/*
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * Copyright Jonathan Naylor G4KLX (g4klx@g4klx.demon.co.uk)
   * Copyright Darryl Miles G7LED (dlm@g7led.demon.co.uk)
   */
  #include <linux/errno.h>
  #include <linux/types.h>
  #include <linux/socket.h>
  #include <linux/in.h>
  #include <linux/kernel.h>
  #include <linux/timer.h>
  #include <linux/string.h>
  #include <linux/sockios.h>
  #include <linux/net.h>
  #include <linux/slab.h>
  #include <net/ax25.h>
  #include <linux/inet.h>
  #include <linux/netdevice.h>
  #include <linux/skbuff.h>
  #include <net/sock.h>
  #include <asm/uaccess.h>
  #include <linux/fcntl.h>
  #include <linux/mm.h>
  #include <linux/interrupt.h>
  #include <net/netrom.h>
  
  /*
   *	This is where all NET/ROM frames pass, except for IP-over-NET/ROM which
   *	cannot be fragmented in this manner.
   */
  void nr_output(struct sock *sk, struct sk_buff *skb)
  {
  	struct sk_buff *skbn;
  	unsigned char transport[NR_TRANSPORT_LEN];
  	int err, frontlen, len;
  
  	if (skb->len - NR_TRANSPORT_LEN > NR_MAX_PACKET_SIZE) {
  		/* Save a copy of the Transport Header */
  		skb_copy_from_linear_data(skb, transport, NR_TRANSPORT_LEN);
  		skb_pull(skb, NR_TRANSPORT_LEN);
  
  		frontlen = skb_headroom(skb);
  
  		while (skb->len > 0) {
  			if ((skbn = sock_alloc_send_skb(sk, frontlen + NR_MAX_PACKET_SIZE, 0, &err)) == NULL)
  				return;
  
  			skb_reserve(skbn, frontlen);
  
  			len = (NR_MAX_PACKET_SIZE > skb->len) ? skb->len : NR_MAX_PACKET_SIZE;
  
  			/* Copy the user data */
  			skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
  			skb_pull(skb, len);
  
  			/* Duplicate the Transport Header */
  			skb_push(skbn, NR_TRANSPORT_LEN);
  			skb_copy_to_linear_data(skbn, transport,
  						NR_TRANSPORT_LEN);
  			if (skb->len > 0)
  				skbn->data[4] |= NR_MORE_FLAG;
  
  			skb_queue_tail(&sk->sk_write_queue, skbn); /* Throw it on the queue */
  		}
  
  		kfree_skb(skb);
  	} else {
  		skb_queue_tail(&sk->sk_write_queue, skb);		/* Throw it on the queue */
  	}
  
  	nr_kick(sk);
  }
  
  /*
   *	This procedure is passed a buffer descriptor for an iframe. It builds
   *	the rest of the control part of the frame and then writes it out.
   */
  static void nr_send_iframe(struct sock *sk, struct sk_buff *skb)
  {
  	struct nr_sock *nr = nr_sk(sk);
  
  	if (skb == NULL)
  		return;
  
  	skb->data[2] = nr->vs;
  	skb->data[3] = nr->vr;
  
  	if (nr->condition & NR_COND_OWN_RX_BUSY)
  		skb->data[4] |= NR_CHOKE_FLAG;
  
  	nr_start_idletimer(sk);
  
  	nr_transmit_buffer(sk, skb);
  }
  
  void nr_send_nak_frame(struct sock *sk)
  {
  	struct sk_buff *skb, *skbn;
  	struct nr_sock *nr = nr_sk(sk);
  
  	if ((skb = skb_peek(&nr->ack_queue)) == NULL)
  		return;
  
  	if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL)
  		return;
  
  	skbn->data[2] = nr->va;
  	skbn->data[3] = nr->vr;
  
  	if (nr->condition & NR_COND_OWN_RX_BUSY)
  		skbn->data[4] |= NR_CHOKE_FLAG;
  
  	nr_transmit_buffer(sk, skbn);
  
  	nr->condition &= ~NR_COND_ACK_PENDING;
  	nr->vl         = nr->vr;
  
  	nr_stop_t1timer(sk);
  }
  
  void nr_kick(struct sock *sk)
  {
  	struct nr_sock *nr = nr_sk(sk);
  	struct sk_buff *skb, *skbn;
  	unsigned short start, end;
  
  	if (nr->state != NR_STATE_3)
  		return;
  
  	if (nr->condition & NR_COND_PEER_RX_BUSY)
  		return;
  
  	if (!skb_peek(&sk->sk_write_queue))
  		return;
  
  	start = (skb_peek(&nr->ack_queue) == NULL) ? nr->va : nr->vs;
  	end   = (nr->va + nr->window) % NR_MODULUS;
  
  	if (start == end)
  		return;
  
  	nr->vs = start;
  
  	/*
  	 * Transmit data until either we're out of data to send or
  	 * the window is full.
  	 */
  
  	/*
  	 * Dequeue the frame and copy it.
  	 */
  	skb = skb_dequeue(&sk->sk_write_queue);
  
  	do {
  		if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL) {
  			skb_queue_head(&sk->sk_write_queue, skb);
  			break;
  		}
  
  		skb_set_owner_w(skbn, sk);
  
  		/*
  		 * Transmit the frame copy.
  		 */
  		nr_send_iframe(sk, skbn);
  
  		nr->vs = (nr->vs + 1) % NR_MODULUS;
  
  		/*
  		 * Requeue the original data frame.
  		 */
  		skb_queue_tail(&nr->ack_queue, skb);
  
  	} while (nr->vs != end &&
  		 (skb = skb_dequeue(&sk->sk_write_queue)) != NULL);
  
  	nr->vl         = nr->vr;
  	nr->condition &= ~NR_COND_ACK_PENDING;
  
  	if (!nr_t1timer_running(sk))
  		nr_start_t1timer(sk);
  }
  
  void nr_transmit_buffer(struct sock *sk, struct sk_buff *skb)
  {
  	struct nr_sock *nr = nr_sk(sk);
  	unsigned char *dptr;
  
  	/*
  	 *	Add the protocol byte and network header.
  	 */
  	dptr = skb_push(skb, NR_NETWORK_LEN);
  
  	memcpy(dptr, &nr->source_addr, AX25_ADDR_LEN);
  	dptr[6] &= ~AX25_CBIT;
  	dptr[6] &= ~AX25_EBIT;
  	dptr[6] |= AX25_SSSID_SPARE;
  	dptr += AX25_ADDR_LEN;
  
  	memcpy(dptr, &nr->dest_addr, AX25_ADDR_LEN);
  	dptr[6] &= ~AX25_CBIT;
  	dptr[6] |= AX25_EBIT;
  	dptr[6] |= AX25_SSSID_SPARE;
  	dptr += AX25_ADDR_LEN;
  
  	*dptr++ = sysctl_netrom_network_ttl_initialiser;
  
  	if (!nr_route_frame(skb, NULL)) {
  		kfree_skb(skb);
  		nr_disconnect(sk, ENETUNREACH);
  	}
  }
  
  /*
   * The following routines are taken from page 170 of the 7th ARRL Computer
   * Networking Conference paper, as is the whole state machine.
   */
  
  void nr_establish_data_link(struct sock *sk)
  {
  	struct nr_sock *nr = nr_sk(sk);
  
  	nr->condition = 0x00;
  	nr->n2count   = 0;
  
  	nr_write_internal(sk, NR_CONNREQ);
  
  	nr_stop_t2timer(sk);
  	nr_stop_t4timer(sk);
  	nr_stop_idletimer(sk);
  	nr_start_t1timer(sk);
  }
  
  /*
   * Never send a NAK when we are CHOKEd.
   */
  void nr_enquiry_response(struct sock *sk)
  {
  	struct nr_sock *nr = nr_sk(sk);
  	int frametype = NR_INFOACK;
  
  	if (nr->condition & NR_COND_OWN_RX_BUSY) {
  		frametype |= NR_CHOKE_FLAG;
  	} else {
  		if (skb_peek(&nr->reseq_queue) != NULL)
  			frametype |= NR_NAK_FLAG;
  	}
  
  	nr_write_internal(sk, frametype);
  
  	nr->vl         = nr->vr;
  	nr->condition &= ~NR_COND_ACK_PENDING;
  }
  
  void nr_check_iframes_acked(struct sock *sk, unsigned short nr)
  {
  	struct nr_sock *nrom = nr_sk(sk);
  
  	if (nrom->vs == nr) {
  		nr_frames_acked(sk, nr);
  		nr_stop_t1timer(sk);
  		nrom->n2count = 0;
  	} else {
  		if (nrom->va != nr) {
  			nr_frames_acked(sk, nr);
  			nr_start_t1timer(sk);
  		}
  	}
  }