mkiss.c

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/*
 *  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 <[email protected]>
 * Copyright (C) 2004, 05 Ralf Baechle DL5RB <[email protected]>
 * Copyright (C) 2004, 05 Thomas Osterried DL9SAU <[email protected]>
 */
#include <linux/module.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/slab.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 <linux/compat.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     */

    /* 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->dev->stats.rx_errors++;
                spin_unlock_bh(&ax->buflock);

                return;
            }
            if (ax->crcmode != CRC_MODE_SMACK && ax->crcauto) {
                printk(KERN_INFO
                       "mkiss: %s: Switching 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->dev->stats.rx_errors++;
                spin_unlock_bh(&ax->buflock);
                return;
            }
            if (ax->crcmode != CRC_MODE_FLEX && ax->crcauto) {
                printk(KERN_INFO
                       "mkiss: %s: Switching 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;
        }
    }

    count = ax->rcount;

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

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

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->dev->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);
    netif_addr_lock(dev);
    memcpy(dev->dev_addr, &sa->sax25_call, AX25_ADDR_LEN);
    netif_addr_unlock(dev);
    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;
            dev->stats.tx_dropped++;
        }
    }

    ax->xhead = ax->xbuff;

    if (ax->rcount) {
        if (ax->rcount <= len) {
            memcpy(ax->rbuff, orbuff, ax->rcount);
        } else  {
            ax->rcount = 0;
            dev->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);
        dev->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, 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, 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, ax->xbuff, crc, len+2);
            break;

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

    set_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags);
    actual = ax->tty->ops->write(ax->tty, ax->xbuff, count);
    dev->stats.tx_packets++;
    dev->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 netdev_tx_t 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 NETDEV_TX_BUSY;
    }

    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 NETDEV_TX_BUSY;
        }

        printk(KERN_ERR "mkiss: %s: transmit timed out, %s?\n", dev->name,
               (tty_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 NETDEV_TX_OK;
}

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

static const struct net_device_ops ax_netdev_ops = {
    .ndo_open            = ax_open_dev,
    .ndo_stop            = ax_close,
    .ndo_start_xmit      = ax_xmit,
    .ndo_set_mac_address = ax_set_mac_address,
};

static void ax_setup(struct net_device *dev)
{
    /* Finish setting up the DEVICE info. */
    dev->mtu             = AX_MTU;
    dev->hard_header_len = 0;
    dev->addr_len        = 0;
    dev->type            = ARPHRD_AX25;
    dev->tx_queue_len    = 10;
    dev->header_ops      = &ax_header_ops;
    dev->netdev_ops      = &ax_netdev_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;
    if (tty->ops->write == NULL)
        return -EOPNOTSUPP;

    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);
    sema_init(&ax->dead_sem, 0);

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

    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_bh(&disc_data_lock);
    ax = tty->disc_data;
    tty->disc_data = NULL;
    write_unlock_bh(&disc_data_lock);

    if (!ax)
        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;
    unsigned int tmp, err;

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

    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;
}

#ifdef CONFIG_COMPAT
static long mkiss_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:
        return mkiss_ioctl(tty, file, cmd,
                   (unsigned long)compat_ptr(arg));
    }

    return -ENOIOCTLCMD;
}
#endif

/*
 * 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->dev->stats.rx_errors++;
            cp++;
            continue;
        }

        kiss_unesc(ax, *cp++);
    }

    mkiss_put(ax);
    tty_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->ops->write(tty, ax->xhead, ax->xleft);
    ax->xleft -= actual;
    ax->xhead += actual;

out:
    mkiss_put(ax);
}

static struct tty_ldisc_ops ax_ldisc = {
    .owner      = THIS_MODULE,
    .magic      = TTY_LDISC_MAGIC,
    .name       = "mkiss",
    .open       = mkiss_open,
    .close      = mkiss_close,
    .ioctl      = mkiss_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = mkiss_compat_ioctl,
#endif
    .receive_buf    = mkiss_receive_buf,
    .write_wakeup   = mkiss_write_wakeup
};

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

static int __init mkiss_init_driver(void)
{
    int status;

    printk(banner);

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

    return status;
}

static const char msg_unregfail[] = 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 <[email protected]>");
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);