// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      "LAPB via ethernet" driver release 001
 *
 *      This code REQUIRES 2.1.15 or higher/ NET3.038
 *
 *      This is a "pseudo" network driver to allow LAPB over Ethernet.
 *
 *      This driver can use any ethernet destination address, and can be
 *      limited to accept frames from one dedicated ethernet card only.
 *
 *      History
 *      LAPBETH 001     Jonathan Naylor         Cloned from bpqether.c
 *      2000-10-29      Henner Eisen    lapb_data_indication() return status.
 *      2000-11-14      Henner Eisen    dev_hold/put, NETDEV_GOING_DOWN support
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/net.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/stat.h>
#include <linux/module.h>
#include <linux/lapb.h>
#include <linux/init.h>

#include <net/netdev_lock.h>
#include <net/x25device.h>

static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };

/* If this number is made larger, check that the temporary string buffer
 * in lapbeth_new_device is large enough to store the probe device name.
 */
#define MAXLAPBDEV 100

struct lapbethdev {
        struct list_head        node;
        struct net_device       *ethdev;        /* link to ethernet device */
        struct net_device       *axdev;         /* lapbeth device (lapb#) */
        bool                    up;
        spinlock_t              up_lock;        /* Protects "up" */
        struct sk_buff_head     rx_queue;
        struct napi_struct      napi;
};

static LIST_HEAD(lapbeth_devices);

static void lapbeth_connected(struct net_device *dev, int reason);
static void lapbeth_disconnected(struct net_device *dev, int reason);

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

/*      Get the LAPB device for the ethernet device
 */
static struct lapbethdev *lapbeth_get_x25_dev(struct net_device *dev)
{
        struct lapbethdev *lapbeth;

        list_for_each_entry_rcu(lapbeth, &lapbeth_devices, node, lockdep_rtnl_is_held()) {
                if (lapbeth->ethdev == dev)
                        return lapbeth;
        }
        return NULL;
}

static __inline__ int dev_is_ethdev(struct net_device *dev)
{
        return dev->type == ARPHRD_ETHER && !netdev_need_ops_lock(dev);
}

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

static int lapbeth_napi_poll(struct napi_struct *napi, int budget)
{
        struct lapbethdev *lapbeth = container_of(napi, struct lapbethdev,
                                                  napi);
        struct sk_buff *skb;
        int processed = 0;

        for (; processed < budget; ++processed) {
                skb = skb_dequeue(&lapbeth->rx_queue);
                if (!skb)
                        break;
                netif_receive_skb_core(skb);
        }

        if (processed < budget)
                napi_complete(napi);

        return processed;
}

/*      Receive a LAPB frame via an ethernet interface.
 */
static int lapbeth_rcv(struct sk_buff *skb, struct net_device *dev,
                       struct packet_type *ptype, struct net_device *orig_dev)
{
        int len, err;
        struct lapbethdev *lapbeth;

        if (dev_net(dev) != &init_net)
                goto drop;

        skb = skb_share_check(skb, GFP_ATOMIC);
        if (!skb)
                return NET_RX_DROP;

        if (!pskb_may_pull(skb, 2))
                goto drop;

        rcu_read_lock();
        lapbeth = lapbeth_get_x25_dev(dev);
        if (!lapbeth)
                goto drop_unlock_rcu;
        spin_lock_bh(&lapbeth->up_lock);
        if (!lapbeth->up)
                goto drop_unlock;

        len = skb->data[0] + skb->data[1] * 256;
        dev->stats.rx_packets++;
        dev->stats.rx_bytes += len;

        skb_pull(skb, 2);       /* Remove the length bytes */
        skb_trim(skb, len);     /* Set the length of the data */

        err = lapb_data_received(lapbeth->axdev, skb);
        if (err != LAPB_OK) {
                printk(KERN_DEBUG "lapbether: lapb_data_received err - %d\n", err);
                goto drop_unlock;
        }
out:
        spin_unlock_bh(&lapbeth->up_lock);
        rcu_read_unlock();
        return 0;
drop_unlock:
        kfree_skb(skb);
        goto out;
drop_unlock_rcu:
        rcu_read_unlock();
drop:
        kfree_skb(skb);
        return 0;
}

static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        unsigned char *ptr;

        if (skb_cow(skb, 1)) {
                kfree_skb(skb);
                return NET_RX_DROP;
        }

        skb_push(skb, 1);

        ptr  = skb->data;
        *ptr = X25_IFACE_DATA;

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

        skb_queue_tail(&lapbeth->rx_queue, skb);
        napi_schedule(&lapbeth->napi);
        return NET_RX_SUCCESS;
}

/*      Send a LAPB frame via an ethernet interface
 */
static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
                                struct net_device *dev)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        int err;

        spin_lock_bh(&lapbeth->up_lock);
        if (!lapbeth->up)
                goto drop;

        /* 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)
                goto drop;

        switch (skb->data[0]) {
        case X25_IFACE_DATA:
                break;
        case X25_IFACE_CONNECT:
                err = lapb_connect_request(dev);
                if (err == LAPB_CONNECTED)
                        lapbeth_connected(dev, LAPB_OK);
                else if (err != LAPB_OK)
                        pr_err("lapb_connect_request error: %d\n", err);
                goto drop;
        case X25_IFACE_DISCONNECT:
                err = lapb_disconnect_request(dev);
                if (err == LAPB_NOTCONNECTED)
                        lapbeth_disconnected(dev, LAPB_OK);
                else if (err != LAPB_OK)
                        pr_err("lapb_disconnect_request err: %d\n", err);
                fallthrough;
        default:
                goto drop;
        }

        skb_pull(skb, 1);

        err = lapb_data_request(dev, skb);
        if (err != LAPB_OK) {
                pr_err("lapb_data_request error - %d\n", err);
                goto drop;
        }
out:
        spin_unlock_bh(&lapbeth->up_lock);
        return NETDEV_TX_OK;
drop:
        kfree_skb(skb);
        goto out;
}

static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)
{
        struct lapbethdev *lapbeth = netdev_priv(ndev);
        unsigned char *ptr;
        struct net_device *dev;
        int size = skb->len;

        ptr = skb_push(skb, 2);

        *ptr++ = size % 256;
        *ptr++ = size / 256;

        ndev->stats.tx_packets++;
        ndev->stats.tx_bytes += size;

        skb->dev = dev = lapbeth->ethdev;

        skb->protocol = htons(ETH_P_DEC);

        skb_reset_network_header(skb);

        dev_hard_header(skb, dev, ETH_P_DEC, bcast_addr, NULL, 0);

        dev_queue_xmit(skb);
}

static void lapbeth_connected(struct net_device *dev, int reason)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        unsigned char *ptr;
        struct sk_buff *skb = __dev_alloc_skb(1, GFP_ATOMIC | __GFP_NOMEMALLOC);

        if (!skb)
                return;

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

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

        skb_queue_tail(&lapbeth->rx_queue, skb);
        napi_schedule(&lapbeth->napi);
}

static void lapbeth_disconnected(struct net_device *dev, int reason)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        unsigned char *ptr;
        struct sk_buff *skb = __dev_alloc_skb(1, GFP_ATOMIC | __GFP_NOMEMALLOC);

        if (!skb)
                return;

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

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

        skb_queue_tail(&lapbeth->rx_queue, skb);
        napi_schedule(&lapbeth->napi);
}

/*      Set AX.25 callsign
 */
static int lapbeth_set_mac_address(struct net_device *dev, void *addr)
{
        struct sockaddr *sa = addr;

        dev_addr_set(dev, sa->sa_data);
        return 0;
}

static const struct lapb_register_struct lapbeth_callbacks = {
        .connect_confirmation    = lapbeth_connected,
        .connect_indication      = lapbeth_connected,
        .disconnect_confirmation = lapbeth_disconnected,
        .disconnect_indication   = lapbeth_disconnected,
        .data_indication         = lapbeth_data_indication,
        .data_transmit           = lapbeth_data_transmit,
};

/* open/close a device
 */
static int lapbeth_open(struct net_device *dev)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        int err;

        napi_enable(&lapbeth->napi);

        err = lapb_register(dev, &lapbeth_callbacks);
        if (err != LAPB_OK) {
                napi_disable(&lapbeth->napi);
                pr_err("lapb_register error: %d\n", err);
                return -ENODEV;
        }

        spin_lock_bh(&lapbeth->up_lock);
        lapbeth->up = true;
        spin_unlock_bh(&lapbeth->up_lock);

        return 0;
}

static int lapbeth_close(struct net_device *dev)
{
        struct lapbethdev *lapbeth = netdev_priv(dev);
        int err;

        spin_lock_bh(&lapbeth->up_lock);
        lapbeth->up = false;
        spin_unlock_bh(&lapbeth->up_lock);

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

        napi_disable(&lapbeth->napi);

        return 0;
}

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

static const struct net_device_ops lapbeth_netdev_ops = {
        .ndo_open            = lapbeth_open,
        .ndo_stop            = lapbeth_close,
        .ndo_start_xmit      = lapbeth_xmit,
        .ndo_set_mac_address = lapbeth_set_mac_address,
};

static void lapbeth_setup(struct net_device *dev)
{
        netdev_lockdep_set_classes(dev);
        dev->netdev_ops      = &lapbeth_netdev_ops;
        dev->needs_free_netdev = true;
        dev->type            = ARPHRD_X25;
        dev->hard_header_len = 0;
        dev->mtu             = 1000;
        dev->addr_len        = 0;
}

/*      Setup a new device.
 */
static int lapbeth_new_device(struct net_device *dev)
{
        struct net_device *ndev;
        struct lapbethdev *lapbeth;
        int rc = -ENOMEM;

        ASSERT_RTNL();

        if (dev->type != ARPHRD_ETHER)
                return -EINVAL;

        ndev = alloc_netdev(sizeof(*lapbeth), "lapb%d", NET_NAME_UNKNOWN,
                            lapbeth_setup);
        if (!ndev)
                goto out;

        /* 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,
         * then this driver prepends a length field of 2 bytes,
         * then the underlying Ethernet device prepends its own header.
         */
        ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len
                                           + dev->needed_headroom;
        ndev->needed_tailroom = dev->needed_tailroom;

        lapbeth = netdev_priv(ndev);
        lapbeth->axdev = ndev;

        dev_hold(dev);
        lapbeth->ethdev = dev;

        lapbeth->up = false;
        spin_lock_init(&lapbeth->up_lock);

        skb_queue_head_init(&lapbeth->rx_queue);
        netif_napi_add_weight(ndev, &lapbeth->napi, lapbeth_napi_poll, 16);

        rc = -EIO;
        if (register_netdevice(ndev))
                goto fail;

        list_add_rcu(&lapbeth->node, &lapbeth_devices);
        rc = 0;
out:
        return rc;
fail:
        dev_put(dev);
        free_netdev(ndev);
        goto out;
}

/*      Free a lapb network device.
 */
static void lapbeth_free_device(struct lapbethdev *lapbeth)
{
        dev_put(lapbeth->ethdev);
        list_del_rcu(&lapbeth->node);
        unregister_netdevice(lapbeth->axdev);
}

/*      Handle device status changes.
 *
 * Called from notifier with RTNL held.
 */
static int lapbeth_device_event(struct notifier_block *this,
                                unsigned long event, void *ptr)
{
        struct lapbethdev *lapbeth;
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);

        if (dev_net(dev) != &init_net)
                return NOTIFY_DONE;

        if (!dev_is_ethdev(dev) && !lapbeth_get_x25_dev(dev))
                return NOTIFY_DONE;

        switch (event) {
        case NETDEV_UP:
                /* New ethernet device -> new LAPB interface     */
                if (!lapbeth_get_x25_dev(dev))
                        lapbeth_new_device(dev);
                break;
        case NETDEV_GOING_DOWN:
                /* ethernet device closes -> close LAPB interface */
                lapbeth = lapbeth_get_x25_dev(dev);
                if (lapbeth)
                        dev_close(lapbeth->axdev);
                break;
        case NETDEV_UNREGISTER:
                /* ethernet device disappears -> remove LAPB interface */
                lapbeth = lapbeth_get_x25_dev(dev);
                if (lapbeth)
                        lapbeth_free_device(lapbeth);
                break;
        }

        return NOTIFY_DONE;
}

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

static struct packet_type lapbeth_packet_type __read_mostly = {
        .type = cpu_to_be16(ETH_P_DEC),
        .func = lapbeth_rcv,
};

static struct notifier_block lapbeth_dev_notifier = {
        .notifier_call = lapbeth_device_event,
};

static const char banner[] __initconst =
        KERN_INFO "LAPB Ethernet driver version 0.02\n";

static int __init lapbeth_init_driver(void)
{
        dev_add_pack(&lapbeth_packet_type);

        register_netdevice_notifier(&lapbeth_dev_notifier);

        printk(banner);

        return 0;
}
module_init(lapbeth_init_driver);

static void __exit lapbeth_cleanup_driver(void)
{
        struct lapbethdev *lapbeth;
        struct list_head *entry, *tmp;

        dev_remove_pack(&lapbeth_packet_type);
        unregister_netdevice_notifier(&lapbeth_dev_notifier);

        rtnl_lock();
        list_for_each_safe(entry, tmp, &lapbeth_devices) {
                lapbeth = list_entry(entry, struct lapbethdev, node);

                dev_put(lapbeth->ethdev);
                unregister_netdevice(lapbeth->axdev);
        }
        rtnl_unlock();
}
module_exit(lapbeth_cleanup_driver);

MODULE_AUTHOR("Jonathan Naylor <g4klx@g4klx.demon.co.uk>");
MODULE_DESCRIPTION("The unofficial LAPB over Ethernet driver");
MODULE_LICENSE("GPL");