/*
 * slcan.c - serial line CAN interface driver (using tty line discipline)
 *
 * This file is derived from linux/drivers/net/slip/slip.c
 *
 * slip.c Authors  : Laurence Culhane <loz@holmes.demon.co.uk>
 *                   Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
 * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see http://www.gnu.org/licenses/gpl.html
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
 * OWNER 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 <linux/module.h>
#include <linux/moduleparam.h>

#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/string.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/workqueue.h>
#include <linux/can.h>
#include <linux/can/skb.h>

MODULE_ALIAS_LDISC(N_SLCAN);
MODULE_DESCRIPTION("serial line CAN interface");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Oliver Hartkopp <socketcan@hartkopp.net>");

#define SLCAN_MAGIC 0x53CA

static int maxdev = 10;         /* MAX number of SLCAN channels;
                                   This can be overridden with
                                   insmod slcan.ko maxdev=nnn   */
module_param(maxdev, int, 0);
MODULE_PARM_DESC(maxdev, "Maximum number of slcan interfaces");

/* maximum rx buffer len: extended CAN frame with timestamp */
#define SLC_MTU (sizeof("T1111222281122334455667788EA5F\r")+1)

#define SLC_CMD_LEN 1
#define SLC_SFF_ID_LEN 3
#define SLC_EFF_ID_LEN 8

struct slcan {
        int                     magic;

        /* Various fields. */
        struct tty_struct       *tty;           /* ptr to TTY structure      */
        struct net_device       *dev;           /* easy for intr handling    */
        spinlock_t              lock;
        struct work_struct      tx_work;        /* Flushes transmit buffer   */

        /* These are pointers to the malloc()ed frame buffers. */
        unsigned char           rbuff[SLC_MTU]; /* receiver buffer           */
        int                     rcount;         /* received chars counter    */
        unsigned char           xbuff[SLC_MTU]; /* transmitter buffer        */
        unsigned char           *xhead;         /* pointer to next XMIT byte */
        int                     xleft;          /* bytes left in XMIT queue  */

        unsigned long           flags;          /* Flag values/ mode etc     */
#define SLF_INUSE               0               /* Channel in use            */
#define SLF_ERROR               1               /* Parity, etc. error        */
};

static struct net_device **slcan_devs;

 /************************************************************************
  *                     SLCAN ENCAPSULATION FORMAT                       *
  ************************************************************************/

/*
 * A CAN frame has a can_id (11 bit standard frame format OR 29 bit extended
 * frame format) a data length code (can_dlc) which can be from 0 to 8
 * and up to <can_dlc> data bytes as payload.
 * Additionally a CAN frame may become a remote transmission frame if the
 * RTR-bit is set. This causes another ECU to send a CAN frame with the
 * given can_id.
 *
 * The SLCAN ASCII representation of these different frame types is:
 * <type> <id> <dlc> <data>*
 *
 * Extended frames (29 bit) are defined by capital characters in the type.
 * RTR frames are defined as 'r' types - normal frames have 't' type:
 * t => 11 bit data frame
 * r => 11 bit RTR frame
 * T => 29 bit data frame
 * R => 29 bit RTR frame
 *
 * The <id> is 3 (standard) or 8 (extended) bytes in ASCII Hex (base64).
 * The <dlc> is a one byte ASCII number ('0' - '8')
 * The <data> section has at much ASCII Hex bytes as defined by the <dlc>
 *
 * Examples:
 *
 * t1230 : can_id 0x123, can_dlc 0, no data
 * t4563112233 : can_id 0x456, can_dlc 3, data 0x11 0x22 0x33
 * T12ABCDEF2AA55 : extended can_id 0x12ABCDEF, can_dlc 2, data 0xAA 0x55
 * r1230 : can_id 0x123, can_dlc 0, no data, remote transmission request
 *
 */

 /************************************************************************
  *                     STANDARD SLCAN DECAPSULATION                     *
  ************************************************************************/

/* Send one completely decapsulated can_frame to the network layer */
static void slc_bump(struct slcan *sl)
{
        struct sk_buff *skb;
        struct can_frame cf;
        int i, tmp;
        u32 tmpid;
        char *cmd = sl->rbuff;

        cf.can_id = 0;

        switch (*cmd) {
        case 'r':
                cf.can_id = CAN_RTR_FLAG;
                /* fallthrough */
        case 't':
                /* store dlc ASCII value and terminate SFF CAN ID string */
                cf.can_dlc = sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN];
                sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN] = 0;
                /* point to payload data behind the dlc */
                cmd += SLC_CMD_LEN + SLC_SFF_ID_LEN + 1;
                break;
        case 'R':
                cf.can_id = CAN_RTR_FLAG;
                /* fallthrough */
        case 'T':
                cf.can_id |= CAN_EFF_FLAG;
                /* store dlc ASCII value and terminate EFF CAN ID string */
                cf.can_dlc = sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN];
                sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN] = 0;
                /* point to payload data behind the dlc */
                cmd += SLC_CMD_LEN + SLC_EFF_ID_LEN + 1;
                break;
        default:
                return;
        }

        if (kstrtou32(sl->rbuff + SLC_CMD_LEN, 16, &tmpid))
                return;

        cf.can_id |= tmpid;

        /* get can_dlc from sanitized ASCII value */
        if (cf.can_dlc >= '0' && cf.can_dlc < '9')
                cf.can_dlc -= '0';
        else
                return;

        *(u64 *) (&cf.data) = 0; /* clear payload */

        /* RTR frames may have a dlc > 0 but they never have any data bytes */
        if (!(cf.can_id & CAN_RTR_FLAG)) {
                for (i = 0; i < cf.can_dlc; i++) {
                        tmp = hex_to_bin(*cmd++);
                        if (tmp < 0)
                                return;
                        cf.data[i] = (tmp << 4);
                        tmp = hex_to_bin(*cmd++);
                        if (tmp < 0)
                                return;
                        cf.data[i] |= tmp;
                }
        }

        skb = dev_alloc_skb(sizeof(struct can_frame) +
                            sizeof(struct can_skb_priv));
        if (!skb)
                return;

        skb->dev = sl->dev;
        skb->protocol = htons(ETH_P_CAN);
        skb->pkt_type = PACKET_BROADCAST;
        skb->ip_summed = CHECKSUM_UNNECESSARY;

        can_skb_reserve(skb);
        can_skb_prv(skb)->ifindex = sl->dev->ifindex;
        can_skb_prv(skb)->skbcnt = 0;

        memcpy(skb_put(skb, sizeof(struct can_frame)),
               &cf, sizeof(struct can_frame));

        sl->dev->stats.rx_packets++;
        sl->dev->stats.rx_bytes += cf.can_dlc;
        netif_rx_ni(skb);
}

/* parse tty input stream */
static void slcan_unesc(struct slcan *sl, unsigned char s)
{
        if ((s == '\r') || (s == '\a')) { /* CR or BEL ends the pdu */
                if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
                    (sl->rcount > 4))  {
                        slc_bump(sl);
                }
                sl->rcount = 0;
        } else {
                if (!test_bit(SLF_ERROR, &sl->flags))  {
                        if (sl->rcount < SLC_MTU)  {
                                sl->rbuff[sl->rcount++] = s;
                                return;
                        } else {
                                sl->dev->stats.rx_over_errors++;
                                set_bit(SLF_ERROR, &sl->flags);
                        }
                }
        }
}

 /************************************************************************
  *                     STANDARD SLCAN ENCAPSULATION                     *
  ************************************************************************/

/* Encapsulate one can_frame and stuff into a TTY queue. */
static void slc_encaps(struct slcan *sl, struct can_frame *cf)
{
        int actual, i;
        unsigned char *pos;
        unsigned char *endpos;
        canid_t id = cf->can_id;

        pos = sl->xbuff;

        if (cf->can_id & CAN_RTR_FLAG)
                *pos = 'R'; /* becomes 'r' in standard frame format (SFF) */
        else
                *pos = 'T'; /* becomes 't' in standard frame format (SSF) */

        /* determine number of chars for the CAN-identifier */
        if (cf->can_id & CAN_EFF_FLAG) {
                id &= CAN_EFF_MASK;
                endpos = pos + SLC_EFF_ID_LEN;
        } else {
                *pos |= 0x20; /* convert R/T to lower case for SFF */
                id &= CAN_SFF_MASK;
                endpos = pos + SLC_SFF_ID_LEN;
        }

        /* build 3 (SFF) or 8 (EFF) digit CAN identifier */
        pos++;
        while (endpos >= pos) {
                *endpos-- = hex_asc_upper[id & 0xf];
                id >>= 4;
        }

        pos += (cf->can_id & CAN_EFF_FLAG) ? SLC_EFF_ID_LEN : SLC_SFF_ID_LEN;

        *pos++ = cf->can_dlc + '0';

        /* RTR frames may have a dlc > 0 but they never have any data bytes */
        if (!(cf->can_id & CAN_RTR_FLAG)) {
                for (i = 0; i < cf->can_dlc; i++)
                        pos = hex_byte_pack_upper(pos, cf->data[i]);
        }

        *pos++ = '\r';

        /* Order of next two lines is *very* important.
         * When we are sending a little amount of data,
         * the transfer may be completed inside the ops->write()
         * routine, because it's running with interrupts enabled.
         * In this case we *never* got WRITE_WAKEUP event,
         * if we did not request it before write operation.
         *       14 Oct 1994  Dmitry Gorodchanin.
         */
        set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
        actual = sl->tty->ops->write(sl->tty, sl->xbuff, pos - sl->xbuff);
        sl->xleft = (pos - sl->xbuff) - actual;
        sl->xhead = sl->xbuff + actual;
        sl->dev->stats.tx_bytes += cf->can_dlc;
}

/* Write out any remaining transmit buffer. Scheduled when tty is writable */
static void slcan_transmit(struct work_struct *work)
{
        struct slcan *sl = container_of(work, struct slcan, tx_work);
        int actual;

        spin_lock_bh(&sl->lock);
        /* First make sure we're connected. */
        if (!sl->tty || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev)) {
                spin_unlock_bh(&sl->lock);
                return;
        }

        if (sl->xleft <= 0)  {
                /* Now serial buffer is almost free & we can start
                 * transmission of another packet */
                sl->dev->stats.tx_packets++;
                clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
                spin_unlock_bh(&sl->lock);
                netif_wake_queue(sl->dev);
                return;
        }

        actual = sl->tty->ops->write(sl->tty, sl->xhead, sl->xleft);
        sl->xleft -= actual;
        sl->xhead += actual;
        spin_unlock_bh(&sl->lock);
}

/*
 * Called by the driver when there's room for more data.
 * Schedule the transmit.
 */
static void slcan_write_wakeup(struct tty_struct *tty)
{
        struct slcan *sl = tty->disc_data;

        schedule_work(&sl->tx_work);
}

/* Send a can_frame to a TTY queue. */
static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct slcan *sl = netdev_priv(dev);

        if (skb->len != sizeof(struct can_frame))
                goto out;

        spin_lock(&sl->lock);
        if (!netif_running(dev))  {
                spin_unlock(&sl->lock);
                printk(KERN_WARNING "%s: xmit: iface is down\n", dev->name);
                goto out;
        }
        if (sl->tty == NULL) {
                spin_unlock(&sl->lock);
                goto out;
        }

        netif_stop_queue(sl->dev);
        slc_encaps(sl, (struct can_frame *) skb->data); /* encaps & send */
        spin_unlock(&sl->lock);

out:
        kfree_skb(skb);
        return NETDEV_TX_OK;
}


/******************************************
 *   Routines looking at netdevice side.
 ******************************************/

/* Netdevice UP -> DOWN routine */
static int slc_close(struct net_device *dev)
{
        struct slcan *sl = netdev_priv(dev);

        spin_lock_bh(&sl->lock);
        if (sl->tty) {
                /* TTY discipline is running. */
                clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
        }
        netif_stop_queue(dev);
        sl->rcount   = 0;
        sl->xleft    = 0;
        spin_unlock_bh(&sl->lock);

        return 0;
}

/* Netdevice DOWN -> UP routine */
static int slc_open(struct net_device *dev)
{
        struct slcan *sl = netdev_priv(dev);

        if (sl->tty == NULL)
                return -ENODEV;

        sl->flags &= (1 << SLF_INUSE);
        netif_start_queue(dev);
        return 0;
}

/* Hook the destructor so we can free slcan devs at the right point in time */
static void slc_free_netdev(struct net_device *dev)
{
        int i = dev->base_addr;
        free_netdev(dev);
        slcan_devs[i] = NULL;
}

static int slcan_change_mtu(struct net_device *dev, int new_mtu)
{
        return -EINVAL;
}

static const struct net_device_ops slc_netdev_ops = {
        .ndo_open               = slc_open,
        .ndo_stop               = slc_close,
        .ndo_start_xmit         = slc_xmit,
        .ndo_change_mtu         = slcan_change_mtu,
};

static void slc_setup(struct net_device *dev)
{
        dev->netdev_ops         = &slc_netdev_ops;
        dev->destructor         = slc_free_netdev;

        dev->hard_header_len    = 0;
        dev->addr_len           = 0;
        dev->tx_queue_len       = 10;

        dev->mtu                = sizeof(struct can_frame);
        dev->type               = ARPHRD_CAN;

        /* New-style flags. */
        dev->flags              = IFF_NOARP;
        dev->features           = NETIF_F_HW_CSUM;
}

/******************************************
  Routines looking at TTY side.
 ******************************************/

/*
 * Handle the 'receiver data ready' interrupt.
 * This function is called by the 'tty_io' module in the kernel when
 * a block of SLCAN data has been received, which can now be decapsulated
 * and sent on to some IP layer for further processing. This will not
 * be re-entered while running but other ldisc functions may be called
 * in parallel
 */

static void slcan_receive_buf(struct tty_struct *tty,
                              const unsigned char *cp, char *fp, int count)
{
        struct slcan *sl = (struct slcan *) tty->disc_data;

        if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
                return;

        /* Read the characters out of the buffer */
        while (count--) {
                if (fp && *fp++) {
                        if (!test_and_set_bit(SLF_ERROR, &sl->flags))
                                sl->dev->stats.rx_errors++;
                        cp++;
                        continue;
                }
                slcan_unesc(sl, *cp++);
        }
}

/************************************
 *  slcan_open helper routines.
 ************************************/

/* Collect hanged up channels */
static void slc_sync(void)
{
        int i;
        struct net_device *dev;
        struct slcan      *sl;

        for (i = 0; i < maxdev; i++) {
                dev = slcan_devs[i];
                if (dev == NULL)
                        break;

                sl = netdev_priv(dev);
                if (sl->tty)
                        continue;
                if (dev->flags & IFF_UP)
                        dev_close(dev);
        }
}

/* Find a free SLCAN channel, and link in this `tty' line. */
static struct slcan *slc_alloc(dev_t line)
{
        int i;
        char name[IFNAMSIZ];
        struct net_device *dev = NULL;
        struct slcan       *sl;

        for (i = 0; i < maxdev; i++) {
                dev = slcan_devs[i];
                if (dev == NULL)
                        break;

        }

        /* Sorry, too many, all slots in use */
        if (i >= maxdev)
                return NULL;

        sprintf(name, "slcan%d", i);
        dev = alloc_netdev(sizeof(*sl), name, NET_NAME_UNKNOWN, slc_setup);
        if (!dev)
                return NULL;

        dev->base_addr  = i;
        sl = netdev_priv(dev);

        /* Initialize channel control data */
        sl->magic = SLCAN_MAGIC;
        sl->dev = dev;
        spin_lock_init(&sl->lock);
        INIT_WORK(&sl->tx_work, slcan_transmit);
        slcan_devs[i] = dev;

        return sl;
}

/*
 * Open the high-level part of the SLCAN channel.
 * This function is called by the TTY module when the
 * SLCAN line discipline is called for.  Because we are
 * sure the tty line exists, we only have to link it to
 * a free SLCAN channel...
 *
 * Called in process context serialized from other ldisc calls.
 */

static int slcan_open(struct tty_struct *tty)
{
        struct slcan *sl;
        int err;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        if (tty->ops->write == NULL)
                return -EOPNOTSUPP;

        /* RTnetlink lock is misused here to serialize concurrent
           opens of slcan channels. There are better ways, but it is
           the simplest one.
         */
        rtnl_lock();

        /* Collect hanged up channels. */
        slc_sync();

        sl = tty->disc_data;

        err = -EEXIST;
        /* First make sure we're not already connected. */
        if (sl && sl->magic == SLCAN_MAGIC)
                goto err_exit;

        /* OK.  Find a free SLCAN channel to use. */
        err = -ENFILE;
        sl = slc_alloc(tty_devnum(tty));
        if (sl == NULL)
                goto err_exit;

        sl->tty = tty;
        tty->disc_data = sl;

        if (!test_bit(SLF_INUSE, &sl->flags)) {
                /* Perform the low-level SLCAN initialization. */
                sl->rcount   = 0;
                sl->xleft    = 0;

                set_bit(SLF_INUSE, &sl->flags);

                err = register_netdevice(sl->dev);
                if (err)
                        goto err_free_chan;
        }

        /* Done.  We have linked the TTY line to a channel. */
        rtnl_unlock();
        tty->receive_room = 65536;      /* We don't flow control */

        /* TTY layer expects 0 on success */
        return 0;

err_free_chan:
        sl->tty = NULL;
        tty->disc_data = NULL;
        clear_bit(SLF_INUSE, &sl->flags);

err_exit:
        rtnl_unlock();

        /* Count references from TTY module */
        return err;
}

/*
 * Close down a SLCAN channel.
 * This means flushing out any pending queues, and then returning. This
 * call is serialized against other ldisc functions.
 *
 * We also use this method for a hangup event.
 */

static void slcan_close(struct tty_struct *tty)
{
        struct slcan *sl = (struct slcan *) tty->disc_data;

        /* First make sure we're connected. */
        if (!sl || sl->magic != SLCAN_MAGIC || sl->tty != tty)
                return;

        spin_lock_bh(&sl->lock);
        tty->disc_data = NULL;
        sl->tty = NULL;
        spin_unlock_bh(&sl->lock);

        flush_work(&sl->tx_work);

        /* Flush network side */
        unregister_netdev(sl->dev);
        /* This will complete via sl_free_netdev */
}

static int slcan_hangup(struct tty_struct *tty)
{
        slcan_close(tty);
        return 0;
}

/* Perform I/O control on an active SLCAN channel. */
static int slcan_ioctl(struct tty_struct *tty, struct file *file,
                       unsigned int cmd, unsigned long arg)
{
        struct slcan *sl = (struct slcan *) tty->disc_data;
        unsigned int tmp;

        /* First make sure we're connected. */
        if (!sl || sl->magic != SLCAN_MAGIC)
                return -EINVAL;

        switch (cmd) {
        case SIOCGIFNAME:
                tmp = strlen(sl->dev->name) + 1;
                if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
                        return -EFAULT;
                return 0;

        case SIOCSIFHWADDR:
                return -EINVAL;

        default:
                return tty_mode_ioctl(tty, file, cmd, arg);
        }
}

static struct tty_ldisc_ops slc_ldisc = {
        .owner          = THIS_MODULE,
        .magic          = TTY_LDISC_MAGIC,
        .name           = "slcan",
        .open           = slcan_open,
        .close          = slcan_close,
        .hangup         = slcan_hangup,
        .ioctl          = slcan_ioctl,
        .receive_buf    = slcan_receive_buf,
        .write_wakeup   = slcan_write_wakeup,
};

static int __init slcan_init(void)
{
        int status;

        if (maxdev < 4)
                maxdev = 4; /* Sanity */

        pr_info("slcan: serial line CAN interface driver\n");
        pr_info("slcan: %d dynamic interface channels.\n", maxdev);

        slcan_devs = kzalloc(sizeof(struct net_device *)*maxdev, GFP_KERNEL);
        if (!slcan_devs)
                return -ENOMEM;

        /* Fill in our line protocol discipline, and register it */
        status = tty_register_ldisc(N_SLCAN, &slc_ldisc);
        if (status)  {
                printk(KERN_ERR "slcan: can't register line discipline\n");
                kfree(slcan_devs);
        }
        return status;
}

static void __exit slcan_exit(void)
{
        int i;
        struct net_device *dev;
        struct slcan *sl;
        unsigned long timeout = jiffies + HZ;
        int busy = 0;

        if (slcan_devs == NULL)
                return;

        /* First of all: check for active disciplines and hangup them.
         */
        do {
                if (busy)
                        msleep_interruptible(100);

                busy = 0;
                for (i = 0; i < maxdev; i++) {
                        dev = slcan_devs[i];
                        if (!dev)
                                continue;
                        sl = netdev_priv(dev);
                        spin_lock_bh(&sl->lock);
                        if (sl->tty) {
                                busy++;
                                tty_hangup(sl->tty);
                        }
                        spin_unlock_bh(&sl->lock);
                }
        } while (busy && time_before(jiffies, timeout));

        /* FIXME: hangup is async so we should wait when doing this second
           phase */

        for (i = 0; i < maxdev; i++) {
                dev = slcan_devs[i];
                if (!dev)
                        continue;
                slcan_devs[i] = NULL;

                sl = netdev_priv(dev);
                if (sl->tty) {
                        printk(KERN_ERR "%s: tty discipline still running\n",
                               dev->name);
                        /* Intentionally leak the control block. */
                        dev->destructor = NULL;
                }

                unregister_netdev(dev);
        }

        kfree(slcan_devs);
        slcan_devs = NULL;

        i = tty_unregister_ldisc(N_SLCAN);
        if (i)
                printk(KERN_ERR "slcan: can't unregister ldisc (err %d)\n", i);
}

module_init(slcan_init);
module_exit(slcan_exit);