOAD:
                if (bootverbose)
                        printf("null: <full device, null device, zero device>\n");
                full_dev = make_dev_credf(MAKEDEV_ETERNAL_KLD, &full_cdevsw, 0,
                    NULL, UID_ROOT, GID_WHEEL, 0666, "full");
                null_dev = make_dev_credf(MAKEDEV_ETERNAL_KLD, &null_cdevsw, 0,
                    NULL, UID_ROOT, GID_WHEEL, 0666, "null");
                zero_dev = make_dev_credf(MAKEDEV_ETERNAL_KLD, &zero_cdevsw, 0,
                    NULL, UID_ROOT, GID_WHEEL, 0666, "zero");
                break;

        case MOD_UNLOAD:
                destroy_dev(full_dev);
                destroy_dev(null_dev);
                destroy_dev(zero_dev);
                break;

        case MOD_SHUTDOWN:
                break;

        default:
                return (EOPNOTSUPP);
        }

        return (0);
}

static int
one_ev(struct knote *kn, long hint)
{

        return (1);
}

static int
zero_ev(struct knote *kn, long hint)
{

        return (0);
}

static int
kqfilter(struct cdev *dev, struct knote *kn)
{

        switch (kn->kn_filter) {
        case EVFILT_READ:
            kn->kn_fop = dev->si_devsw == &null_cdevsw ? &zero_fop : &one_fop;
            return (0);
        case EVFILT_WRITE:
            kn->kn_fop = dev->si_devsw == &full_cdevsw ? &zero_fop : &one_fop;
            return (0);
        default:
            return (EOPNOTSUPP);
        }
}

DEV_MODULE(null, null_modevent, NULL);
MODULE_VERSION(null, 1);