slip.c

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/*
 * 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, <[email protected]>
 *      Fred N. van Kempen, <[email protected]>
 *
 * 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 <[email protected]>
 *                  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/module.h>
#include <linux/moduleparam.h>

#include <asm/uaccess.h>
#include <linux/bitops.h>
#include <linux/sched.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/compat.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/slab.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(unsigned long sls);
static void sl_outfill(unsigned long sls);
static int sl_ioctl(struct net_device *dev, struct ifreq *rq, 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 (slcomp == NULL)
        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;
    memcpy(skb_put(skb, count), 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
    sl->dev->trans_start = jiffies;
#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
}

/*
 * Called by the driver when there's room for more data.  If we have
 * more packets to send, we send them here.
 */
static void slip_write_wakeup(struct tty_struct *tty)
{
    int actual;
    struct slip *sl = tty->disc_data;

    /* First make sure we're connected. */
    if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
        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, &tty->flags);
        sl_unlock(sl);
        return;
    }

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

static void sl_tx_timeout(struct net_device *dev)
{
    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);

    if (new_mtu < 68 || new_mtu > 65534)
        return -EINVAL;

    if (new_mtu != dev->mtu)
        return sl_realloc_bufs(sl, new_mtu);
    return 0;
}

/* Netdevice get statistics request */

static struct rtnl_link_stats64 *
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
    return stats;
}

/* 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;
    free_netdev(dev);
    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_do_ioctl       = sl_ioctl,
#endif
};


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

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

    /* 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,
                            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(dev_t line)
{
    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, 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);
    sl->mode        = SL_MODE_DEFAULT;
#ifdef CONFIG_SLIP_SMART
    /* initialize timer_list struct */
    init_timer(&sl->keepalive_timer);
    sl->keepalive_timer.data = (unsigned long)sl;
    sl->keepalive_timer.function = sl_keepalive;
    init_timer(&sl->outfill_timer);
    sl->outfill_timer.data = (unsigned long)sl;
    sl->outfill_timer.function = sl_outfill;
#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(tty_devnum(tty));
    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);

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;

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

    /* 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 int slip_hangup(struct tty_struct *tty)
{
    slip_close(tty);
    return 0;
}
 /************************************************************************
  *         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, struct file *file,
                    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, file, cmd, arg);
    }
}

#ifdef CONFIG_COMPAT
static long slip_compat_ioctl(struct tty_struct *tty, struct file *file,
                    unsigned int cmd, unsigned long arg)
{
    switch (cmd) {
    case SIOCGIFNAME:
    case SIOCGIFENCAP:
    case SIOCSIFENCAP:
    case SIOCSIFHWADDR:
    case SIOCSKEEPALIVE:
    case SIOCGKEEPALIVE:
    case SIOCSOUTFILL:
    case SIOCGOUTFILL:
        return slip_ioctl(tty, file, cmd,
                  (unsigned long)compat_ptr(arg));
    }

    return -ENOIOCTLCMD;
}
#endif

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

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

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

    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,
    .magic      = TTY_LDISC_MAGIC,
    .name       = "slip",
    .open       = slip_open,
    .close      = slip_close,
    .hangup     = slip_hangup,
    .ioctl      = slip_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = slip_compat_ioctl,
#endif
    .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 = kzalloc(sizeof(struct net_device *)*slip_maxdev,
                                GFP_KERNEL);
    if (!slip_devs)
        return -ENOMEM;

    /* Fill in our line protocol discipline, and register it */
    status = tty_register_ldisc(N_SLIP, &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);
            /* Intentionally leak the control block. */
            dev->destructor = NULL;
        }

        unregister_netdev(dev);
    }

    kfree(slip_devs);
    slip_devs = NULL;

    i = tty_unregister_ldisc(N_SLIP);
    if (i != 0)
        printk(KERN_ERR "SLIP: can't unregister line discipline (err = %d)\n", i);
}

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(unsigned long sls)
{
    struct slip *sl = (struct slip *)sls;

    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(unsigned long sls)
{
    struct slip *sl = (struct slip *)sls;

    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);