ttynvt/ttynvt.c

/*
 * Copyright (c) 2018 Lars Thrane A/S
 * SPDX-License-Identifier: GPL-2.0
 */
#include "config.h"

#include <cuse_lowlevel.h>
#include <errno.h>
#include <fuse_opt.h>
#include <netdb.h>
#include <pthread.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <termios.h>
#include <unistd.h>
#include <linux/sockios.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/types.h>

#include "telnet.h"

#define RX_BUF_SIZE 1024


static struct ttynvt_param {
    unsigned int    major;
    unsigned int    minor;
    const char     *dev_name;
    char           *host;
    unsigned int    port;
    unsigned int    debug;
} ttynvt_param;

typedef struct ttynvt {
    int             nonblock;
    pthread_mutex_t tty_lock;
    pthread_mutex_t poll_lock;
    pthread_t       thread_id;

    pthread_cond_t  cond;

    struct fuse_pollhandle *ph;

    struct pollfd   fds[1];

    struct termios  tio;
    unsigned char   mcr;

    char            buf[RX_BUF_SIZE];
    size_t          blen;
    size_t          rxcnt;

    int             txbuf_size;
    int             epipe;
    volatile sig_atomic_t error;

    tn_ctx_t       *tn;
} ttynvt_t;

static void _log(int prio, const char *fmt, ...)
{
    va_list         arg;

    if (prio >= LOG_DEBUG && ttynvt_param.debug <= 0)
        return;

    va_start(arg, fmt);
    vsyslog(prio, fmt, arg);
    va_end(arg);
}

static void ttynvt_release(fuse_req_t req, struct fuse_file_info *info)
{
    ttynvt_t       *tty = (ttynvt_t *) (uintptr_t) info->fh;

    _log(LOG_INFO, "connection closed\n");

    close(tty->fds[0].fd);

    (void)pthread_cancel(tty->thread_id);
    (void)pthread_join(tty->thread_id, NULL);
    (void)pthread_mutex_destroy(&tty->tty_lock);
    (void)pthread_mutex_destroy(&tty->poll_lock);
    (void)pthread_cond_destroy(&tty->cond);

    if (tty->ph)
        fuse_pollhandle_destroy(tty->ph);

    free(tty->tn);
    free(tty);
    fuse_reply_err(req, 0);
}

static void _notify(ttynvt_t * tty)
{
    pthread_mutex_lock(&tty->poll_lock);
    if (tty->ph)
    {
        fuse_lowlevel_notify_poll(tty->ph);
        fuse_pollhandle_destroy(tty->ph);
        tty->ph = NULL;
    }
    pthread_mutex_unlock(&tty->poll_lock);
    pthread_cond_signal(&tty->cond);
}

static void _update_notify(ttynvt_t * tty, struct fuse_pollhandle *ph)
{
    pthread_mutex_lock(&tty->poll_lock);
    struct fuse_pollhandle *tmp_ph = tty->ph;

    tty->ph = ph;
    pthread_mutex_unlock(&tty->poll_lock);
    if (tmp_ph)
        fuse_pollhandle_destroy(tmp_ph);
}

static unsigned int _write_avail(ttynvt_t * tty)
{
    size_t          write_avail;
    int             used;

    pthread_mutex_lock(&tty->tty_lock);
    if (ioctl(tty->fds[0].fd, SIOCOUTQ, &used) < 0)
        return 0;

    write_avail = tty->txbuf_size - used;

    pthread_mutex_unlock(&tty->tty_lock);
    return write_avail;
}

static int _read_avail(ttynvt_t * tty)
{
    int             read_avail;

    pthread_mutex_lock(&tty->tty_lock);

    read_avail = tty->rxcnt;

    pthread_mutex_unlock(&tty->tty_lock);
    return read_avail;
}

static void    *_read_net(void *arg)
{
    ttynvt_t       *tty = (ttynvt_t *) arg;
    ssize_t         res;
    int             tn_res = -1;

    pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);

    while (1)
    {
        res = poll(tty->fds, 1, -1);
        if (res < 0)
        {
            if (errno == EINTR)
                continue;
            else
                break;
        }
        else if (tty->fds[0].revents & (POLLERR | POLLHUP | POLLNVAL))
        {
            break;
        }
        else if (tty->fds[0].revents & POLLIN)
        {
            pthread_mutex_lock(&tty->tty_lock);
            int             read_avail = RX_BUF_SIZE - tty->blen;

            if (read_avail == 0)
            {
                /*buffer overflow */
                tty->blen = 0;
                read_avail = RX_BUF_SIZE;
                _log(LOG_WARNING, "Rx buffer overflow\n");
            }
            res = read(tty->fds[0].fd, tty->buf + tty->blen, read_avail);
            if (res <= 0)
            {
                pthread_mutex_unlock(&tty->tty_lock);
                break;
            }
            else
            {
                tty->blen += res;

                tn_res = telnet_rx(tty->tn, tty->buf, &tty->blen);
                if (tn_res == 0)
                {
                    tty->rxcnt = tty->blen;
                    _notify(tty);
                }
                pthread_mutex_unlock(&tty->tty_lock);
            }
        }
    }

    if (res == 0)
        _log(LOG_INFO, "Connection closed by remote host\n");
    else
        _log(LOG_ERR, "Rx read error:%s\n", strerror(errno));

    tty->error = 1;
    _notify(tty);

    return 0;
}

static int _srv_connect(const char *host, unsigned int port)
{
    struct sockaddr_in serveraddr;
    struct hostent *server;
    int             sockfd, err;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        _log(LOG_ERR, "Socket open failed: %s\n", strerror(errno));
        return sockfd;
    }

    server = gethostbyname(host);
    if (server == NULL)
    {
        _log(LOG_ERR, "Cannot resolve host name: %s\n", strerror(errno));
        close(sockfd);
        return -1;
    }

    bzero((char *)&serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, (char *)&serveraddr.sin_addr.s_addr,
          server->h_length);
    serveraddr.sin_port = htons(port);

    err = connect(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));
    if (err < 0)
    {
        _log(LOG_ERR, "Failed to connect to: %s:%u:%s\n",
             host, port, strerror(errno));
        close(sockfd);
        return -1;
    }

    return sockfd;
}

static int _srv_write(void *cctx, const void *buf, int len)
{
    ttynvt_t       *tty = cctx;
    int             res;

    res = write(tty->fds[0].fd, buf, len);

    return res;
}

static int _srv_read(void *cctx, int timeout)
{
    ttynvt_t       *tty = cctx;
    int             res;

    while (1)
    {
        res = poll(tty->fds, 1, timeout);
        if (res <= 0)
            return res;

        if (tty->fds[0].revents & POLLIN)
        {
            res = read(tty->fds[0].fd, tty->buf + tty->blen,
                       RX_BUF_SIZE - tty->blen);
            if (res <= 0)
                return res;
            tty->blen += (size_t) res;
            res = telnet_rx(tty->tn, tty->buf, &tty->blen);
            if (res == 0)
            {
                tty->rxcnt = tty->blen;
                break;
            }
        }
    }
    return 1;
}

static void _modem_status_cb(void *cctx, int status)
{
    ttynvt_t       *tty = cctx;

    tty->mcr &= ~(TIOCM_CD | TIOCM_RI | TIOCM_CTS | TIOCM_DSR);

    _log(LOG_INFO, "Modem status: 0x%02x\n", status);

    if (status & TNS_STATE_CD)
        tty->mcr |= TIOCM_CD;
    if (status & TNS_STATE_RI)
        tty->mcr |= TIOCM_RI;
    if (status & TNS_STATE_CTS)
        tty->mcr |= TIOCM_CTS;
    if (status & TNS_STATE_DSR)
        tty->mcr |= TIOCM_DSR;
}

static void ttynvt_open(fuse_req_t req, struct fuse_file_info *info)
{
    ttynvt_t       *tty;
    socklen_t       len;
    int             sockfd;
    int             res;

    tty = calloc(1, sizeof(*tty));
    if (!tty)
    {
        fuse_reply_err(req, ENOMEM);
        return;
    }

    tty->tn = telnet_ctx_init(tty, _srv_write, _srv_read, _modem_status_cb);
    if (!tty->tn)
    {
        free(tty);
        fuse_reply_err(req, ENOMEM);
        return;
    }

    sockfd = _srv_connect(ttynvt_param.host, ttynvt_param.port);
    if (sockfd < 0)
    {
        free(tty->tn);
        free(tty);
        fuse_reply_err(req, EFAULT);
        return;
    }

    tty->fds[0].fd = sockfd;
    tty->fds[0].events = POLLIN;
    tty->blen = 0;
    tty->rxcnt = 0;

    res = telnet_open(tty->tn);
    if (res < 0)
    {
        free(tty->tn);
        free(tty);
        fuse_reply_err(req, EBADE);
        return;
    }

    len = sizeof(tty->txbuf_size);
    if (getsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &tty->txbuf_size, &len) < 0)
    {
        free(tty->tn);
        free(tty);
        fuse_reply_err(req, EIO);
        return;
    }

    if (pthread_mutex_init(&tty->tty_lock, NULL) < 0 ||
        pthread_mutex_init(&tty->poll_lock, NULL) < 0 ||
        pthread_cond_init(&tty->cond, NULL) < 0 ||
        pthread_create(&tty->thread_id, NULL, &_read_net, tty))
    {
        free(tty->tn);
        free(tty);
        fuse_reply_err(req, ENOMEM);
        return;
    }

    info->fh = (uintptr_t) tty;
    info->nonseekable = 1;
    info->direct_io = 1;

    _log(LOG_INFO, "Open connection to server: %s:%d\n",
         ttynvt_param.host, ttynvt_param.port);

    fuse_reply_open(req, info);
}

static void
ttynvt_read(fuse_req_t req, size_t size, off_t off,
            struct fuse_file_info *info)
{
    ttynvt_t       *tty = (ttynvt_t *) (uintptr_t) info->fh;

    if (tty->error)
    {
        if (tty->epipe == 0)
        {
            _log(LOG_WARNING, "Rx EPIPE\n");
            tty->epipe = 1;
            fuse_reply_buf(req, tty->buf, 0);
        }
        else
            fuse_reply_err(req, EBADFD);

        return;
    }

    pthread_mutex_lock(&tty->tty_lock);
    if (tty->rxcnt == 0 && !(info->flags & O_NONBLOCK))
    {
        pthread_cond_wait(&tty->cond, &tty->tty_lock);
    }
    if (size > tty->rxcnt)
        size = tty->rxcnt;
    if (size > 0)
    {
        fuse_reply_buf(req, tty->buf, size);
        memmove(tty->buf, tty->buf + size, tty->blen - size);
        tty->blen -= size;
        tty->rxcnt -= size;
    }
    else
    {
        fuse_reply_err(req, EINTR);
    }
    pthread_mutex_unlock(&tty->tty_lock);
}

static void
ttynvt_write(fuse_req_t req, const char *data, size_t size, off_t off,
             struct fuse_file_info *info)
{
    int             res;

    ttynvt_t       *tty = (ttynvt_t *) (uintptr_t) info->fh;

    if (size == 0)
    {
        fuse_reply_write(req, 0);
        return;
    }

    if (tty->error)
    {
        fuse_reply_err(req, EPIPE);
        return;
    }

    if (tty->nonblock || (info->flags & O_NONBLOCK))
    {
        size_t          write_avail = _write_avail(tty);

        if (size > write_avail)
            size = write_avail;
    }

    res = telnet_tx(tty->tn, data, size);
    if (res < 0)
    {
        tty->error = 1;
        fuse_reply_err(req, EPIPE);
        return;
    }
#if 0
    else if (res == 0)
    {
        fuse_reply_err(req, EAGAIN);
        return;
    }
#endif

    fuse_reply_write(req, size);
}

static int baudrate(speed_t speed)
{
    return speed == B50 ? 50 :
        speed == B75 ? 75 :
        speed == B110 ? 110 :
        speed == B300 ? 300 :
        speed == B600 ? 600 :
        speed == B1200 ? 1200 :
        speed == B1800 ? 1800 :
        speed == B2400 ? 2400 :
        speed == B4800 ? 4800 :
        speed == B9600 ? 9600 :
        speed == B19200 ? 19200 :
        speed == B38400 ? 38400 :
        speed == B57600 ? 57600 :
        speed == B115200 ? 115200 : speed == B230400 ? 230400 : 0;
}

static const char pstr[] = { ' ', 'N', 'O', 'E', 'M', 'S' };

static void
ttynvt_ioctl(fuse_req_t req, int cmd, void *arg,
             struct fuse_file_info *info, unsigned int flags,
             const void *in_buf, size_t in_bufsz, size_t out_bufsz)
{
    ttynvt_t       *tty = (ttynvt_t *) (uintptr_t) info->fh;
    unsigned int    tiocm = 0;
    static unsigned int mcr = 0;
    static struct termios tio = {
        .c_cflag = B115200 | CS8 | PARODD | CREAD | CLOCAL,
    };
    int             val;

    switch (cmd)
    {
    case TCSETSF:
    case TCSETSW:
    case TCSETS:
        if (!in_bufsz)
        {
            struct iovec    iov = { arg, sizeof(struct termios) };
            fuse_reply_ioctl_retry(req, &iov, 1, NULL, 0);
        }
        else
        {
            speed_t         speed;
            int             csize, par, sb;

            memcpy(&tio, in_buf, in_bufsz);

            speed = cfgetospeed(&tio);
            val = htonl(baudrate(speed));
            telnet_rfc2217_cfg(tty->tn, TNS_SET_BAUDRATE, &val, 4);

            if ((tio.c_cflag & CSIZE) == CS5)
                csize = 5;
            else if ((tio.c_cflag & CSIZE) == CS6)
                csize = 6;
            else if ((tio.c_cflag & CSIZE) == CS7)
                csize = 7;
            else
                csize = 8;
            telnet_rfc2217_cfg(tty->tn, TNS_SET_DATASIZE, &csize, 1);

            if (tio.c_cflag & PARENB && tio.c_iflag & IGNPAR)
                par = 1;
#ifdef CMSPAR
            else if (tio.c_cflag & PARENB && tio.c_iflag & CMSPAR)
            {
                if (tio.c_cflag & PARODD)
                    par = 4;
                else
                    par = 5;
            }
#endif
            else if (tio.c_cflag & PARENB)
                par = 3;
            else
                par = 1;
            telnet_rfc2217_cfg(tty->tn, TNS_SET_PARITY, &par, 1);

            if (tio.c_cflag & CSTOPB)
                sb = 2;
            else
                sb = 1;
            telnet_rfc2217_cfg(tty->tn, TNS_SET_STOPSIZE, &sb, 1);

            if (tio.c_cflag & CRTSCTS)
                telnet_rfc2217_ctl(tty->tn, TNS_CTL_CTSRTS);

            if (!(mcr & TIOCM_DTR) && speed != B0)
            {
                mcr |= TIOCM_DTR;
                telnet_rfc2217_ctl(tty->tn, TNS_CTL_DTR_ON);
            }

            _log(LOG_DEBUG,
                 "CFG ioctl: %u%c%u%u %cCTSRTS %cCREAD %cHUPCL %cCLOCAL\n",
                 baudrate(speed), pstr[par], csize, sb,
                 tio.c_cflag & CRTSCTS ? '+' : '-',
                 tio.c_cflag & CREAD ? '+' : '-',
                 tio.c_cflag & HUPCL ? '+' : '-',
                 tio.c_cflag & CLOCAL ? '+' : '-');

            fuse_reply_ioctl(req, 0, 0, 0);
        }
        break;
    case TCGETS:
        if (out_bufsz)
        {
            fuse_reply_ioctl(req, 0, &tio, sizeof(struct termio));
        }
        else
        {
            struct iovec    iov = { arg, sizeof(struct termio) };
            fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
        }
        break;

    case TIOCINQ:              /* Get the number of bytes in the input
                                 * buffer */
        if (out_bufsz)
        {
            size_t          rx_size = _read_avail(tty);

            fuse_reply_ioctl(req, 0, &rx_size, sizeof(size_t));
        }
        else
        {
            struct iovec    iov = { arg, sizeof(size_t) };
            fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
        }

        break;
    case TIOCOUTQ:             /* Get the number of bytes in the output
                                 * buffer */
        if (out_bufsz)
        {
            size_t          tx_size = _write_avail(tty);

            fuse_reply_ioctl(req, 0, &tx_size, sizeof(size_t));
        }
        else
        {
            struct iovec    iov = { arg, sizeof(size_t) };
            fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
        }
        break;
    case TCFLSH:
        if (arg == TCIFLUSH)
        {
            /*todo */
        }
        else if ((size_t) arg == TCOFLUSH)
        {
            /*todo */
        }
        else if ((size_t) arg == TCIOFLUSH)
        {
            /*todo */
        }
        fuse_reply_ioctl(req, 0, 0, 0);
        break;
    case TCIFLUSH:
        val = 1;
        telnet_rfc2217_cfg(tty->tn, TNS_SET_PURGE, &val, 1);
        pthread_mutex_lock(&tty->tty_lock);
        tty->blen = 0;
        pthread_mutex_unlock(&tty->tty_lock);

        fuse_reply_ioctl(req, 0, 0, 0);
        break;
    case TCOFLUSH:
        val = 2;
        telnet_rfc2217_cfg(tty->tn, TNS_SET_PURGE, &val, 1);
        fuse_reply_ioctl(req, 0, 0, 0);
        break;
    case TCIOFLUSH:
        val = 3;
        telnet_rfc2217_cfg(tty->tn, TNS_SET_PURGE, &val, 1);
        fuse_reply_ioctl(req, 0, 0, 0);
        break;
    case TIOCMGET:
        if (out_bufsz)
        {
            fuse_reply_ioctl(req, 0, &mcr, sizeof(unsigned int));
        }
        else
        {
            struct iovec    iov = { arg, sizeof(unsigned int) };
            fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
        }
        break;
    case TIOCMBIS:
        if (!in_bufsz)
        {
            struct iovec    iov = { arg, sizeof(unsigned int) };
            fuse_reply_ioctl_retry(req, &iov, 1, NULL, 0);
        }
        else
        {
            tiocm = *(unsigned int *)in_buf;
            fuse_reply_ioctl(req, 0, 0, 0);
        }
        if (tiocm & TIOCM_RTS)
        {
            mcr |= TIOCM_RTS;
            telnet_rfc2217_ctl(tty->tn, TNS_CTL_RTS_ON);
        }
        if (tiocm & TIOCM_DTR)
        {
            mcr |= TIOCM_DTR;
            telnet_rfc2217_ctl(tty->tn, TNS_CTL_DTR_ON);
        }
        break;
    case TIOCMBIC:
        if (!in_bufsz)
        {
            struct iovec    iov = { arg, sizeof(unsigned int) };
            fuse_reply_ioctl_retry(req, &iov, 1, NULL, 0);
        }
        else
        {
            tiocm = *(unsigned int *)in_buf;
            fuse_reply_ioctl(req, 0, 0, 0);
        }
        if (tiocm & TIOCM_RTS)
        {
            mcr &= ~TIOCM_RTS;
            telnet_rfc2217_ctl(tty->tn, TNS_CTL_RTS_OFF);
        }
        if (tiocm & TIOCM_DTR)
        {
            mcr &= ~TIOCM_DTR;
            telnet_rfc2217_ctl(tty->tn, TNS_CTL_DTR_OFF);
        }
        break;
    case TIOCMSET:
        if (!in_bufsz)
        {
            struct iovec    iov = { arg, sizeof(unsigned int) };
            fuse_reply_ioctl_retry(req, &iov, 1, NULL, 0);
        }
        else
        {
            tiocm = *(unsigned int *)in_buf;
            fuse_reply_ioctl(req, 0, 0, 0);

            _log(LOG_DEBUG, "CFG ioctl: DTR=%c RTS=%c\n",
                 tiocm & TIOCM_DTR ? '1' : '0', tiocm & TIOCM_RTS ? '1' : '0');

            mcr &= ~(TIOCM_RTS | TIOCM_DTR);
            mcr |= tiocm & (TIOCM_RTS | TIOCM_DTR);
            telnet_rfc2217_ctl(tty->tn, (tiocm & TIOCM_DTR) ?
                               TNS_CTL_DTR_ON : TNS_CTL_DTR_OFF);
            telnet_rfc2217_ctl(tty->tn, (tiocm & TIOCM_RTS) ?
                               TNS_CTL_RTS_ON : TNS_CTL_RTS_OFF);
        }
        break;
    case TCSBRK:
        fuse_reply_ioctl(req, 0, 0, 0);
        break;
    case TIOCGWINSZ:
        if (out_bufsz)
        {
            struct winsize  ws = {.ws_row = 25,.ws_col = 80 };
            fuse_reply_ioctl(req, 0, &ws, sizeof(struct winsize));
        }
        else
        {
            struct iovec    iov = { arg, sizeof(struct winsize) };
            fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
        }
        break;
    default:
        fuse_reply_err(req, ENOSYS);
        return;
    }
}

static void
ttynvt_poll(fuse_req_t req, struct fuse_file_info *info,
            struct fuse_pollhandle *ph)
{
    ttynvt_t       *tty = (ttynvt_t *) (uintptr_t) info->fh;
    int             revents = 0;

    _update_notify(tty, ph);

    if (_write_avail(tty) > 0)
        revents |= POLLOUT;

    if (_read_avail(tty) > 0)
        revents |= POLLIN;

    if (tty->error)
    {
        if (tty->epipe == 0)
            revents = POLLHUP | POLLIN;
        else
            revents = 0;
    }

    fuse_reply_poll(req, revents);
}

static const struct cuse_lowlevel_ops ttynvt_op = {
    .open = ttynvt_open,
    .read = ttynvt_read,
    .write = ttynvt_write,
    .ioctl = ttynvt_ioctl,
    .poll = ttynvt_poll,
    .release = ttynvt_release,
};

#define TTYNET_OPT(t, p, v) { t, offsetof(struct ttynvt_param, p), v }

static const struct fuse_opt ttynvt_opts[] = {
    TTYNET_OPT("-D", debug, 0),
    TTYNET_OPT("-M %u", major, 1),
    TTYNET_OPT("--maj=%u", major, 1),
    TTYNET_OPT("-m %u", minor, 1),
    TTYNET_OPT("--min=%u", minor, 1),
    TTYNET_OPT("-n %s", dev_name, 0),
    TTYNET_OPT("--name=%s", dev_name, 0),
    TTYNET_OPT("-s %s", host, 0),
    TTYNET_OPT("--server=%s", host, 0),
    TTYNET_OPT("-p %u", port, 0),
    TTYNET_OPT("--port=%u", port, 0),
    FUSE_OPT_KEY("-h", 0),
    FUSE_OPT_KEY("--help", 0),
    FUSE_OPT_END
};

static void print_help(void)
{
    fprintf(stderr, "ttynvt Usage:\n"
            "\t-D\tEnable debug\n"
            "\t-M major, --maj=major\n"
            "\t-m minor, --min=minor\n"
            "\t-n name, --name=name (default: ttyNVT0)\n"
            "\t\tDevice will be created in /dev/$name.\n"
            "\t-s server, --server=host name or IP address\n"
            "\t-p port, --port=host port number\n" "\n");
}

static int
process_arg(void *data, const char *arg, int key, struct fuse_args *outargs)
{
    switch (key)
    {
    case 0:
        print_help();
        return fuse_opt_add_arg(outargs, "-ho");
    default:
        return 1;
    }
}

int main(int argc, char *argv[])
{
    struct fuse_args args = FUSE_ARGS_INIT(argc, argv);

    char            dev_name[128];
    const char     *dev_info_argv[] = { dev_name };

    openlog("ttynvt", LOG_PID, LOG_DAEMON);

    if (fuse_opt_parse(&args, &ttynvt_param, ttynvt_opts, process_arg))
    {
        fprintf(stderr, "Failed to parse arguments\n");
        return 1;
    }

    if (!ttynvt_param.dev_name)
        ttynvt_param.dev_name = "ttyNVT0";

    snprintf(dev_name, sizeof(dev_name), "DEVNAME=%s", ttynvt_param.dev_name);

    struct cuse_info ci = {
        .dev_major = ttynvt_param.major,
        .dev_minor = ttynvt_param.minor,
        .dev_info_argc = sizeof(dev_info_argv) / sizeof(char *),
        .dev_info_argv = dev_info_argv,
        .flags = CUSE_UNRESTRICTED_IOCTL,
    };

    return cuse_lowlevel_main(args.argc, args.argv, &ci, &ttynvt_op, NULL);
}