/*      $NetBSD: fopsmapper.c,v 1.3 2024/04/17 18:10:27 riastradh Exp $ */

/*-
 * Copyright (c) 2020 The NetBSD Foundation, Inc.
 * 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.
 * 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: fopsmapper.c,v 1.3 2024/04/17 18:10:27 riastradh Exp $");

#include <sys/types.h>

#include <sys/conf.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/mman.h>
#include <sys/module.h>
#include <sys/mutex.h>
#include <sys/param.h>
#include <sys/systm.h>

#include <uvm/uvm_extern.h>

/*
 * To use this module you need to:
 *
 * mknod /dev/fopsmapper c 351 0
 */

dev_open_t fopsmapper_open;

const struct cdevsw fopsmapper_cdevsw = {
        .d_open = fopsmapper_open,
        .d_close = noclose,
        .d_read = noread,
        .d_write = nowrite,
        .d_ioctl = noioctl,
        .d_stop = nostop,
        .d_tty = notty,
        .d_poll = nopoll,
        .d_mmap = nommap,
        .d_kqfilter = nokqfilter,
        .d_discard = nodiscard,
        .d_flag = D_OTHER
};

static int fopsmapper_mmap(struct file *, off_t *, size_t, int, int *, int *,
    struct uvm_object **, int *);
static int fopsmapper_close(struct file *);

const struct fileops mapper_fileops = {
        .fo_read = fbadop_read,
        .fo_write = fbadop_write,
        .fo_ioctl = fbadop_ioctl,
        .fo_fcntl = fnullop_fcntl,
        .fo_poll = fnullop_poll,
        .fo_stat = fbadop_stat,
        .fo_close = fopsmapper_close,
        .fo_kqfilter = fnullop_kqfilter,
        .fo_restart = fnullop_restart,
        .fo_mmap = fopsmapper_mmap,
};

struct fopsmapper_softc {
        char *buf;
        struct uvm_object *uobj;
        size_t bufsize;
};

int
fopsmapper_open(dev_t dev, int flag, int mode, struct lwp *l)
{
        struct fopsmapper_softc *fo;
        struct file *fp;
        int fd, error;

        if ((error = fd_allocfile(&fp, &fd)) != 0)
                return error;

        fo = kmem_zalloc(sizeof(*fo), KM_SLEEP);

        return fd_clone(fp, fd, flag, &mapper_fileops, fo);
}

int
fopsmapper_mmap(struct file *fp, off_t *offp, size_t size, int prot,
    int *flagsp, int *advicep, struct uvm_object **uobjp, int *maxprotp)
{
        struct fopsmapper_softc *fo;
        vaddr_t va;
        int error;

        if (prot & PROT_EXEC)
                return EACCES;

        if (size != (size_t)PAGE_SIZE)
                return EINVAL;

        if ((fo = fp->f_data) == NULL)
                return ENXIO;

        fo->bufsize = size;
        fo->uobj = uao_create(size, 0);

        fo->buf = NULL;

        /*
         * Map the uvm object into kernel.  Consumes our reference to
         * uobj on success.
         */
        error = uvm_map(kernel_map, &va, fo->bufsize, fo->uobj, 0, 0,
            UVM_MAPFLAG(UVM_PROT_RW, UVM_PROT_RW,
                UVM_INH_SHARE, UVM_ADV_RANDOM, 0));
        if (error) {
                uao_detach(fo->uobj);
                goto out;
        }
        fo->buf = (char *)va;
        snprintf(fo->buf, 13, "Hey There!");

        /* Get the reference of uobj */
        uao_reference(fo->uobj);
        *uobjp = fo->uobj;
        *maxprotp = prot;
        *advicep = UVM_ADV_RANDOM;
        error = 0;

out:    return error;
}

int
fopsmapper_close(struct file *fp)
{
        struct fopsmapper_softc *fo;

        fo = fp->f_data;
        KASSERT(fo != NULL);

        if (fo->buf != NULL)
                uvm_deallocate(kernel_map, (vaddr_t)fo->buf, fo->bufsize);

        kmem_free(fo, sizeof(*fo));

        return 0;
}

MODULE(MODULE_CLASS_MISC, fopsmapper, NULL);

static int
fopsmapper_modcmd(modcmd_t cmd, void *arg __unused)
{
        int cmajor = 351, bmajor = -1;

        switch (cmd) {
        case MODULE_CMD_INIT:
                if (devsw_attach("fopsmapper", NULL, &bmajor,
                        &fopsmapper_cdevsw, &cmajor))
                        return ENXIO;
                return 0;
        case MODULE_CMD_FINI:
                return EBUSY;
        default:
                return ENOTTY;
        }
}