// SPDX-License-Identifier: GPL-2.0-only
/*
 *      Things to sort out:
 *
 *      o       tbusy handling
 *      o       allow users to set the parameters
 *      o       sync/async switching ?
 *
 *      Note: This does _not_ implement CCITT X.25 asynchronous framing
 *      recommendations. Its primarily for testing purposes. If you wanted
 *      to do CCITT then in theory all you need is to nick the HDLC async
 *      checksum routines from ppp.c
 *      Changes:
 *
 *      2000-10-29      Henner Eisen    lapb_data_indication() return status.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>

#include <linux/uaccess.h>
#include <linux/bitops.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/if_arp.h>
#include <linux/lapb.h>
#include <linux/init.h>
#include <linux/rtnetlink.h>
#include <linux/slab.h>
#include <net/x25device.h>
#include "x25_asy.h"

static struct net_device **x25_asy_devs;
static int x25_asy_maxdev = SL_NRUNIT;

module_param(x25_asy_maxdev, int, 0);
MODULE_LICENSE("GPL");

static int x25_asy_esc(unsigned char *p, unsigned char *d, int len);
static void x25_asy_unesc(struct x25_asy *sl, unsigned char c);
static void x25_asy_setup(struct net_device *dev);

/* Find a free X.25 channel, and link in this `tty' line. */
static struct x25_asy *x25_asy_alloc(void)
{
        struct net_device *dev = NULL;
        struct x25_asy *sl;
        int i;

        if (x25_asy_devs == NULL)
                return NULL;    /* Master array missing ! */

        for (i = 0; i < x25_asy_maxdev; i++) {
                dev = x25_asy_devs[i];

                /* Not allocated ? */
                if (dev == NULL)
                        break;

                sl = netdev_priv(dev);
                /* Not in use ? */
                if (!test_and_set_bit(SLF_INUSE, &sl->flags))
                        return sl;
        }


        /* Sorry, too many, all slots in use */
        if (i >= x25_asy_maxdev)
                return NULL;

        /* If no channels are available, allocate one */
        if (!dev) {
                char name[IFNAMSIZ];
                sprintf(name, "x25asy%d", i);

                dev = alloc_netdev(sizeof(struct x25_asy), name,
                                   NET_NAME_UNKNOWN, x25_asy_setup);
                if (!dev)
                        return NULL;

                /* Initialize channel control data */
                sl = netdev_priv(dev);
                dev->base_addr    = i;

                /* register device so that it can be ifconfig'ed       */
                if (register_netdev(dev) == 0) {
                        /* (Re-)Set the INUSE bit.   Very Important! */
                        set_bit(SLF_INUSE, &sl->flags);
                        x25_asy_devs[i] = dev;
                        return sl;
                } else {
                        pr_warn("%s(): register_netdev() failure\n", __func__);
                        free_netdev(dev);
                }
        }
        return NULL;
}


/* Free an X.25 channel. */
static void x25_asy_free(struct x25_asy *sl)
{
        /* Free all X.25 frame buffers. */
        kfree(sl->rbuff);
        sl->rbuff = NULL;
        kfree(sl->xbuff);
        sl->xbuff = NULL;

        if (!test_and_clear_bit(SLF_INUSE, &sl->flags))
                netdev_err(sl->dev, "x25_asy_free for already free unit\n");
}

static int x25_asy_change_mtu(struct net_device *dev, int newmtu)
{
        struct x25_asy *sl = netdev_priv(dev);
        unsigned char *xbuff, *rbuff;
        int len;

        len = 2 * newmtu;
        xbuff = kmalloc(len + 4, GFP_ATOMIC);
        rbuff = kmalloc(len + 4, GFP_ATOMIC);

        if (xbuff == NULL || rbuff == NULL) {
                kfree(xbuff);
                kfree(rbuff);
                return -ENOMEM;
        }

        spin_lock_bh(&sl->lock);
        xbuff    = xchg(&sl->xbuff, xbuff);
        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;

        rbuff    = xchg(&sl->rbuff, rbuff);
        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);
                }
        }

        dev->mtu    = newmtu;
        sl->buffsize = len;

        spin_unlock_bh(&sl->lock);

        kfree(xbuff);
        kfree(rbuff);
        return 0;
}


/* Set the "sending" flag.  This must be atomic, hence the ASM. */

static inline void x25_asy_lock(struct x25_asy *sl)
{
        netif_stop_queue(sl->dev);
}


/* Clear the "sending" flag.  This must be atomic, hence the ASM. */

static inline void x25_asy_unlock(struct x25_asy *sl)
{
        netif_wake_queue(sl->dev);
}

/* Send an LAPB frame to the LAPB module to process. */

static void x25_asy_bump(struct x25_asy *sl)
{
        struct net_device *dev = sl->dev;
        struct sk_buff *skb;
        int count;
        int err;

        count = sl->rcount;
        dev->stats.rx_bytes += count;

        skb = dev_alloc_skb(count);
        if (skb == NULL) {
                netdev_warn(sl->dev, "memory squeeze, dropping packet\n");
                dev->stats.rx_dropped++;
                return;
        }
        skb_put_data(skb, sl->rbuff, count);
        skb->protocol = x25_type_trans(skb, sl->dev);
        err = lapb_data_received(skb->dev, skb);
        if (err != LAPB_OK) {
                kfree_skb(skb);
                printk(KERN_DEBUG "x25_asy: data received err - %d\n", err);
        } else {
                dev->stats.rx_packets++;
        }
}

/* Encapsulate one IP datagram and stuff into a TTY queue. */
static void x25_asy_encaps(struct x25_asy *sl, unsigned char *icp, int len)
{
        unsigned char *p;
        int actual, count, mtu = sl->dev->mtu;

        if (len > mtu) {
                /* Sigh, shouldn't occur BUT ... */
                len = mtu;
                printk(KERN_DEBUG "%s: truncating oversized transmit packet!\n",
                                        sl->dev->name);
                sl->dev->stats.tx_dropped++;
                x25_asy_unlock(sl);
                return;
        }

        p = icp;
        count = x25_asy_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 driver.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);
        sl->xleft = count - actual;
        sl->xhead = sl->xbuff + actual;
        /* VSV */
        clear_bit(SLF_OUTWAIT, &sl->flags);     /* reset outfill flag */
}

/*
 * Called by the driver when there's room for more data.  If we have
 * more packets to send, we send them here.
 */
static void x25_asy_write_wakeup(struct tty_struct *tty)
{
        int actual;
        struct x25_asy *sl = tty->disc_data;

        /* First make sure we're connected. */
        if (!sl || sl->magic != X25_ASY_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);
                x25_asy_unlock(sl);
                return;
        }

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

static void x25_asy_timeout(struct net_device *dev, unsigned int txqueue)
{
        struct x25_asy *sl = netdev_priv(dev);

        spin_lock(&sl->lock);
        if (netif_queue_stopped(dev)) {
                /* May be we must check transmitter timeout here ?
                 *      14 Oct 1994 Dmitry Gorodchanin.
                 */
                netdev_warn(dev, "transmit timed out, %s?\n",
                            (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);
                x25_asy_unlock(sl);
        }
        spin_unlock(&sl->lock);
}

/* Encapsulate an IP datagram and kick it into a TTY queue. */

static netdev_tx_t x25_asy_xmit(struct sk_buff *skb,
                                      struct net_device *dev)
{
        struct x25_asy *sl = netdev_priv(dev);
        int err;

        if (!netif_running(sl->dev)) {
                netdev_err(dev, "xmit call when iface is down\n");
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }

        /* There should be a pseudo header of 1 byte added by upper layers.
         * Check to make sure it is there before reading it.
         */
        if (skb->len < 1) {
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }

        switch (skb->data[0]) {
        case X25_IFACE_DATA:
                break;
        case X25_IFACE_CONNECT: /* Connection request .. do nothing */
                err = lapb_connect_request(dev);
                if (err != LAPB_OK)
                        netdev_err(dev, "lapb_connect_request error: %d\n",
                                   err);
                kfree_skb(skb);
                return NETDEV_TX_OK;
        case X25_IFACE_DISCONNECT: /* do nothing - hang up ?? */
                err = lapb_disconnect_request(dev);
                if (err != LAPB_OK)
                        netdev_err(dev, "lapb_disconnect_request error: %d\n",
                                   err);
                fallthrough;
        default:
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }
        skb_pull(skb, 1);       /* Remove control byte */
        /*
         * If we are busy already- too bad.  We ought to be able
         * to queue things at this point, to allow for a little
         * frame buffer.  Oh well...
         * -----------------------------------------------------
         * I hate queues in X.25 driver. May be it's efficient,
         * but for me latency is more important. ;)
         * So, no queues !
         *        14 Oct 1994  Dmitry Gorodchanin.
         */

        err = lapb_data_request(dev, skb);
        if (err != LAPB_OK) {
                netdev_err(dev, "lapb_data_request error: %d\n", err);
                kfree_skb(skb);
                return NETDEV_TX_OK;
        }
        return NETDEV_TX_OK;
}


/*
 *      LAPB interface boilerplate
 */

/*
 *      Called when I frame data arrive. We add a pseudo header for upper
 *      layers and pass it to upper layers.
 */

static int x25_asy_data_indication(struct net_device *dev, struct sk_buff *skb)
{
        if (skb_cow(skb, 1)) {
                kfree_skb(skb);
                return NET_RX_DROP;
        }
        skb_push(skb, 1);
        skb->data[0] = X25_IFACE_DATA;

        skb->protocol = x25_type_trans(skb, dev);

        return netif_rx(skb);
}

/*
 *      Data has emerged from the LAPB protocol machine. We don't handle
 *      busy cases too well. Its tricky to see how to do this nicely -
 *      perhaps lapb should allow us to bounce this ?
 */

static void x25_asy_data_transmit(struct net_device *dev, struct sk_buff *skb)
{
        struct x25_asy *sl = netdev_priv(dev);

        spin_lock(&sl->lock);
        if (netif_queue_stopped(sl->dev) || sl->tty == NULL) {
                spin_unlock(&sl->lock);
                netdev_err(dev, "tbusy drop\n");
                kfree_skb(skb);
                return;
        }
        /* We were not busy, so we are now... :-) */
        if (skb != NULL) {
                x25_asy_lock(sl);
                dev->stats.tx_bytes += skb->len;
                x25_asy_encaps(sl, skb->data, skb->len);
                dev_kfree_skb(skb);
        }
        spin_unlock(&sl->lock);
}

/*
 *      LAPB connection establish/down information.
 */

static void x25_asy_connected(struct net_device *dev, int reason)
{
        struct x25_asy *sl = netdev_priv(dev);
        struct sk_buff *skb;
        unsigned char *ptr;

        skb = dev_alloc_skb(1);
        if (skb == NULL) {
                netdev_err(dev, "out of memory\n");
                return;
        }

        ptr  = skb_put(skb, 1);
        *ptr = X25_IFACE_CONNECT;

        skb->protocol = x25_type_trans(skb, sl->dev);
        netif_rx(skb);
}

static void x25_asy_disconnected(struct net_device *dev, int reason)
{
        struct x25_asy *sl = netdev_priv(dev);
        struct sk_buff *skb;
        unsigned char *ptr;

        skb = dev_alloc_skb(1);
        if (skb == NULL) {
                netdev_err(dev, "out of memory\n");
                return;
        }

        ptr  = skb_put(skb, 1);
        *ptr = X25_IFACE_DISCONNECT;

        skb->protocol = x25_type_trans(skb, sl->dev);
        netif_rx(skb);
}

static const struct lapb_register_struct x25_asy_callbacks = {
        .connect_confirmation = x25_asy_connected,
        .connect_indication = x25_asy_connected,
        .disconnect_confirmation = x25_asy_disconnected,
        .disconnect_indication = x25_asy_disconnected,
        .data_indication = x25_asy_data_indication,
        .data_transmit = x25_asy_data_transmit,
};


/* Open the low-level part of the X.25 channel. Easy! */
static int x25_asy_open(struct net_device *dev)
{
        struct x25_asy *sl = netdev_priv(dev);
        unsigned long len;

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

        /*
         * Allocate the X.25 frame buffers:
         *
         * rbuff        Receive buffer.
         * xbuff        Transmit buffer.
         */

        len = dev->mtu * 2;

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

        sl->buffsize = len;
        sl->rcount   = 0;
        sl->xleft    = 0;
        sl->flags   &= (1 << SLF_INUSE);      /* Clear ESCAPE & ERROR flags */

        return 0;

        /* Cleanup */
        kfree(sl->xbuff);
        sl->xbuff = NULL;
noxbuff:
        kfree(sl->rbuff);
        sl->rbuff = NULL;
norbuff:
        return -ENOMEM;
}


/* Close the low-level part of the X.25 channel. Easy! */
static int x25_asy_close(struct net_device *dev)
{
        struct x25_asy *sl = netdev_priv(dev);

        spin_lock(&sl->lock);
        if (sl->tty)
                clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);

        sl->rcount = 0;
        sl->xleft  = 0;
        spin_unlock(&sl->lock);
        return 0;
}

/*
 * Handle the 'receiver data ready' interrupt.
 * This function is called by the 'tty_io' module in the kernel when
 * a block of X.25 data has been received, which can now be decapsulated
 * and sent on to some IP layer for further processing.
 */

static void x25_asy_receive_buf(struct tty_struct *tty,
                                const unsigned char *cp, char *fp, int count)
{
        struct x25_asy *sl = tty->disc_data;

        if (!sl || sl->magic != X25_ASY_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;
                }
                x25_asy_unesc(sl, *cp++);
        }
}

/*
 * Open the high-level part of the X.25 channel.
 * This function is called by the TTY module when the
 * X.25 line discipline is called for.  Because we are
 * sure the tty line exists, we only have to link it to
 * a free X.25 channel...
 */

static int x25_asy_open_tty(struct tty_struct *tty)
{
        struct x25_asy *sl;
        int err;

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

        /* OK.  Find a free X.25 channel to use. */
        sl = x25_asy_alloc();
        if (sl == NULL)
                return -ENFILE;

        sl->tty = tty;
        tty->disc_data = sl;
        tty->receive_room = 65536;
        tty_driver_flush_buffer(tty);
        tty_ldisc_flush(tty);

        /* Restore default settings */
        sl->dev->type = ARPHRD_X25;

        /* Perform the low-level X.25 async init */
        err = x25_asy_open(sl->dev);
        if (err) {
                x25_asy_free(sl);
                return err;
        }
        /* Done.  We have linked the TTY line to a channel. */
        return 0;
}


/*
 * Close down an X.25 channel.
 * This means flushing out any pending queues, and then restoring the
 * TTY line discipline to what it was before it got hooked to X.25
 * (which usually is TTY again).
 */
static void x25_asy_close_tty(struct tty_struct *tty)
{
        struct x25_asy *sl = tty->disc_data;

        /* First make sure we're connected. */
        if (!sl || sl->magic != X25_ASY_MAGIC)
                return;

        rtnl_lock();
        if (sl->dev->flags & IFF_UP)
                dev_close(sl->dev);
        rtnl_unlock();

        tty->disc_data = NULL;
        sl->tty = NULL;
        x25_asy_free(sl);
}

 /************************************************************************
  *                     STANDARD X.25 ENCAPSULATION                      *
  ************************************************************************/

static int x25_asy_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++ = X25_END;       /* Send 10111110 bit seq */

        /*
         * For each byte in the packet, send the appropriate
         * character sequence, according to the X.25 protocol.
         */

        while (len-- > 0) {
                switch (c = *s++) {
                case X25_END:
                        *ptr++ = X25_ESC;
                        *ptr++ = X25_ESCAPE(X25_END);
                        break;
                case X25_ESC:
                        *ptr++ = X25_ESC;
                        *ptr++ = X25_ESCAPE(X25_ESC);
                        break;
                default:
                        *ptr++ = c;
                        break;
                }
        }
        *ptr++ = X25_END;
        return ptr - d;
}

static void x25_asy_unesc(struct x25_asy *sl, unsigned char s)
{

        switch (s) {
        case X25_END:
                if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
                    sl->rcount >= 2)
                        x25_asy_bump(sl);
                clear_bit(SLF_ESCAPE, &sl->flags);
                sl->rcount = 0;
                return;
        case X25_ESC:
                set_bit(SLF_ESCAPE, &sl->flags);
                return;
        case X25_ESCAPE(X25_ESC):
        case X25_ESCAPE(X25_END):
                if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
                        s = X25_UNESCAPE(s);
                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);
        }
}


/* Perform I/O control on an active X.25 channel. */
static int x25_asy_ioctl(struct tty_struct *tty, struct file *file,
                         unsigned int cmd,  unsigned long arg)
{
        struct x25_asy *sl = tty->disc_data;

        /* First make sure we're connected. */
        if (!sl || sl->magic != X25_ASY_MAGIC)
                return -EINVAL;

        switch (cmd) {
        case SIOCGIFNAME:
                if (copy_to_user((void __user *)arg, sl->dev->name,
                                        strlen(sl->dev->name) + 1))
                        return -EFAULT;
                return 0;
        case SIOCSIFHWADDR:
                return -EINVAL;
        default:
                return tty_mode_ioctl(tty, file, cmd, arg);
        }
}

static int x25_asy_open_dev(struct net_device *dev)
{
        int err;
        struct x25_asy *sl = netdev_priv(dev);
        if (sl->tty == NULL)
                return -ENODEV;

        err = lapb_register(dev, &x25_asy_callbacks);
        if (err != LAPB_OK)
                return -ENOMEM;

        netif_start_queue(dev);

        return 0;
}

static int x25_asy_close_dev(struct net_device *dev)
{
        int err;

        netif_stop_queue(dev);

        err = lapb_unregister(dev);
        if (err != LAPB_OK)
                pr_err("%s: lapb_unregister error: %d\n",
                       __func__, err);

        x25_asy_close(dev);

        return 0;
}

static const struct net_device_ops x25_asy_netdev_ops = {
        .ndo_open       = x25_asy_open_dev,
        .ndo_stop       = x25_asy_close_dev,
        .ndo_start_xmit = x25_asy_xmit,
        .ndo_tx_timeout = x25_asy_timeout,
        .ndo_change_mtu = x25_asy_change_mtu,
};

/* Initialise the X.25 driver.  Called by the device init code */
static void x25_asy_setup(struct net_device *dev)
{
        struct x25_asy *sl = netdev_priv(dev);

        sl->magic  = X25_ASY_MAGIC;
        sl->dev    = dev;
        spin_lock_init(&sl->lock);
        set_bit(SLF_INUSE, &sl->flags);

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

        dev->mtu                = SL_MTU;
        dev->min_mtu            = 0;
        dev->max_mtu            = 65534;
        dev->netdev_ops         = &x25_asy_netdev_ops;
        dev->watchdog_timeo     = HZ*20;
        dev->hard_header_len    = 0;
        dev->addr_len           = 0;
        dev->type               = ARPHRD_X25;
        dev->tx_queue_len       = 10;

        /* When transmitting data:
         * first this driver removes a pseudo header of 1 byte,
         * then the lapb module prepends an LAPB header of at most 3 bytes.
         */
        dev->needed_headroom    = 3 - 1;

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

static struct tty_ldisc_ops x25_ldisc = {
        .owner          = THIS_MODULE,
        .magic          = TTY_LDISC_MAGIC,
        .name           = "X.25",
        .open           = x25_asy_open_tty,
        .close          = x25_asy_close_tty,
        .ioctl          = x25_asy_ioctl,
        .receive_buf    = x25_asy_receive_buf,
        .write_wakeup   = x25_asy_write_wakeup,
};

static int __init init_x25_asy(void)
{
        if (x25_asy_maxdev < 4)
                x25_asy_maxdev = 4; /* Sanity */

        pr_info("X.25 async: version 0.00 ALPHA (dynamic channels, max=%d)\n",
                x25_asy_maxdev);

        x25_asy_devs = kcalloc(x25_asy_maxdev, sizeof(struct net_device *),
                                GFP_KERNEL);
        if (!x25_asy_devs)
                return -ENOMEM;

        return tty_register_ldisc(N_X25, &x25_ldisc);
}


static void __exit exit_x25_asy(void)
{
        struct net_device *dev;
        int i;

        for (i = 0; i < x25_asy_maxdev; i++) {
                dev = x25_asy_devs[i];
                if (dev) {
                        struct x25_asy *sl = netdev_priv(dev);

                        spin_lock_bh(&sl->lock);
                        if (sl->tty)
                                tty_hangup(sl->tty);

                        spin_unlock_bh(&sl->lock);
                        /*
                         * VSV = if dev->start==0, then device
                         * unregistered while close proc.
                         */
                        unregister_netdev(dev);
                        free_netdev(dev);
                }
        }

        kfree(x25_asy_devs);
        tty_unregister_ldisc(N_X25);
}

module_init(init_x25_asy);
module_exit(exit_x25_asy);