/*      $NetBSD: pollpal.c,v 1.4 2022/03/28 12:33:22 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: pollpal.c,v 1.4 2022/03/28 12:33:22 riastradh Exp $");

#include <sys/module.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/lwp.h>

#include <sys/condvar.h>
#include <sys/conf.h>
#include <sys/device.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/mutex.h>
#include <sys/kmem.h>
#include <sys/poll.h>
#include <sys/select.h>

/*
* Create a device /dev/pollpal
*
* To use this device you need to do:
*      mknod /dev/pollpal c 351 0
*
*/

dev_type_open(pollpal_open);

static struct cdevsw pollpal_cdevsw = {
       .d_open = pollpal_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      pollpal_nopen = 0;

static int      pollpal_close(file_t *);
static int      pollpal_write(file_t *, off_t *, struct uio *, kauth_cred_t,
   int);
static int      pollpal_read(file_t *, off_t *, struct uio *, kauth_cred_t,
   int);
static int      pollpal_poll(file_t *, int);

const struct fileops pollpal_fileops = {
       .fo_read = pollpal_read,
       .fo_write = pollpal_write,
       .fo_ioctl = fbadop_ioctl,
       .fo_fcntl = fnullop_fcntl,
       .fo_poll = pollpal_poll,
       .fo_stat = fbadop_stat,
       .fo_close = pollpal_close,
       .fo_kqfilter = fnullop_kqfilter,
       .fo_restart = fnullop_restart,
};

typedef struct pollpal_softc {
       kmutex_t lock;
       kcondvar_t sc_cv;
       struct selinfo psel;
       char *buf;
       size_t buf_len;
       /* Device can have two states 1.READ_WAITING, 2.WRITE_WAITING. */
       enum states {
               READ_WAITING = 0,
               WRITE_WAITING = 1
       } sc_state;
} pal_t;

static int
check_pal(const char *str, size_t len)
{
       size_t n;

       n = 0;

       while (n <= len / 2) {
               if (str[n] != str[len - n - 1])
                       return 0;

               n++;
       }

       return 1;
}

int
pollpal_open(dev_t dev, int flag, int mode, struct lwp *l __unused)
{
       struct file *fp;
       int error, fd;
       pal_t *pl;

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

       ++pollpal_nopen;

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

       pl->sc_state = READ_WAITING;
       mutex_init(&pl->lock, MUTEX_DEFAULT, IPL_NONE);
       cv_init(&pl->sc_cv, "sc_cv");
       selinit(&pl->psel);

       return fd_clone(fp, fd, flag, &pollpal_fileops, pl);
}

int
pollpal_close(file_t * fp)
{
       pal_t * pl = fp->f_data;
       KASSERT(pl != NULL);

       if (pl->buf != NULL)
               kmem_free(pl->buf, pl->buf_len);

       seldestroy(&pl->psel);
       cv_destroy(&pl->sc_cv);
       mutex_destroy(&pl->lock);
       kmem_free(pl, sizeof(*pl));

       --pollpal_nopen;

       return 0;
}

/*
* Device would write only in READ_WAITING state and then update the state to
* WRITE_WAITING.
*/
int
pollpal_write(file_t *fp, off_t *offset, struct uio *uio, kauth_cred_t cred,
   int flag)
{
       pal_t *pl = fp->f_data;
       int error;

       error = 0;

       /* To ensure that only single process can write in device at a time. */
       mutex_enter(&pl->lock);
       cv_broadcast(&pl->sc_cv);
       switch (pl->sc_state) {
       case READ_WAITING:
               pl->sc_state = WRITE_WAITING;
               selnotify(&pl->psel, POLLOUT | POLLWRNORM, 0);
               while (pl->sc_state == WRITE_WAITING) {
                       if (pl->buf) {
                               error = cv_wait_sig(&pl->sc_cv, &pl->lock);
                               if (error)
                                       goto ret;

                       }

                       pl->buf_len = uio->uio_iov->iov_len;
                       pl->buf = kmem_alloc(pl->buf_len, KM_SLEEP);
                       uiomove(pl->buf, pl->buf_len, uio);
                       printf("Use cat to know the result.\n");
                       break;
               }
               break;
       case WRITE_WAITING:
               printf("State: WRITE_WAITING\n");
               break;
       }

ret:
       mutex_exit(&pl->lock);
       return error;
}

/*
* Device would read only in WRITE_WAITING state and then update the state to
* READ_WAITING.
*/
int
pollpal_read(file_t *fp, off_t *offset, struct uio *uio, kauth_cred_t cred,
   int flags)
{
       pal_t *pl = fp->f_data;
       int error;

       error = 0;

       /* To ensure that only single process can read device at a time. */
       mutex_enter(&pl->lock);
       cv_broadcast(&pl->sc_cv);
       switch (pl->sc_state) {
       case READ_WAITING:
               printf("State: READ_WAITING\n");
               printf("You need to write something to the module first!\n");
               goto ret;
       case WRITE_WAITING:
               pl->sc_state = READ_WAITING;
               selnotify(&pl->psel, POLLIN | POLLRDNORM, 0);
               while (pl->sc_state == READ_WAITING) {
                       if (!pl->buf) {
                               error = cv_wait_sig(&pl->sc_cv, &pl->lock);
                               if (error)
                                       goto ret;

                       }
                       printf("The string you entered was: ");
                       uiomove(pl->buf, pl->buf_len, uio);
                       printf("\n");
                       if (check_pal(pl->buf, pl->buf_len))
                               printf("String '%s' was a palindrome.\n",
                                   pl->buf);
                       else
                               printf("String '%s' was not a palindrome.\n",
                                   pl->buf);

                       break;
               }
               break;
       }
       kmem_free(pl->buf, pl->buf_len);
       pl->buf = NULL;

ret:
       mutex_exit(&pl->lock);
       return error;
}

int
pollpal_poll(struct file *fp, int events)
{
       pal_t *pl = fp->f_data;
       int revents;

       revents = 0;

       mutex_enter(&pl->lock);
       switch (pl->sc_state) {
       case READ_WAITING:
               if (events & (POLLOUT | POLLWRNORM)) {
                       /* When device is in READ_WAITING state it can write */
                       revents |= POLLOUT | POLLWRNORM;
               } else {
                       /* Record the request if it wasn't satisfied. */
                       selrecord(curlwp, &pl->psel);
               }
               break;
       case WRITE_WAITING:
               if (events & (POLLIN | POLLRDNORM)) {
                       /* When device is in WRITE_WAITING state it can read. */
                       revents |= POLLIN | POLLRDNORM;
               } else {
                       /* Record the request if it wasn't satisfied. */
                       selrecord(curlwp, &pl->psel);
               }
               break;
       }

       mutex_exit(&pl->lock);
       return revents;
}

MODULE(MODULE_CLASS_MISC, pollpal, NULL);

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

       switch (cmd) {
       case MODULE_CMD_INIT:
               if (devsw_attach("pollpal", NULL, &bmajor, &pollpal_cdevsw,
                   &cmajor))
                       return ENXIO;
               return 0;
       case MODULE_CMD_FINI:
               if (pollpal_nopen != 0)
                       return EBUSY;
               devsw_detach(NULL, &pollpal_cdevsw);
               return 0;
       default:
               return ENOTTY;
       }
}

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