// SPDX-License-Identifier: GPL-2.0-only
/*
 * slip.c       This module implements the SLIP protocol for kernel-based
 *              devices like TTY.  It interfaces between a raw TTY, and the
 *              kernel's INET protocol layers.
 *
 * Version:     @(#)slip.c      0.8.3   12/24/94
 *
 * Authors:     Laurence Culhane, <loz@holmes.demon.co.uk>
 *              Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
 *
 * Fixes:
 *              Alan Cox        :       Sanity checks and avoid tx overruns.
 *                                      Has a new sl->mtu field.
 *              Alan Cox        :       Found cause of overrun. ifconfig sl0
 *                                      mtu upwards. Driver now spots this
 *                                      and grows/shrinks its buffers(hack!).
 *                                      Memory leak if you run out of memory
 *                                      setting up a slip driver fixed.
 *              Matt Dillon     :       Printable slip (borrowed from NET2E)
 *      Pauline Middelink       :       Slip driver fixes.
 *              Alan Cox        :       Honours the old SL_COMPRESSED flag
 *              Alan Cox        :       KISS AX.25 and AXUI IP support
 *              Michael Riepe   :       Automatic CSLIP recognition added
 *              Charles Hedrick :       CSLIP header length problem fix.
 *              Alan Cox        :       Corrected non-IP cases of the above.
 *              Alan Cox        :       Now uses hardware type as per FvK.
 *              Alan Cox        :       Default to 192.168.0.0 (RFC 1597)
 *              A.N.Kuznetsov   :       dev_tint() recursion fix.
 *      Dmitry Gorodchanin      :       SLIP memory leaks
 *      Dmitry Gorodchanin      :       Code cleanup. Reduce tty driver
 *                                      buffering from 4096 to 256 bytes.
 *                                      Improving SLIP response time.
 *                                      CONFIG_SLIP_MODE_SLIP6.
 *                                      ifconfig sl? up & down now works
 *                                      correctly.
 *                                      Modularization.
 *              Alan Cox        :       Oops - fix AX.25 buffer lengths
 *      Dmitry Gorodchanin      :       Even more cleanups. Preserve CSLIP
 *                                      statistics. Include CSLIP code only
 *                                      if it really needed.
 *              Alan Cox        :       Free slhc buffers in the right place.
 *              Alan Cox        :       Allow for digipeated IP over AX.25
 *              Matti Aarnio    :       Dynamic SLIP devices, with ideas taken
 *                                      from Jim Freeman's <jfree@caldera.com>
 *                                      dynamic PPP devices.  We do NOT kfree()
 *                                      device entries, just reg./unreg. them
 *                                      as they are needed.  We kfree() them
 *                                      at module cleanup.
 *                                      With MODULE-loading ``insmod'', user
 *                                      can issue parameter:  slip_maxdev=1024
 *                                      (Or how much he/she wants.. Default
 *                                      is 256)
 *      Stanislav Voronyi       :       Slip line checking, with ideas taken
 *                                      from multislip BSDI driver which was
 *                                      written by Igor Chechik, RELCOM Corp.
 *                                      Only algorithms have been ported to
 *                                      Linux SLIP driver.
 *      Vitaly E. Lavrov        :       Sane behaviour on tty hangup.
 *      Alexey Kuznetsov        :       Cleanup interfaces to tty & netdevice
 *                                      modules.
 */

#define SL_CHECK_TRANSMIT
#include <linux/compat.h>
#include <linux/module.h>
#include <linux/moduleparam.h>

#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/sched/signal.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/if_arp.h>
#include <linux/if_slip.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include "slip.h"
#ifdef CONFIG_INET
#include <linux/ip.h>
#include <linux/tcp.h>
#include <net/slhc_vj.h>
#endif

#define SLIP_VERSION    "0.8.4-NET3.019-NEWTTY"

static struct net_device **slip_devs;

static int slip_maxdev = SL_NRUNIT;
module_param(slip_maxdev, int, 0);
MODULE_PARM_DESC(slip_maxdev, "Maximum number of slip devices");

static int slip_esc(unsigned char *p, unsigned char *d, int len);
static void slip_unesc(struct slip *sl, unsigned char c);
#ifdef CONFIG_SLIP_MODE_SLIP6
static int slip_esc6(unsigned char *p, unsigned char *d, int len);
static void slip_unesc6(struct slip *sl, unsigned char c);
#endif
#ifdef CONFIG_SLIP_SMART
static void sl_keepalive(struct timer_list *t);
static void sl_outfill(struct timer_list *t);
static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq, void __user *data, int cmd);
#endif

/********************************
*  Buffer administration routines:
*       sl_alloc_bufs()
*       sl_free_bufs()
*       sl_realloc_bufs()
*
* NOTE: sl_realloc_bufs != sl_free_bufs + sl_alloc_bufs, because
*       sl_realloc_bufs provides strong atomicity and reallocation
*       on actively running device.
*********************************/

/*
   Allocate channel buffers.
 */

static int sl_alloc_bufs(struct slip *sl, int mtu)
{
        int err = -ENOBUFS;
        unsigned long len;
        char *rbuff = NULL;
        char *xbuff = NULL;
#ifdef SL_INCLUDE_CSLIP
        char *cbuff = NULL;
        struct slcompress *slcomp = NULL;
#endif

        /*
         * Allocate the SLIP frame buffers:
         *
         * rbuff        Receive buffer.
         * xbuff        Transmit buffer.
         * cbuff        Temporary compression buffer.
         */
        len = mtu * 2;

        /*
         * allow for arrival of larger UDP packets, even if we say not to
         * also fixes a bug in which SunOS sends 512-byte packets even with
         * an MSS of 128
         */
        if (len < 576 * 2)
                len = 576 * 2;
        rbuff = kmalloc(len + 4, GFP_KERNEL);
        if (rbuff == NULL)
                goto err_exit;
        xbuff = kmalloc(len + 4, GFP_KERNEL);
        if (xbuff == NULL)
                goto err_exit;
#ifdef SL_INCLUDE_CSLIP
        cbuff = kmalloc(len + 4, GFP_KERNEL);
        if (cbuff == NULL)
                goto err_exit;
        slcomp = slhc_init(16, 16);
        if (IS_ERR(slcomp))
                goto err_exit;
#endif
        spin_lock_bh(&sl->lock);
        if (sl->tty == NULL) {
                spin_unlock_bh(&sl->lock);
                err = -ENODEV;
                goto err_exit;
        }
        sl->mtu      = mtu;
        sl->buffsize = len;
        sl->rcount   = 0;
        sl->xleft    = 0;
        rbuff = xchg(&sl->rbuff, rbuff);
        xbuff = xchg(&sl->xbuff, xbuff);
#ifdef SL_INCLUDE_CSLIP
        cbuff = xchg(&sl->cbuff, cbuff);
        slcomp = xchg(&sl->slcomp, slcomp);
#endif
#ifdef CONFIG_SLIP_MODE_SLIP6
        sl->xdata    = 0;
        sl->xbits    = 0;
#endif
        spin_unlock_bh(&sl->lock);
        err = 0;

        /* Cleanup */
err_exit:
#ifdef SL_INCLUDE_CSLIP
        kfree(cbuff);
        slhc_free(slcomp);
#endif
        kfree(xbuff);
        kfree(rbuff);
        return err;
}

/* Free a SLIP channel buffers. */
static void sl_free_bufs(struct slip *sl)
{
        /* Free all SLIP frame buffers. */
        kfree(xchg(&sl->rbuff, NULL));
        kfree(xchg(&sl->xbuff, NULL));
#ifdef SL_INCLUDE_CSLIP
        kfree(xchg(&sl->cbuff, NULL));
        slhc_free(xchg(&sl->slcomp, NULL));
#endif
}

/*
   Reallocate slip channel buffers.
 */

static int sl_realloc_bufs(struct slip *sl, int mtu)
{
        int err = 0;
        struct net_device *dev = sl->dev;
        unsigned char *xbuff, *rbuff;
#ifdef SL_INCLUDE_CSLIP
        unsigned char *cbuff;
#endif
        int len = mtu * 2;

/*
 * allow for arrival of larger UDP packets, even if we say not to
 * also fixes a bug in which SunOS sends 512-byte packets even with
 * an MSS of 128
 */
        if (len < 576 * 2)
                len = 576 * 2;

        xbuff = kmalloc(len + 4, GFP_ATOMIC);
        rbuff = kmalloc(len + 4, GFP_ATOMIC);
#ifdef SL_INCLUDE_CSLIP
        cbuff = kmalloc(len + 4, GFP_ATOMIC);
#endif


#ifdef SL_INCLUDE_CSLIP
        if (xbuff == NULL || rbuff == NULL || cbuff == NULL)  {
#else
        if (xbuff == NULL || rbuff == NULL)  {
#endif
                if (mtu > sl->mtu) {
                        printk(KERN_WARNING "%s: unable to grow slip buffers, MTU change cancelled.\n",
                               dev->name);
                        err = -ENOBUFS;
                }
                goto done;
        }
        spin_lock_bh(&sl->lock);

        err = -ENODEV;
        if (sl->tty == NULL)
                goto done_on_bh;

        xbuff    = xchg(&sl->xbuff, xbuff);
        rbuff    = xchg(&sl->rbuff, rbuff);
#ifdef SL_INCLUDE_CSLIP
        cbuff    = xchg(&sl->cbuff, cbuff);
#endif
        if (sl->xleft)  {
                if (sl->xleft <= len)  {
                        memcpy(sl->xbuff, sl->xhead, sl->xleft);
                } else  {
                        sl->xleft = 0;
                        dev->stats.tx_dropped++;
                }
        }
        sl->xhead = sl->xbuff;

        if (sl->rcount)  {
                if (sl->rcount <= len) {
                        memcpy(sl->rbuff, rbuff, sl->rcount);
                } else  {
                        sl->rcount = 0;
                        dev->stats.rx_over_errors++;
                        set_bit(SLF_ERROR, &sl->flags);
                }
        }
        sl->mtu      = mtu;
        dev->mtu      = mtu;
        sl->buffsize = len;
        err = 0;

done_on_bh:
        spin_unlock_bh(&sl->lock);

done:
        kfree(xbuff);
        kfree(rbuff);
#ifdef SL_INCLUDE_CSLIP
        kfree(cbuff);
#endif
        return err;
}


/* Set the "sending" flag.  This must be atomic hence the set_bit. */
static inline void sl_lock(struct slip *sl)
{
        netif_stop_queue(sl->dev);
}


/* Clear the "sending" flag.  This must be atomic, hence the ASM. */
static inline void sl_unlock(struct slip *sl)
{
        netif_wake_queue(sl->dev);
}

/* Send one completely decapsulated IP datagram to the IP layer. */
static void sl_bump(struct slip *sl)
{
        struct net_device *dev = sl->dev;
        struct sk_buff *skb;
        int count;

        count = sl->rcount;
#ifdef SL_INCLUDE_CSLIP
        if (sl->mode & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) {
                unsigned char c = sl->rbuff[0];
                if (c & SL_TYPE_COMPRESSED_TCP) {
                        /* ignore compressed packets when CSLIP is off */
                        if (!(sl->mode & SL_MODE_CSLIP)) {
                                printk(KERN_WARNING "%s: compressed packet ignored\n", dev->name);
                                return;
                        }
                        /* make sure we've reserved enough space for uncompress
                           to use */
                        if (count + 80 > sl->buffsize) {
                                dev->stats.rx_over_errors++;
                                return;
                        }
                        count = slhc_uncompress(sl->slcomp, sl->rbuff, count);
                        if (count <= 0)
                                return;
                } else if (c >= SL_TYPE_UNCOMPRESSED_TCP) {
                        if (!(sl->mode & SL_MODE_CSLIP)) {
                                /* turn on header compression */
                                sl->mode |= SL_MODE_CSLIP;
                                sl->mode &= ~SL_MODE_ADAPTIVE;
                                printk(KERN_INFO "%s: header compression turned on\n", dev->name);
                        }
                        sl->rbuff[0] &= 0x4f;
                        if (slhc_remember(sl->slcomp, sl->rbuff, count) <= 0)
                                return;
                }
        }
#endif  /* SL_INCLUDE_CSLIP */

        dev->stats.rx_bytes += count;

        skb = dev_alloc_skb(count);
        if (skb == NULL) {
                printk(KERN_WARNING "%s: memory squeeze, dropping packet.\n", dev->name);
                dev->stats.rx_dropped++;
                return;
        }
        skb->dev = dev;
        skb_put_data(skb, sl->rbuff, count);
        skb_reset_mac_header(skb);
        skb->protocol = htons(ETH_P_IP);
        netif_rx_ni(skb);
        dev->stats.rx_packets++;
}

/* Encapsulate one IP datagram and stuff into a TTY queue. */
static void sl_encaps(struct slip *sl, unsigned char *icp, int len)
{
        unsigned char *p;
        int actual, count;

        if (len > sl->mtu) {            /* Sigh, shouldn't occur BUT ... */
                printk(KERN_WARNING "%s: truncating oversized transmit packet!\n", sl->dev->name);
                sl->dev->stats.tx_dropped++;
                sl_unlock(sl);
                return;
        }

        p = icp;
#ifdef SL_INCLUDE_CSLIP
        if (sl->mode & SL_MODE_CSLIP)
                len = slhc_compress(sl->slcomp, p, len, sl->cbuff, &p, 1);
#endif
#ifdef CONFIG_SLIP_MODE_SLIP6
        if (sl->mode & SL_MODE_SLIP6)
                count = slip_esc6(p, sl->xbuff, len);
        else
#endif
                count = slip_esc(p, sl->xbuff, len);

        /* 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, count);
#ifdef SL_CHECK_TRANSMIT
        netif_trans_update(sl->dev);
#endif
        sl->xleft = count - actual;
        sl->xhead = sl->xbuff + actual;
#ifdef CONFIG_SLIP_SMART
        /* VSV */
        clear_bit(SLF_OUTWAIT, &sl->flags);     /* reset outfill flag */
#endif
}

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

        spin_lock_bh(&sl->lock);
        /* First make sure we're connected. */
        if (!sl->tty || sl->magic != SLIP_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);
                sl_unlock(sl);
                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 slip_write_wakeup(struct tty_struct *tty)
{
        struct slip *sl;

        rcu_read_lock();
        sl = rcu_dereference(tty->disc_data);
        if (sl)
                schedule_work(&sl->tx_work);
        rcu_read_unlock();
}

static void sl_tx_timeout(struct net_device *dev, unsigned int txqueue)
{
        struct slip *sl = netdev_priv(dev);

        spin_lock(&sl->lock);

        if (netif_queue_stopped(dev)) {
                if (!netif_running(dev))
                        goto out;

                /* May be we must check transmitter timeout here ?
                 *      14 Oct 1994 Dmitry Gorodchanin.
                 */
#ifdef SL_CHECK_TRANSMIT
                if (time_before(jiffies, dev_trans_start(dev) + 20 * HZ))  {
                        /* 20 sec timeout not reached */
                        goto out;
                }
                printk(KERN_WARNING "%s: transmit timed out, %s?\n",
                        dev->name,
                        (tty_chars_in_buffer(sl->tty) || sl->xleft) ?
                                "bad line quality" : "driver error");
                sl->xleft = 0;
                clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
                sl_unlock(sl);
#endif
        }
out:
        spin_unlock(&sl->lock);
}


/* Encapsulate an IP datagram and kick it into a TTY queue. */
static netdev_tx_t
sl_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct slip *sl = netdev_priv(dev);

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

        sl_lock(sl);
        dev->stats.tx_bytes += skb->len;
        sl_encaps(sl, skb->data, skb->len);
        spin_unlock(&sl->lock);

        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}


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

/* Netdevice UP -> DOWN routine */

static int
sl_close(struct net_device *dev)
{
        struct slip *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 sl_open(struct net_device *dev)
{
        struct slip *sl = netdev_priv(dev);

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

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

/* Netdevice change MTU request */

static int sl_change_mtu(struct net_device *dev, int new_mtu)
{
        struct slip *sl = netdev_priv(dev);

        return sl_realloc_bufs(sl, new_mtu);
}

/* Netdevice get statistics request */

static void
sl_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
{
        struct net_device_stats *devstats = &dev->stats;
#ifdef SL_INCLUDE_CSLIP
        struct slip *sl = netdev_priv(dev);
        struct slcompress *comp = sl->slcomp;
#endif
        stats->rx_packets     = devstats->rx_packets;
        stats->tx_packets     = devstats->tx_packets;
        stats->rx_bytes       = devstats->rx_bytes;
        stats->tx_bytes       = devstats->tx_bytes;
        stats->rx_dropped     = devstats->rx_dropped;
        stats->tx_dropped     = devstats->tx_dropped;
        stats->tx_errors      = devstats->tx_errors;
        stats->rx_errors      = devstats->rx_errors;
        stats->rx_over_errors = devstats->rx_over_errors;

#ifdef SL_INCLUDE_CSLIP
        if (comp) {
                /* Generic compressed statistics */
                stats->rx_compressed   = comp->sls_i_compressed;
                stats->tx_compressed   = comp->sls_o_compressed;

                /* Are we really still needs this? */
                stats->rx_fifo_errors += comp->sls_i_compressed;
                stats->rx_dropped     += comp->sls_i_tossed;
                stats->tx_fifo_errors += comp->sls_o_compressed;
                stats->collisions     += comp->sls_o_misses;
        }
#endif
}

/* Netdevice register callback */

static int sl_init(struct net_device *dev)
{
        struct slip *sl = netdev_priv(dev);

        /*
         *      Finish setting up the DEVICE info.
         */

        dev->mtu                = sl->mtu;
        dev->type               = ARPHRD_SLIP + sl->mode;
#ifdef SL_CHECK_TRANSMIT
        dev->watchdog_timeo     = 20*HZ;
#endif
        return 0;
}


static void sl_uninit(struct net_device *dev)
{
        struct slip *sl = netdev_priv(dev);

        sl_free_bufs(sl);
}

/* Hook the destructor so we can free slip devices at the right point in time */
static void sl_free_netdev(struct net_device *dev)
{
        int i = dev->base_addr;

        slip_devs[i] = NULL;
}

static const struct net_device_ops sl_netdev_ops = {
        .ndo_init               = sl_init,
        .ndo_uninit             = sl_uninit,
        .ndo_open               = sl_open,
        .ndo_stop               = sl_close,
        .ndo_start_xmit         = sl_xmit,
        .ndo_get_stats64        = sl_get_stats64,
        .ndo_change_mtu         = sl_change_mtu,
        .ndo_tx_timeout         = sl_tx_timeout,
#ifdef CONFIG_SLIP_SMART
        .ndo_siocdevprivate     = sl_siocdevprivate,
#endif
};


static void sl_setup(struct net_device *dev)
{
        dev->netdev_ops         = &sl_netdev_ops;
        dev->needs_free_netdev  = true;
        dev->priv_destructor    = sl_free_netdev;

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

        /* MTU range: 68 - 65534 */
        dev->min_mtu = 68;
        dev->max_mtu = 65534;

        /* New-style flags. */
        dev->flags              = IFF_NOARP|IFF_POINTOPOINT|IFF_MULTICAST;
}

/******************************************
  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 SLIP 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 slip_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                const char *fp, int count)
{
        struct slip *sl = tty->disc_data;

        if (!sl || sl->magic != SLIP_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;
                }
#ifdef CONFIG_SLIP_MODE_SLIP6
                if (sl->mode & SL_MODE_SLIP6)
                        slip_unesc6(sl, *cp++);
                else
#endif
                        slip_unesc(sl, *cp++);
        }
}

/************************************
 *  slip_open helper routines.
 ************************************/

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

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

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


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

        for (i = 0; i < slip_maxdev; i++) {
                dev = slip_devs[i];
                if (dev == NULL)
                        break;
        }
        /* Sorry, too many, all slots in use */
        if (i >= slip_maxdev)
                return NULL;

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

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

        /* Initialize channel control data */
        sl->magic       = SLIP_MAGIC;
        sl->dev         = dev;
        spin_lock_init(&sl->lock);
        INIT_WORK(&sl->tx_work, slip_transmit);
        sl->mode        = SL_MODE_DEFAULT;
#ifdef CONFIG_SLIP_SMART
        /* initialize timer_list struct */
        timer_setup(&sl->keepalive_timer, sl_keepalive, 0);
        timer_setup(&sl->outfill_timer, sl_outfill, 0);
#endif
        slip_devs[i] = dev;
        return sl;
}

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

static int slip_open(struct tty_struct *tty)
{
        struct slip *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 slip channels. There are better ways, but it is
           the simplest one.
         */
        rtnl_lock();

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

        sl = tty->disc_data;

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

        /* OK.  Find a free SLIP channel to use. */
        err = -ENFILE;
        sl = sl_alloc();
        if (sl == NULL)
                goto err_exit;

        sl->tty = tty;
        tty->disc_data = sl;
        sl->pid = current->pid;

        if (!test_bit(SLF_INUSE, &sl->flags)) {
                /* Perform the low-level SLIP initialization. */
                err = sl_alloc_bufs(sl, SL_MTU);
                if (err)
                        goto err_free_chan;

                set_bit(SLF_INUSE, &sl->flags);

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

#ifdef CONFIG_SLIP_SMART
        if (sl->keepalive) {
                sl->keepalive_timer.expires = jiffies + sl->keepalive * HZ;
                add_timer(&sl->keepalive_timer);
        }
        if (sl->outfill) {
                sl->outfill_timer.expires = jiffies + sl->outfill * HZ;
                add_timer(&sl->outfill_timer);
        }
#endif

        /* 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_bufs:
        sl_free_bufs(sl);

err_free_chan:
        sl->tty = NULL;
        tty->disc_data = NULL;
        clear_bit(SLF_INUSE, &sl->flags);
        sl_free_netdev(sl->dev);
        /* do not call free_netdev before rtnl_unlock */
        rtnl_unlock();
        free_netdev(sl->dev);
        return err;

err_exit:
        rtnl_unlock();

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

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

static void slip_close(struct tty_struct *tty)
{
        struct slip *sl = tty->disc_data;

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

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

        synchronize_rcu();
        flush_work(&sl->tx_work);

        /* VSV = very important to remove timers */
#ifdef CONFIG_SLIP_SMART
        del_timer_sync(&sl->keepalive_timer);
        del_timer_sync(&sl->outfill_timer);
#endif
        /* Flush network side */
        unregister_netdev(sl->dev);
        /* This will complete via sl_free_netdev */
}

static void slip_hangup(struct tty_struct *tty)
{
        slip_close(tty);
}
 /************************************************************************
  *                     STANDARD SLIP ENCAPSULATION                      *
  ************************************************************************/

static int slip_esc(unsigned char *s, unsigned char *d, int len)
{
        unsigned char *ptr = d;
        unsigned char c;

        /*
         * Send an initial END character to flush out any
         * data that may have accumulated in the receiver
         * due to line noise.
         */

        *ptr++ = END;

        /*
         * For each byte in the packet, send the appropriate
         * character sequence, according to the SLIP protocol.
         */

        while (len-- > 0) {
                switch (c = *s++) {
                case END:
                        *ptr++ = ESC;
                        *ptr++ = ESC_END;
                        break;
                case ESC:
                        *ptr++ = ESC;
                        *ptr++ = ESC_ESC;
                        break;
                default:
                        *ptr++ = c;
                        break;
                }
        }
        *ptr++ = END;
        return ptr - d;
}

static void slip_unesc(struct slip *sl, unsigned char s)
{

        switch (s) {
        case END:
#ifdef CONFIG_SLIP_SMART
                /* drop keeptest bit = VSV */
                if (test_bit(SLF_KEEPTEST, &sl->flags))
                        clear_bit(SLF_KEEPTEST, &sl->flags);
#endif

                if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
                    (sl->rcount > 2))
                        sl_bump(sl);
                clear_bit(SLF_ESCAPE, &sl->flags);
                sl->rcount = 0;
                return;

        case ESC:
                set_bit(SLF_ESCAPE, &sl->flags);
                return;
        case ESC_ESC:
                if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
                        s = ESC;
                break;
        case ESC_END:
                if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
                        s = END;
                break;
        }
        if (!test_bit(SLF_ERROR, &sl->flags))  {
                if (sl->rcount < sl->buffsize)  {
                        sl->rbuff[sl->rcount++] = s;
                        return;
                }
                sl->dev->stats.rx_over_errors++;
                set_bit(SLF_ERROR, &sl->flags);
        }
}


#ifdef CONFIG_SLIP_MODE_SLIP6
/************************************************************************
 *                       6 BIT SLIP ENCAPSULATION                       *
 ************************************************************************/

static int slip_esc6(unsigned char *s, unsigned char *d, int len)
{
        unsigned char *ptr = d;
        unsigned char c;
        int i;
        unsigned short v = 0;
        short bits = 0;

        /*
         * Send an initial END character to flush out any
         * data that may have accumulated in the receiver
         * due to line noise.
         */

        *ptr++ = 0x70;

        /*
         * Encode the packet into printable ascii characters
         */

        for (i = 0; i < len; ++i) {
                v = (v << 8) | s[i];
                bits += 8;
                while (bits >= 6) {
                        bits -= 6;
                        c = 0x30 + ((v >> bits) & 0x3F);
                        *ptr++ = c;
                }
        }
        if (bits) {
                c = 0x30 + ((v << (6 - bits)) & 0x3F);
                *ptr++ = c;
        }
        *ptr++ = 0x70;
        return ptr - d;
}

static void slip_unesc6(struct slip *sl, unsigned char s)
{
        unsigned char c;

        if (s == 0x70) {
#ifdef CONFIG_SLIP_SMART
                /* drop keeptest bit = VSV */
                if (test_bit(SLF_KEEPTEST, &sl->flags))
                        clear_bit(SLF_KEEPTEST, &sl->flags);
#endif

                if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
                    (sl->rcount > 2))
                        sl_bump(sl);
                sl->rcount = 0;
                sl->xbits = 0;
                sl->xdata = 0;
        } else if (s >= 0x30 && s < 0x70) {
                sl->xdata = (sl->xdata << 6) | ((s - 0x30) & 0x3F);
                sl->xbits += 6;
                if (sl->xbits >= 8) {
                        sl->xbits -= 8;
                        c = (unsigned char)(sl->xdata >> sl->xbits);
                        if (!test_bit(SLF_ERROR, &sl->flags))  {
                                if (sl->rcount < sl->buffsize)  {
                                        sl->rbuff[sl->rcount++] = c;
                                        return;
                                }
                                sl->dev->stats.rx_over_errors++;
                                set_bit(SLF_ERROR, &sl->flags);
                        }
                }
        }
}
#endif /* CONFIG_SLIP_MODE_SLIP6 */

/* Perform I/O control on an active SLIP channel. */
static int slip_ioctl(struct tty_struct *tty, unsigned int cmd,
                unsigned long arg)
{
        struct slip *sl = tty->disc_data;
        unsigned int tmp;
        int __user *p = (int __user *)arg;

        /* First make sure we're connected. */
        if (!sl || sl->magic != SLIP_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 SIOCGIFENCAP:
                if (put_user(sl->mode, p))
                        return -EFAULT;
                return 0;

        case SIOCSIFENCAP:
                if (get_user(tmp, p))
                        return -EFAULT;
#ifndef SL_INCLUDE_CSLIP
                if (tmp & (SL_MODE_CSLIP|SL_MODE_ADAPTIVE))
                        return -EINVAL;
#else
                if ((tmp & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) ==
                    (SL_MODE_ADAPTIVE | SL_MODE_CSLIP))
                        /* return -EINVAL; */
                        tmp &= ~SL_MODE_ADAPTIVE;
#endif
#ifndef CONFIG_SLIP_MODE_SLIP6
                if (tmp & SL_MODE_SLIP6)
                        return -EINVAL;
#endif
                sl->mode = tmp;
                sl->dev->type = ARPHRD_SLIP + sl->mode;
                return 0;

        case SIOCSIFHWADDR:
                return -EINVAL;

#ifdef CONFIG_SLIP_SMART
        /* VSV changes start here */
        case SIOCSKEEPALIVE:
                if (get_user(tmp, p))
                        return -EFAULT;
                if (tmp > 255) /* max for unchar */
                        return -EINVAL;

                spin_lock_bh(&sl->lock);
                if (!sl->tty) {
                        spin_unlock_bh(&sl->lock);
                        return -ENODEV;
                }
                sl->keepalive = (u8)tmp;
                if (sl->keepalive != 0) {
                        mod_timer(&sl->keepalive_timer,
                                        jiffies + sl->keepalive * HZ);
                        set_bit(SLF_KEEPTEST, &sl->flags);
                } else
                        del_timer(&sl->keepalive_timer);
                spin_unlock_bh(&sl->lock);
                return 0;

        case SIOCGKEEPALIVE:
                if (put_user(sl->keepalive, p))
                        return -EFAULT;
                return 0;

        case SIOCSOUTFILL:
                if (get_user(tmp, p))
                        return -EFAULT;
                if (tmp > 255) /* max for unchar */
                        return -EINVAL;
                spin_lock_bh(&sl->lock);
                if (!sl->tty) {
                        spin_unlock_bh(&sl->lock);
                        return -ENODEV;
                }
                sl->outfill = (u8)tmp;
                if (sl->outfill != 0) {
                        mod_timer(&sl->outfill_timer,
                                                jiffies + sl->outfill * HZ);
                        set_bit(SLF_OUTWAIT, &sl->flags);
                } else
                        del_timer(&sl->outfill_timer);
                spin_unlock_bh(&sl->lock);
                return 0;

        case SIOCGOUTFILL:
                if (put_user(sl->outfill, p))
                        return -EFAULT;
                return 0;
        /* VSV changes end */
#endif
        default:
                return tty_mode_ioctl(tty, cmd, arg);
        }
}

/* VSV changes start here */
#ifdef CONFIG_SLIP_SMART
/* function sl_siocdevprivate called from net/core/dev.c
   to allow get/set outfill/keepalive parameter
   by ifconfig                                 */

static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq,
                             void __user *data, int cmd)
{
        struct slip *sl = netdev_priv(dev);
        unsigned long *p = (unsigned long *)&rq->ifr_ifru;

        if (sl == NULL)         /* Allocation failed ?? */
                return -ENODEV;

        if (in_compat_syscall())
                return -EOPNOTSUPP;

        spin_lock_bh(&sl->lock);

        if (!sl->tty) {
                spin_unlock_bh(&sl->lock);
                return -ENODEV;
        }

        switch (cmd) {
        case SIOCSKEEPALIVE:
                /* max for unchar */
                if ((unsigned)*p > 255) {
                        spin_unlock_bh(&sl->lock);
                        return -EINVAL;
                }
                sl->keepalive = (u8)*p;
                if (sl->keepalive != 0) {
                        sl->keepalive_timer.expires =
                                                jiffies + sl->keepalive * HZ;
                        mod_timer(&sl->keepalive_timer,
                                                jiffies + sl->keepalive * HZ);
                        set_bit(SLF_KEEPTEST, &sl->flags);
                } else
                        del_timer(&sl->keepalive_timer);
                break;

        case SIOCGKEEPALIVE:
                *p = sl->keepalive;
                break;

        case SIOCSOUTFILL:
                if ((unsigned)*p > 255) { /* max for unchar */
                        spin_unlock_bh(&sl->lock);
                        return -EINVAL;
                }
                sl->outfill = (u8)*p;
                if (sl->outfill != 0) {
                        mod_timer(&sl->outfill_timer,
                                                jiffies + sl->outfill * HZ);
                        set_bit(SLF_OUTWAIT, &sl->flags);
                } else
                        del_timer(&sl->outfill_timer);
                break;

        case SIOCGOUTFILL:
                *p = sl->outfill;
                break;

        case SIOCSLEASE:
                /* Resolve race condition, when ioctl'ing hanged up
                   and opened by another process device.
                 */
                if (sl->tty != current->signal->tty &&
                                                sl->pid != current->pid) {
                        spin_unlock_bh(&sl->lock);
                        return -EPERM;
                }
                sl->leased = 0;
                if (*p)
                        sl->leased = 1;
                break;

        case SIOCGLEASE:
                *p = sl->leased;
        }
        spin_unlock_bh(&sl->lock);
        return 0;
}
#endif
/* VSV changes end */

static struct tty_ldisc_ops sl_ldisc = {
        .owner          = THIS_MODULE,
        .num            = N_SLIP,
        .name           = "slip",
        .open           = slip_open,
        .close          = slip_close,
        .hangup         = slip_hangup,
        .ioctl          = slip_ioctl,
        .receive_buf    = slip_receive_buf,
        .write_wakeup   = slip_write_wakeup,
};

static int __init slip_init(void)
{
        int status;

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

        printk(KERN_INFO "SLIP: version %s (dynamic channels, max=%d)"
#ifdef CONFIG_SLIP_MODE_SLIP6
               " (6 bit encapsulation enabled)"
#endif
               ".\n",
               SLIP_VERSION, slip_maxdev);
#if defined(SL_INCLUDE_CSLIP)
        printk(KERN_INFO "CSLIP: code copyright 1989 Regents of the University of California.\n");
#endif
#ifdef CONFIG_SLIP_SMART
        printk(KERN_INFO "SLIP linefill/keepalive option.\n");
#endif

        slip_devs = kcalloc(slip_maxdev, sizeof(struct net_device *),
                                                                GFP_KERNEL);
        if (!slip_devs)
                return -ENOMEM;

        /* Fill in our line protocol discipline, and register it */
        status = tty_register_ldisc(&sl_ldisc);
        if (status != 0) {
                printk(KERN_ERR "SLIP: can't register line discipline (err = %d)\n", status);
                kfree(slip_devs);
        }
        return status;
}

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

        if (slip_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 < slip_maxdev; i++) {
                        dev = slip_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 < slip_maxdev; i++) {
                dev = slip_devs[i];
                if (!dev)
                        continue;
                slip_devs[i] = NULL;

                sl = netdev_priv(dev);
                if (sl->tty) {
                        printk(KERN_ERR "%s: tty discipline still running\n",
                               dev->name);
                }

                unregister_netdev(dev);
        }

        kfree(slip_devs);
        slip_devs = NULL;

        tty_unregister_ldisc(&sl_ldisc);
}

module_init(slip_init);
module_exit(slip_exit);

#ifdef CONFIG_SLIP_SMART
/*
 * This is start of the code for multislip style line checking
 * added by Stanislav Voronyi. All changes before marked VSV
 */

static void sl_outfill(struct timer_list *t)
{
        struct slip *sl = from_timer(sl, t, outfill_timer);

        spin_lock(&sl->lock);

        if (sl->tty == NULL)
                goto out;

        if (sl->outfill) {
                if (test_bit(SLF_OUTWAIT, &sl->flags)) {
                        /* no packets were transmitted, do outfill */
#ifdef CONFIG_SLIP_MODE_SLIP6
                        unsigned char s = (sl->mode & SL_MODE_SLIP6)?0x70:END;
#else
                        unsigned char s = END;
#endif
                        /* put END into tty queue. Is it right ??? */
                        if (!netif_queue_stopped(sl->dev)) {
                                /* if device busy no outfill */
                                sl->tty->ops->write(sl->tty, &s, 1);
                        }
                } else
                        set_bit(SLF_OUTWAIT, &sl->flags);

                mod_timer(&sl->outfill_timer, jiffies+sl->outfill*HZ);
        }
out:
        spin_unlock(&sl->lock);
}

static void sl_keepalive(struct timer_list *t)
{
        struct slip *sl = from_timer(sl, t, keepalive_timer);

        spin_lock(&sl->lock);

        if (sl->tty == NULL)
                goto out;

        if (sl->keepalive) {
                if (test_bit(SLF_KEEPTEST, &sl->flags)) {
                        /* keepalive still high :(, we must hangup */
                        if (sl->outfill)
                                /* outfill timer must be deleted too */
                                (void)del_timer(&sl->outfill_timer);
                        printk(KERN_DEBUG "%s: no packets received during keepalive timeout, hangup.\n", sl->dev->name);
                        /* this must hangup tty & close slip */
                        tty_hangup(sl->tty);
                        /* I think we need not something else */
                        goto out;
                } else
                        set_bit(SLF_KEEPTEST, &sl->flags);

                mod_timer(&sl->keepalive_timer, jiffies+sl->keepalive*HZ);
        }
out:
        spin_unlock(&sl->lock);
}

#endif
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_SLIP);