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mkiss.c

/*
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License (Version 2) as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope 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, write to the Free Software Foundation, Inc.,
 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * Copyright (C) Hans Alblas PE1AYX <hans@esrac.ele.tue.nl>
 * Copyright (C) 2004, 05 Ralf Baechle DL5RB <ralf@linux-mips.org>
 * Copyright (C) 2004, 05 Thomas Osterried DL9SAU <thomas@x-berg.in-berlin.de>
 */
#include <linux/module.h>
#include <asm/system.h>
#include <linux/bitops.h>
#include <asm/uaccess.h>
#include <linux/crc16.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/major.h>
#include <linux/init.h>
#include <linux/rtnetlink.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
#include <linux/jiffies.h>

#include <net/ax25.h>

#define AX_MTU          236

/* SLIP/KISS protocol characters. */
#define END             0300        /* indicates end of frame     */
#define ESC             0333        /* indicates byte stuffing    */
#define ESC_END         0334        /* ESC ESC_END means END 'data'     */
#define ESC_ESC         0335        /* ESC ESC_ESC means ESC 'data'     */

struct mkiss {
      struct tty_struct *tty; /* ptr to TTY structure       */
      struct net_device *dev; /* easy for intr handling     */

      /* These are pointers to the malloc()ed frame buffers. */
      spinlock_t        buflock;/* lock for rbuf and xbuf */
      unsigned char           *rbuff;     /* receiver buffer            */
      int               rcount;     /* received chars counter       */
      unsigned char           *xbuff;     /* transmitter buffer         */
      unsigned char           *xhead;     /* pointer to next byte to XMIT */
      int               xleft;      /* bytes left in XMIT queue     */

      struct net_device_stats stats;

      /* Detailed SLIP statistics. */
      int         mtu;        /* Our mtu (to spot changes!)   */
      int         buffsize;   /* Max buffers sizes            */

      unsigned long     flags;            /* Flag values/ mode etc      */
                              /* long req'd: used by set_bit --RR */
#define AXF_INUSE 0           /* Channel in use               */
#define AXF_ESCAPE      1               /* ESC received                 */
#define AXF_ERROR 2               /* Parity, etc. error           */
#define AXF_KEEPTEST    3           /* Keepalive test flag        */
#define AXF_OUTWAIT     4           /* is outpacket was flag      */

      int         mode;
        int       crcmode;    /* MW: for FlexNet, SMACK etc.  */
      int         crcauto;    /* CRC auto mode */

#define CRC_MODE_NONE         0
#define CRC_MODE_FLEX         1
#define CRC_MODE_SMACK        2
#define CRC_MODE_FLEX_TEST    3
#define CRC_MODE_SMACK_TEST   4

      atomic_t          refcnt;
      struct semaphore  dead_sem;
};

/*---------------------------------------------------------------------------*/

static const unsigned short crc_flex_table[] = {
      0x0f87, 0x1e0e, 0x2c95, 0x3d1c, 0x49a3, 0x582a, 0x6ab1, 0x7b38,
      0x83cf, 0x9246, 0xa0dd, 0xb154, 0xc5eb, 0xd462, 0xe6f9, 0xf770,
      0x1f06, 0x0e8f, 0x3c14, 0x2d9d, 0x5922, 0x48ab, 0x7a30, 0x6bb9,
      0x934e, 0x82c7, 0xb05c, 0xa1d5, 0xd56a, 0xc4e3, 0xf678, 0xe7f1,
      0x2e85, 0x3f0c, 0x0d97, 0x1c1e, 0x68a1, 0x7928, 0x4bb3, 0x5a3a,
      0xa2cd, 0xb344, 0x81df, 0x9056, 0xe4e9, 0xf560, 0xc7fb, 0xd672,
      0x3e04, 0x2f8d, 0x1d16, 0x0c9f, 0x7820, 0x69a9, 0x5b32, 0x4abb,
      0xb24c, 0xa3c5, 0x915e, 0x80d7, 0xf468, 0xe5e1, 0xd77a, 0xc6f3,
      0x4d83, 0x5c0a, 0x6e91, 0x7f18, 0x0ba7, 0x1a2e, 0x28b5, 0x393c,
      0xc1cb, 0xd042, 0xe2d9, 0xf350, 0x87ef, 0x9666, 0xa4fd, 0xb574,
      0x5d02, 0x4c8b, 0x7e10, 0x6f99, 0x1b26, 0x0aaf, 0x3834, 0x29bd,
      0xd14a, 0xc0c3, 0xf258, 0xe3d1, 0x976e, 0x86e7, 0xb47c, 0xa5f5,
      0x6c81, 0x7d08, 0x4f93, 0x5e1a, 0x2aa5, 0x3b2c, 0x09b7, 0x183e,
      0xe0c9, 0xf140, 0xc3db, 0xd252, 0xa6ed, 0xb764, 0x85ff, 0x9476,
      0x7c00, 0x6d89, 0x5f12, 0x4e9b, 0x3a24, 0x2bad, 0x1936, 0x08bf,
      0xf048, 0xe1c1, 0xd35a, 0xc2d3, 0xb66c, 0xa7e5, 0x957e, 0x84f7,
      0x8b8f, 0x9a06, 0xa89d, 0xb914, 0xcdab, 0xdc22, 0xeeb9, 0xff30,
      0x07c7, 0x164e, 0x24d5, 0x355c, 0x41e3, 0x506a, 0x62f1, 0x7378,
      0x9b0e, 0x8a87, 0xb81c, 0xa995, 0xdd2a, 0xcca3, 0xfe38, 0xefb1,
      0x1746, 0x06cf, 0x3454, 0x25dd, 0x5162, 0x40eb, 0x7270, 0x63f9,
      0xaa8d, 0xbb04, 0x899f, 0x9816, 0xeca9, 0xfd20, 0xcfbb, 0xde32,
      0x26c5, 0x374c, 0x05d7, 0x145e, 0x60e1, 0x7168, 0x43f3, 0x527a,
      0xba0c, 0xab85, 0x991e, 0x8897, 0xfc28, 0xeda1, 0xdf3a, 0xceb3,
      0x3644, 0x27cd, 0x1556, 0x04df, 0x7060, 0x61e9, 0x5372, 0x42fb,
      0xc98b, 0xd802, 0xea99, 0xfb10, 0x8faf, 0x9e26, 0xacbd, 0xbd34,
      0x45c3, 0x544a, 0x66d1, 0x7758, 0x03e7, 0x126e, 0x20f5, 0x317c,
      0xd90a, 0xc883, 0xfa18, 0xeb91, 0x9f2e, 0x8ea7, 0xbc3c, 0xadb5,
      0x5542, 0x44cb, 0x7650, 0x67d9, 0x1366, 0x02ef, 0x3074, 0x21fd,
      0xe889, 0xf900, 0xcb9b, 0xda12, 0xaead, 0xbf24, 0x8dbf, 0x9c36,
      0x64c1, 0x7548, 0x47d3, 0x565a, 0x22e5, 0x336c, 0x01f7, 0x107e,
      0xf808, 0xe981, 0xdb1a, 0xca93, 0xbe2c, 0xafa5, 0x9d3e, 0x8cb7,
      0x7440, 0x65c9, 0x5752, 0x46db, 0x3264, 0x23ed, 0x1176, 0x00ff
};

static unsigned short calc_crc_flex(unsigned char *cp, int size)
{
      unsigned short crc = 0xffff;

      while (size--)
            crc = (crc << 8) ^ crc_flex_table[((crc >> 8) ^ *cp++) & 0xff];

      return crc;
}

static int check_crc_flex(unsigned char *cp, int size)
{
      unsigned short crc = 0xffff;

      if (size < 3)
            return -1;

      while (size--)
            crc = (crc << 8) ^ crc_flex_table[((crc >> 8) ^ *cp++) & 0xff];

      if ((crc & 0xffff) != 0x7070)
            return -1;

      return 0;
}

static int check_crc_16(unsigned char *cp, int size)
{
      unsigned short crc = 0x0000;

      if (size < 3)
            return -1;

      crc = crc16(0, cp, size);

      if (crc != 0x0000)
            return -1;

      return 0;
}

/*
 * Standard encapsulation
 */

static int kiss_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;

      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;
}

/*
 * MW:
 * OK its ugly, but tell me a better solution without copying the
 * packet to a temporary buffer :-)
 */
static int kiss_esc_crc(unsigned char *s, unsigned char *d, unsigned short crc,
      int len)
{
      unsigned char *ptr = d;
      unsigned char c=0;

      *ptr++ = END;
      while (len > 0) {
            if (len > 2)
                  c = *s++;
            else if (len > 1)
                  c = crc >> 8;
            else if (len > 0)
                  c = crc & 0xff;

            len--;

            switch (c) {
            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;
}

/* Send one completely decapsulated AX.25 packet to the AX.25 layer. */
static void ax_bump(struct mkiss *ax)
{
      struct sk_buff *skb;
      int count;

      spin_lock_bh(&ax->buflock);
      if (ax->rbuff[0] > 0x0f) {
            if (ax->rbuff[0] & 0x80) {
                  if (check_crc_16(ax->rbuff, ax->rcount) < 0) {
                        ax->stats.rx_errors++;
                        spin_unlock_bh(&ax->buflock);

                        return;
                  }
                  if (ax->crcmode != CRC_MODE_SMACK && ax->crcauto) {
                        printk(KERN_INFO
                               "mkiss: %s: Switchting to crc-smack\n",
                               ax->dev->name);
                        ax->crcmode = CRC_MODE_SMACK;
                  }
                  ax->rcount -= 2;
                  *ax->rbuff &= ~0x80;
            } else if (ax->rbuff[0] & 0x20)  {
                  if (check_crc_flex(ax->rbuff, ax->rcount) < 0) {
                        ax->stats.rx_errors++;
                        spin_unlock_bh(&ax->buflock);
                        return;
                  }
                  if (ax->crcmode != CRC_MODE_FLEX && ax->crcauto) {
                        printk(KERN_INFO
                               "mkiss: %s: Switchting to crc-flexnet\n",
                               ax->dev->name);
                        ax->crcmode = CRC_MODE_FLEX;
                  }
                  ax->rcount -= 2;

                  /*
                   * dl9sau bugfix: the trailling two bytes flexnet crc
                   * will not be passed to the kernel. thus we have to
                   * correct the kissparm signature, because it indicates
                   * a crc but there's none
                   */
                  *ax->rbuff &= ~0x20;
            }
      }
      spin_unlock_bh(&ax->buflock);

      count = ax->rcount;

      if ((skb = dev_alloc_skb(count)) == NULL) {
            printk(KERN_ERR "mkiss: %s: memory squeeze, dropping packet.\n",
                   ax->dev->name);
            ax->stats.rx_dropped++;
            return;
      }

      spin_lock_bh(&ax->buflock);
      memcpy(skb_put(skb,count), ax->rbuff, count);
      spin_unlock_bh(&ax->buflock);
      skb->protocol = ax25_type_trans(skb, ax->dev);
      netif_rx(skb);
      ax->dev->last_rx = jiffies;
      ax->stats.rx_packets++;
      ax->stats.rx_bytes += count;
}

static void kiss_unesc(struct mkiss *ax, unsigned char s)
{
      switch (s) {
      case END:
            /* drop keeptest bit = VSV */
            if (test_bit(AXF_KEEPTEST, &ax->flags))
                  clear_bit(AXF_KEEPTEST, &ax->flags);

            if (!test_and_clear_bit(AXF_ERROR, &ax->flags) && (ax->rcount > 2))
                  ax_bump(ax);

            clear_bit(AXF_ESCAPE, &ax->flags);
            ax->rcount = 0;
            return;

      case ESC:
            set_bit(AXF_ESCAPE, &ax->flags);
            return;
      case ESC_ESC:
            if (test_and_clear_bit(AXF_ESCAPE, &ax->flags))
                  s = ESC;
            break;
      case ESC_END:
            if (test_and_clear_bit(AXF_ESCAPE, &ax->flags))
                  s = END;
            break;
      }

      spin_lock_bh(&ax->buflock);
      if (!test_bit(AXF_ERROR, &ax->flags)) {
            if (ax->rcount < ax->buffsize) {
                  ax->rbuff[ax->rcount++] = s;
                  spin_unlock_bh(&ax->buflock);
                  return;
            }

            ax->stats.rx_over_errors++;
            set_bit(AXF_ERROR, &ax->flags);
      }
      spin_unlock_bh(&ax->buflock);
}

static int ax_set_mac_address(struct net_device *dev, void *addr)
{
      struct sockaddr_ax25 *sa = addr;

      netif_tx_lock_bh(dev);
      memcpy(dev->dev_addr, &sa->sax25_call, AX25_ADDR_LEN);
      netif_tx_unlock_bh(dev);

      return 0;
}

/*---------------------------------------------------------------------------*/

static void ax_changedmtu(struct mkiss *ax)
{
      struct net_device *dev = ax->dev;
      unsigned char *xbuff, *rbuff, *oxbuff, *orbuff;
      int len;

      len = dev->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);

      if (xbuff == NULL || rbuff == NULL)  {
            printk(KERN_ERR "mkiss: %s: unable to grow ax25 buffers, "
                   "MTU change cancelled.\n",
                   ax->dev->name);
            dev->mtu = ax->mtu;
            kfree(xbuff);
            kfree(rbuff);
            return;
      }

      spin_lock_bh(&ax->buflock);

      oxbuff    = ax->xbuff;
      ax->xbuff = xbuff;
      orbuff    = ax->rbuff;
      ax->rbuff = rbuff;

      if (ax->xleft) {
            if (ax->xleft <= len) {
                  memcpy(ax->xbuff, ax->xhead, ax->xleft);
            } else  {
                  ax->xleft = 0;
                  ax->stats.tx_dropped++;
            }
      }

      ax->xhead = ax->xbuff;

      if (ax->rcount) {
            if (ax->rcount <= len) {
                  memcpy(ax->rbuff, orbuff, ax->rcount);
            } else  {
                  ax->rcount = 0;
                  ax->stats.rx_over_errors++;
                  set_bit(AXF_ERROR, &ax->flags);
            }
      }

      ax->mtu      = dev->mtu + 73;
      ax->buffsize = len;

      spin_unlock_bh(&ax->buflock);

      kfree(oxbuff);
      kfree(orbuff);
}

/* Encapsulate one AX.25 packet and stuff into a TTY queue. */
static void ax_encaps(struct net_device *dev, unsigned char *icp, int len)
{
      struct mkiss *ax = netdev_priv(dev);
      unsigned char *p;
      int actual, count;

      if (ax->mtu != ax->dev->mtu + 73)   /* Someone has been ifconfigging */
            ax_changedmtu(ax);

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

      p = icp;

      spin_lock_bh(&ax->buflock);
      if ((*p & 0x0f) != 0) {
            /* Configuration Command (kissparms(1).
             * Protocol spec says: never append CRC.
             * This fixes a very old bug in the linux
             * kiss driver. -- dl9sau */
            switch (*p & 0xff) {
            case 0x85:
                  /* command from userspace especially for us,
                   * not for delivery to the tnc */
                  if (len > 1) {
                        int cmd = (p[1] & 0xff);
                        switch(cmd) {
                        case 3:
                          ax->crcmode = CRC_MODE_SMACK;
                          break;
                        case 2:
                          ax->crcmode = CRC_MODE_FLEX;
                          break;
                        case 1:
                          ax->crcmode = CRC_MODE_NONE;
                          break;
                        case 0:
                        default:
                          ax->crcmode = CRC_MODE_SMACK_TEST;
                          cmd = 0;
                        }
                        ax->crcauto = (cmd ? 0 : 1);
                        printk(KERN_INFO "mkiss: %s: crc mode %s %d\n", ax->dev->name, (len) ? "set to" : "is", cmd);
                  }
                  spin_unlock_bh(&ax->buflock);
                  netif_start_queue(dev);

                  return;
            default:
                  count = kiss_esc(p, (unsigned char *)ax->xbuff, len);
            }
      } else {
            unsigned short crc;
            switch (ax->crcmode) {
            case CRC_MODE_SMACK_TEST:
                  ax->crcmode  = CRC_MODE_FLEX_TEST;
                  printk(KERN_INFO "mkiss: %s: Trying crc-smack\n", ax->dev->name);
                  // fall through
            case CRC_MODE_SMACK:
                  *p |= 0x80;
                  crc = swab16(crc16(0, p, len));
                  count = kiss_esc_crc(p, (unsigned char *)ax->xbuff, crc, len+2);
                  break;
            case CRC_MODE_FLEX_TEST:
                  ax->crcmode = CRC_MODE_NONE;
                  printk(KERN_INFO "mkiss: %s: Trying crc-flexnet\n", ax->dev->name);
                  // fall through
            case CRC_MODE_FLEX:
                  *p |= 0x20;
                  crc = calc_crc_flex(p, len);
                  count = kiss_esc_crc(p, (unsigned char *)ax->xbuff, crc, len+2);
                  break;

            default:
                  count = kiss_esc(p, (unsigned char *)ax->xbuff, len);
            }
      }
      spin_unlock_bh(&ax->buflock);

      set_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags);
      actual = ax->tty->driver->write(ax->tty, ax->xbuff, count);
      ax->stats.tx_packets++;
      ax->stats.tx_bytes += actual;

      ax->dev->trans_start = jiffies;
      ax->xleft = count - actual;
      ax->xhead = ax->xbuff + actual;
}

/* Encapsulate an AX.25 packet and kick it into a TTY queue. */
static int ax_xmit(struct sk_buff *skb, struct net_device *dev)
{
      struct mkiss *ax = netdev_priv(dev);

      if (!netif_running(dev))  {
            printk(KERN_ERR "mkiss: %s: xmit call when iface is down\n", dev->name);
            return 1;
      }

      if (netif_queue_stopped(dev)) {
            /*
             * May be we must check transmitter timeout here ?
             *      14 Oct 1994 Dmitry Gorodchanin.
             */
            if (time_before(jiffies, dev->trans_start + 20 * HZ)) {
                  /* 20 sec timeout not reached */
                  return 1;
            }

            printk(KERN_ERR "mkiss: %s: transmit timed out, %s?\n", dev->name,
                   (ax->tty->driver->chars_in_buffer(ax->tty) || ax->xleft) ?
                   "bad line quality" : "driver error");

            ax->xleft = 0;
            clear_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags);
            netif_start_queue(dev);
      }

      /* We were not busy, so we are now... :-) */
      if (skb != NULL) {
            netif_stop_queue(dev);
            ax_encaps(dev, skb->data, skb->len);
            kfree_skb(skb);
      }

      return 0;
}

static int ax_open_dev(struct net_device *dev)
{
      struct mkiss *ax = netdev_priv(dev);

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

      return 0;
}

#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)

/* Return the frame type ID */
static int ax_header(struct sk_buff *skb, struct net_device *dev,
                 unsigned short type, const void *daddr,
                 const void *saddr, unsigned len)
{
#ifdef CONFIG_INET
      if (type != ETH_P_AX25)
            return ax25_hard_header(skb, dev, type, daddr, saddr, len);
#endif
      return 0;
}


static int ax_rebuild_header(struct sk_buff *skb)
{
#ifdef CONFIG_INET
      return ax25_rebuild_header(skb);
#else
      return 0;
#endif
}

#endif      /* CONFIG_{AX25,AX25_MODULE} */

/* Open the low-level part of the AX25 channel. Easy! */
static int ax_open(struct net_device *dev)
{
      struct mkiss *ax = netdev_priv(dev);
      unsigned long len;

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

      /*
       * Allocate the frame buffers:
       *
       * rbuff    Receive buffer.
       * xbuff    Transmit buffer.
       */
      len = dev->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;

      if ((ax->rbuff = kmalloc(len + 4, GFP_KERNEL)) == NULL)
            goto norbuff;

      if ((ax->xbuff = kmalloc(len + 4, GFP_KERNEL)) == NULL)
            goto noxbuff;

      ax->mtu          = dev->mtu + 73;
      ax->buffsize = len;
      ax->rcount   = 0;
      ax->xleft    = 0;

      ax->flags   &= (1 << AXF_INUSE);      /* Clear ESCAPE & ERROR flags */

      spin_lock_init(&ax->buflock);

      return 0;

noxbuff:
      kfree(ax->rbuff);

norbuff:
      return -ENOMEM;
}


/* Close the low-level part of the AX25 channel. Easy! */
static int ax_close(struct net_device *dev)
{
      struct mkiss *ax = netdev_priv(dev);

      if (ax->tty)
            clear_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags);

      netif_stop_queue(dev);

      return 0;
}

static struct net_device_stats *ax_get_stats(struct net_device *dev)
{
      struct mkiss *ax = netdev_priv(dev);

      return &ax->stats;
}

static const struct header_ops ax_header_ops = {
      .create    = ax_header,
      .rebuild   = ax_rebuild_header,
};

static void ax_setup(struct net_device *dev)
{
      /* Finish setting up the DEVICE info. */
      dev->mtu             = AX_MTU;
      dev->hard_start_xmit = ax_xmit;
      dev->open            = ax_open_dev;
      dev->stop            = ax_close;
      dev->get_stats         = ax_get_stats;
      dev->set_mac_address = ax_set_mac_address;
      dev->hard_header_len = 0;
      dev->addr_len        = 0;
      dev->type            = ARPHRD_AX25;
      dev->tx_queue_len    = 10;
      dev->header_ops      = &ax_header_ops;


      memcpy(dev->broadcast, &ax25_bcast, AX25_ADDR_LEN);
      memcpy(dev->dev_addr,  &ax25_defaddr,  AX25_ADDR_LEN);

      dev->flags      = IFF_BROADCAST | IFF_MULTICAST;
}

/*
 * We have a potential race on dereferencing tty->disc_data, because the tty
 * layer provides no locking at all - thus one cpu could be running
 * sixpack_receive_buf while another calls sixpack_close, which zeroes
 * tty->disc_data and frees the memory that sixpack_receive_buf is using.  The
 * best way to fix this is to use a rwlock in the tty struct, but for now we
 * use a single global rwlock for all ttys in ppp line discipline.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct mkiss *mkiss_get(struct tty_struct *tty)
{
      struct mkiss *ax;

      read_lock(&disc_data_lock);
      ax = tty->disc_data;
      if (ax)
            atomic_inc(&ax->refcnt);
      read_unlock(&disc_data_lock);

      return ax;
}

static void mkiss_put(struct mkiss *ax)
{
      if (atomic_dec_and_test(&ax->refcnt))
            up(&ax->dead_sem);
}

static int crc_force = 0;     /* Can be overridden with insmod */

static int mkiss_open(struct tty_struct *tty)
{
      struct net_device *dev;
      struct mkiss *ax;
      int err;

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

      dev = alloc_netdev(sizeof(struct mkiss), "ax%d", ax_setup);
      if (!dev) {
            err = -ENOMEM;
            goto out;
      }

      ax = netdev_priv(dev);
      ax->dev = dev;

      spin_lock_init(&ax->buflock);
      atomic_set(&ax->refcnt, 1);
      init_MUTEX_LOCKED(&ax->dead_sem);

      ax->tty = tty;
      tty->disc_data = ax;
      tty->receive_room = 65535;

      if (tty->driver->flush_buffer)
            tty->driver->flush_buffer(tty);

      /* Restore default settings */
      dev->type = ARPHRD_AX25;

      /* Perform the low-level AX25 initialization. */
      if ((err = ax_open(ax->dev))) {
            goto out_free_netdev;
      }

      if (register_netdev(dev))
            goto out_free_buffers;

      /* after register_netdev() - because else printk smashes the kernel */
      switch (crc_force) {
      case 3:
            ax->crcmode  = CRC_MODE_SMACK;
            printk(KERN_INFO "mkiss: %s: crc mode smack forced.\n",
                   ax->dev->name);
            break;
      case 2:
            ax->crcmode  = CRC_MODE_FLEX;
            printk(KERN_INFO "mkiss: %s: crc mode flexnet forced.\n",
                   ax->dev->name);
            break;
      case 1:
            ax->crcmode  = CRC_MODE_NONE;
            printk(KERN_INFO "mkiss: %s: crc mode disabled.\n",
                   ax->dev->name);
            break;
      case 0:
            /* fall through */
      default:
            crc_force = 0;
            printk(KERN_INFO "mkiss: %s: crc mode is auto.\n",
                   ax->dev->name);
            ax->crcmode  = CRC_MODE_SMACK_TEST;
      }
      ax->crcauto = (crc_force ? 0 : 1);

      netif_start_queue(dev);

      /* Done.  We have linked the TTY line to a channel. */
      return 0;

out_free_buffers:
      kfree(ax->rbuff);
      kfree(ax->xbuff);

out_free_netdev:
      free_netdev(dev);

out:
      return err;
}

static void mkiss_close(struct tty_struct *tty)
{
      struct mkiss *ax;

      write_lock(&disc_data_lock);
      ax = tty->disc_data;
      tty->disc_data = NULL;
      write_unlock(&disc_data_lock);

      if (ax == 0)
            return;

      /*
       * We have now ensured that nobody can start using ap from now on, but
       * we have to wait for all existing users to finish.
       */
      if (!atomic_dec_and_test(&ax->refcnt))
            down(&ax->dead_sem);

      unregister_netdev(ax->dev);

      /* Free all AX25 frame buffers. */
      kfree(ax->rbuff);
      kfree(ax->xbuff);

      ax->tty = NULL;
}

/* Perform I/O control on an active ax25 channel. */
static int mkiss_ioctl(struct tty_struct *tty, struct file *file,
      unsigned int cmd, unsigned long arg)
{
      struct mkiss *ax = mkiss_get(tty);
      struct net_device *dev = ax->dev;
      unsigned int tmp, err;

      /* First make sure we're connected. */
      if (ax == NULL)
            return -ENXIO;

      switch (cmd) {
      case SIOCGIFNAME:
            err = copy_to_user((void __user *) arg, ax->dev->name,
                               strlen(ax->dev->name) + 1) ? -EFAULT : 0;
            break;

      case SIOCGIFENCAP:
            err = put_user(4, (int __user *) arg);
            break;

      case SIOCSIFENCAP:
            if (get_user(tmp, (int __user *) arg)) {
                  err = -EFAULT;
                  break;
            }

            ax->mode = tmp;
            dev->addr_len        = AX25_ADDR_LEN;
            dev->hard_header_len = AX25_KISS_HEADER_LEN +
                                   AX25_MAX_HEADER_LEN + 3;
            dev->type            = ARPHRD_AX25;

            err = 0;
            break;

      case SIOCSIFHWADDR: {
            char addr[AX25_ADDR_LEN];

            if (copy_from_user(&addr,
                               (void __user *) arg, AX25_ADDR_LEN)) {
                  err = -EFAULT;
                  break;
            }

            netif_tx_lock_bh(dev);
            memcpy(dev->dev_addr, addr, AX25_ADDR_LEN);
            netif_tx_unlock_bh(dev);

            err = 0;
            break;
      }
      default:
            err = -ENOIOCTLCMD;
      }

      mkiss_put(ax);

      return err;
}

/*
 * Handle the 'receiver data ready' interrupt.
 * This function is called by the 'tty_io' module in the kernel when
 * a block of data has been received, which can now be decapsulated
 * and sent on to the AX.25 layer for further processing.
 */
static void mkiss_receive_buf(struct tty_struct *tty, const unsigned char *cp,
      char *fp, int count)
{
      struct mkiss *ax = mkiss_get(tty);

      if (!ax)
            return;

      /*
       * Argh! mtu change time! - costs us the packet part received
       * at the change
       */
      if (ax->mtu != ax->dev->mtu + 73)
            ax_changedmtu(ax);

      /* Read the characters out of the buffer */
      while (count--) {
            if (fp != NULL && *fp++) {
                  if (!test_and_set_bit(AXF_ERROR, &ax->flags))
                        ax->stats.rx_errors++;
                  cp++;
                  continue;
            }

            kiss_unesc(ax, *cp++);
      }

      mkiss_put(ax);
      if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
          && tty->driver->unthrottle)
            tty->driver->unthrottle(tty);
}

/*
 * Called by the driver when there's room for more data.  If we have
 * more packets to send, we send them here.
 */
static void mkiss_write_wakeup(struct tty_struct *tty)
{
      struct mkiss *ax = mkiss_get(tty);
      int actual;

      if (!ax)
            return;

      if (ax->xleft <= 0)  {
            /* Now serial buffer is almost free & we can start
             * transmission of another packet
             */
            clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);

            netif_wake_queue(ax->dev);
            goto out;
      }

      actual = tty->driver->write(tty, ax->xhead, ax->xleft);
      ax->xleft -= actual;
      ax->xhead += actual;

out:
      mkiss_put(ax);
}

static struct tty_ldisc ax_ldisc = {
      .owner            = THIS_MODULE,
      .magic            = TTY_LDISC_MAGIC,
      .name       = "mkiss",
      .open       = mkiss_open,
      .close            = mkiss_close,
      .ioctl            = mkiss_ioctl,
      .receive_buf      = mkiss_receive_buf,
      .write_wakeup     = mkiss_write_wakeup
};

static char banner[] __initdata = KERN_INFO \
      "mkiss: AX.25 Multikiss, Hans Albas PE1AYX\n";
static char msg_regfail[] __initdata = KERN_ERR \
      "mkiss: can't register line discipline (err = %d)\n";

static int __init mkiss_init_driver(void)
{
      int status;

      printk(banner);

      if ((status = tty_register_ldisc(N_AX25, &ax_ldisc)) != 0)
            printk(msg_regfail);

      return status;
}

static const char msg_unregfail[] __exitdata = KERN_ERR \
      "mkiss: can't unregister line discipline (err = %d)\n";

static void __exit mkiss_exit_driver(void)
{
      int ret;

      if ((ret = tty_unregister_ldisc(N_AX25)))
            printk(msg_unregfail, ret);
}

MODULE_AUTHOR("Ralf Baechle DL5RB <ralf@linux-mips.org>");
MODULE_DESCRIPTION("KISS driver for AX.25 over TTYs");
module_param(crc_force, int, 0);
MODULE_PARM_DESC(crc_force, "crc [0 = auto | 1 = none | 2 = flexnet | 3 = smack]");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_AX25);

module_init(mkiss_init_driver);
module_exit(mkiss_exit_driver);

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