/*
   * File: pep-gprs.c
   *
   * GPRS over Phonet pipe end point socket
   *
   * Copyright (C) 2008 Nokia Corporation.
   *

   * Author: Rémi Denis-Courmont

   *
   * This program is free software; you can redistribute 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 that 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., 51 Franklin St, Fifth Floor, Boston, MA
   * 02110-1301 USA
   */
  
  #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 *, int);
  	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, int len)
  {

  	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) {
  		LIMIT_NETDEBUG(KERN_WARNING"%s: TX error (%d)
  ",
  				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 int gprs_set_mtu(struct net_device *dev, int new_mtu)

  {
  	if ((new_mtu < 576) || (new_mtu > (PHONET_MAX_MTU - 11)))
  		return -EINVAL;

  	dev->mtu = new_mtu;

  	return 0;
  }

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

  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->hard_header_len	= 0;
  	dev->addr_len		= 0;
  	dev->tx_queue_len	= 10;

  	dev->netdev_ops		= &gprs_netdev_ops;

  	dev->destructor		= free_netdev;

  }
  
  /*
   * 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, 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
  ", 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
  ", dev->name);
  	unregister_netdev(dev);

  	sock_put(sk);

  }