/*      $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;
        } 
}