// SPDX-License-Identifier: GPL-2.0-only
/*
 * File: pep-gprs.c
 *
 * GPRS over Phonet pipe end point socket
 *
 * Copyright (C) 2008 Nokia Corporation.
 *
 * Author: Rémi Denis-Courmont
 */

#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <net/sock.h>

#include <linux/if_phonet.h>
#include <net/tcp_states.h>
#include <net/phonet/gprs.h>

#define GPRS_DEFAULT_MTU 1400

struct gprs_dev {
        struct sock             *sk;
        void                    (*old_state_change)(struct sock *);
        void                    (*old_data_ready)(struct sock *);
        void                    (*old_write_space)(struct sock *);

        struct net_device       *dev;
};

static __be16 gprs_type_trans(struct sk_buff *skb)
{
        const u8 *pvfc;
        u8 buf;

        pvfc = skb_header_pointer(skb, 0, 1, &buf);
        if (!pvfc)
                return htons(0);
        /* Look at IP version field */
        switch (*pvfc >> 4) {
        case 4:
                return htons(ETH_P_IP);
        case 6:
                return htons(ETH_P_IPV6);
        }
        return htons(0);
}

static void gprs_writeable(struct gprs_dev *gp)
{
        struct net_device *dev = gp->dev;

        if (pep_writeable(gp->sk))
                netif_wake_queue(dev);
}

/*
 * Socket callbacks
 */

static void gprs_state_change(struct sock *sk)
{
        struct gprs_dev *gp = sk->sk_user_data;

        if (sk->sk_state == TCP_CLOSE_WAIT) {
                struct net_device *dev = gp->dev;

                netif_stop_queue(dev);
                netif_carrier_off(dev);
        }
}

static int gprs_recv(struct gprs_dev *gp, struct sk_buff *skb)
{
        struct net_device *dev = gp->dev;
        int err = 0;
        __be16 protocol = gprs_type_trans(skb);

        if (!protocol) {
                err = -EINVAL;
                goto drop;
        }

        if (skb_headroom(skb) & 3) {
                struct sk_buff *rskb, *fs;
                int flen = 0;

                /* Phonet Pipe data header may be misaligned (3 bytes),
                 * so wrap the IP packet as a single fragment of an head-less
                 * socket buffer. The network stack will pull what it needs,
                 * but at least, the whole IP payload is not memcpy'd. */
                rskb = netdev_alloc_skb(dev, 0);
                if (!rskb) {
                        err = -ENOBUFS;
                        goto drop;
                }
                skb_shinfo(rskb)->frag_list = skb;
                rskb->len += skb->len;
                rskb->data_len += rskb->len;
                rskb->truesize += rskb->len;

                /* Avoid nested fragments */
                skb_walk_frags(skb, fs)
                        flen += fs->len;
                skb->next = skb_shinfo(skb)->frag_list;
                skb_frag_list_init(skb);
                skb->len -= flen;
                skb->data_len -= flen;
                skb->truesize -= flen;

                skb = rskb;
        }

        skb->protocol = protocol;
        skb_reset_mac_header(skb);
        skb->dev = dev;

        if (likely(dev->flags & IFF_UP)) {
                dev->stats.rx_packets++;
                dev->stats.rx_bytes += skb->len;
                netif_rx(skb);
                skb = NULL;
        } else
                err = -ENODEV;

drop:
        if (skb) {
                dev_kfree_skb(skb);
                dev->stats.rx_dropped++;
        }
        return err;
}

static void gprs_data_ready(struct sock *sk)
{
        struct gprs_dev *gp = sk->sk_user_data;
        struct sk_buff *skb;

        while ((skb = pep_read(sk)) != NULL) {
                skb_orphan(skb);
                gprs_recv(gp, skb);
        }
}

static void gprs_write_space(struct sock *sk)
{
        struct gprs_dev *gp = sk->sk_user_data;

        if (netif_running(gp->dev))
                gprs_writeable(gp);
}

/*
 * Network device callbacks
 */

static int gprs_open(struct net_device *dev)
{
        struct gprs_dev *gp = netdev_priv(dev);

        gprs_writeable(gp);
        return 0;
}

static int gprs_close(struct net_device *dev)
{
        netif_stop_queue(dev);
        return 0;
}

static netdev_tx_t gprs_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct gprs_dev *gp = netdev_priv(dev);
        struct sock *sk = gp->sk;
        int len, err;

        switch (skb->protocol) {
        case  htons(ETH_P_IP):
        case  htons(ETH_P_IPV6):
                break;
        default:
                dev_kfree_skb(skb);
                return NETDEV_TX_OK;
        }

        skb_orphan(skb);
        skb_set_owner_w(skb, sk);
        len = skb->len;
        err = pep_write(sk, skb);
        if (err) {
                net_dbg_ratelimited("%s: TX error (%d)\n", dev->name, err);
                dev->stats.tx_aborted_errors++;
                dev->stats.tx_errors++;
        } else {
                dev->stats.tx_packets++;
                dev->stats.tx_bytes += len;
        }

        netif_stop_queue(dev);
        if (pep_writeable(sk))
                netif_wake_queue(dev);
        return NETDEV_TX_OK;
}

static const struct net_device_ops gprs_netdev_ops = {
        .ndo_open       = gprs_open,
        .ndo_stop       = gprs_close,
        .ndo_start_xmit = gprs_xmit,
};

static void gprs_setup(struct net_device *dev)
{
        dev->features           = NETIF_F_FRAGLIST;
        dev->type               = ARPHRD_PHONET_PIPE;
        dev->flags              = IFF_POINTOPOINT | IFF_NOARP;
        dev->mtu                = GPRS_DEFAULT_MTU;
        dev->min_mtu            = 576;
        dev->max_mtu            = (PHONET_MAX_MTU - 11);
        dev->hard_header_len    = 0;
        dev->addr_len           = 0;
        dev->tx_queue_len       = 10;

        dev->netdev_ops         = &gprs_netdev_ops;
        dev->needs_free_netdev  = true;
}

/*
 * External interface
 */

/*
 * Attach a GPRS interface to a datagram socket.
 * Returns the interface index on success, negative error code on error.
 */
int gprs_attach(struct sock *sk)
{
        static const char ifname[] = "gprs%d";
        struct gprs_dev *gp;
        struct net_device *dev;
        int err;

        if (unlikely(sk->sk_type == SOCK_STREAM))
                return -EINVAL; /* need packet boundaries */

        /* Create net device */
        dev = alloc_netdev(sizeof(*gp), ifname, NET_NAME_UNKNOWN, gprs_setup);
        if (!dev)
                return -ENOMEM;
        gp = netdev_priv(dev);
        gp->sk = sk;
        gp->dev = dev;

        netif_stop_queue(dev);
        err = register_netdev(dev);
        if (err) {
                free_netdev(dev);
                return err;
        }

        lock_sock(sk);
        if (unlikely(sk->sk_user_data)) {
                err = -EBUSY;
                goto out_rel;
        }
        if (unlikely((1 << sk->sk_state & (TCPF_CLOSE|TCPF_LISTEN)) ||
                        sock_flag(sk, SOCK_DEAD))) {
                err = -EINVAL;
                goto out_rel;
        }
        sk->sk_user_data        = gp;
        gp->old_state_change    = sk->sk_state_change;
        gp->old_data_ready      = sk->sk_data_ready;
        gp->old_write_space     = sk->sk_write_space;
        sk->sk_state_change     = gprs_state_change;
        sk->sk_data_ready       = gprs_data_ready;
        sk->sk_write_space      = gprs_write_space;
        release_sock(sk);
        sock_hold(sk);

        printk(KERN_DEBUG"%s: attached\n", dev->name);
        return dev->ifindex;

out_rel:
        release_sock(sk);
        unregister_netdev(dev);
        return err;
}

void gprs_detach(struct sock *sk)
{
        struct gprs_dev *gp = sk->sk_user_data;
        struct net_device *dev = gp->dev;

        lock_sock(sk);
        sk->sk_user_data        = NULL;
        sk->sk_state_change     = gp->old_state_change;
        sk->sk_data_ready       = gp->old_data_ready;
        sk->sk_write_space      = gp->old_write_space;
        release_sock(sk);

        printk(KERN_DEBUG"%s: detached\n", dev->name);
        unregister_netdev(dev);
        sock_put(sk);
}