/*
   *	X.25 Packet Layer release 002
   *
   *	This is ALPHA test software. This code may break your machine,
   *	randomly fail to work with new releases, misbehave and/or generally
   *	screw up. It might even work.
   *
   *	This code REQUIRES 2.1.15 or higher
   *
   *	This module:
   *		This module 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.
   *
   *	History
   *	X.25 001	Jonathan Naylor	Started coding.
   *	X.25 002	Jonathan Naylor	New timer architecture.
   *	2000-09-04	Henner Eisen	Prevented x25_output() skb leakage.
   *	2000-10-27	Henner Eisen	MSG_DONTWAIT for fragment allocation.
   *	2000-11-10	Henner Eisen	x25_send_iframe(): re-queued frames
   *					needed cleaned seq-number fields.
   */
  
  #include <linux/slab.h>
  #include <linux/socket.h>
  #include <linux/kernel.h>
  #include <linux/string.h>
  #include <linux/skbuff.h>
  #include <net/sock.h>
  #include <net/x25.h>
  
  static int x25_pacsize_to_bytes(unsigned int pacsize)
  {
  	int bytes = 1;
  
  	if (!pacsize)
  		return 128;
  
  	while (pacsize-- > 0)
  		bytes *= 2;
  
  	return bytes;
  }
  
  /*
   *	This is where all X.25 information frames pass.
   *
   *      Returns the amount of user data bytes sent on success
   *      or a negative error code on failure.
   */
  int x25_output(struct sock *sk, struct sk_buff *skb)
  {
  	struct sk_buff *skbn;
  	unsigned char header[X25_EXT_MIN_LEN];
  	int err, frontlen, len;
  	int sent=0, noblock = X25_SKB_CB(skb)->flags & MSG_DONTWAIT;
  	struct x25_sock *x25 = x25_sk(sk);
  	int header_len = x25->neighbour->extended ? X25_EXT_MIN_LEN :
  						    X25_STD_MIN_LEN;
  	int max_len = x25_pacsize_to_bytes(x25->facilities.pacsize_out);
  
  	if (skb->len - header_len > max_len) {
  		/* Save a copy of the Header */
  		skb_copy_from_linear_data(skb, header, header_len);
  		skb_pull(skb, header_len);
  
  		frontlen = skb_headroom(skb);
  
  		while (skb->len > 0) {
  			release_sock(sk);
  			skbn = sock_alloc_send_skb(sk, frontlen + max_len,
  						   noblock, &err);
  			lock_sock(sk);
  			if (!skbn) {
  				if (err == -EWOULDBLOCK && noblock){
  					kfree_skb(skb);
  					return sent;
  				}
  				SOCK_DEBUG(sk, "x25_output: fragment alloc"
  					       " failed, err=%d, %d bytes "
  					       "sent
  ", err, sent);
  				return err;
  			}
  
  			skb_reserve(skbn, frontlen);
  
  			len = max_len > skb->len ? skb->len : max_len;
  
  			/* Copy the user data */
  			skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
  			skb_pull(skb, len);
  
  			/* Duplicate the Header */
  			skb_push(skbn, header_len);
  			skb_copy_to_linear_data(skbn, header, header_len);
  
  			if (skb->len > 0) {
  				if (x25->neighbour->extended)
  					skbn->data[3] |= X25_EXT_M_BIT;
  				else
  					skbn->data[2] |= X25_STD_M_BIT;
  			}
  
  			skb_queue_tail(&sk->sk_write_queue, skbn);
  			sent += len;
  		}
  
  		kfree_skb(skb);
  	} else {
  		skb_queue_tail(&sk->sk_write_queue, skb);
  		sent = skb->len - header_len;
  	}
  	return sent;
  }
  
  /*
   *	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 x25_send_iframe(struct sock *sk, struct sk_buff *skb)
  {
  	struct x25_sock *x25 = x25_sk(sk);
  
  	if (!skb)
  		return;
  
  	if (x25->neighbour->extended) {
  		skb->data[2]  = (x25->vs << 1) & 0xFE;
  		skb->data[3] &= X25_EXT_M_BIT;
  		skb->data[3] |= (x25->vr << 1) & 0xFE;
  	} else {
  		skb->data[2] &= X25_STD_M_BIT;
  		skb->data[2] |= (x25->vs << 1) & 0x0E;
  		skb->data[2] |= (x25->vr << 5) & 0xE0;
  	}
  
  	x25_transmit_link(skb, x25->neighbour);
  }
  
  void x25_kick(struct sock *sk)
  {
  	struct sk_buff *skb, *skbn;
  	unsigned short start, end;
  	int modulus;
  	struct x25_sock *x25 = x25_sk(sk);
  
  	if (x25->state != X25_STATE_3)
  		return;
  
  	/*
  	 *	Transmit interrupt data.
  	 */
  	if (skb_peek(&x25->interrupt_out_queue) != NULL &&
  		!test_and_set_bit(X25_INTERRUPT_FLAG, &x25->flags)) {
  
  		skb = skb_dequeue(&x25->interrupt_out_queue);
  		x25_transmit_link(skb, x25->neighbour);
  	}
  
  	if (x25->condition & X25_COND_PEER_RX_BUSY)
  		return;
  
  	if (!skb_peek(&sk->sk_write_queue))
  		return;
  
  	modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;
  
  	start   = skb_peek(&x25->ack_queue) ? x25->vs : x25->va;
  	end     = (x25->va + x25->facilities.winsize_out) % modulus;
  
  	if (start == end)
  		return;
  
  	x25->vs = start;
  
  	/*
  	 * Transmit data until either we're out of data to send or
  	 * the window is full.
  	 */
  
  	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.
  		 */
  		x25_send_iframe(sk, skbn);
  
  		x25->vs = (x25->vs + 1) % modulus;
  
  		/*
  		 * Requeue the original data frame.
  		 */
  		skb_queue_tail(&x25->ack_queue, skb);
  
  	} while (x25->vs != end &&
  		 (skb = skb_dequeue(&sk->sk_write_queue)) != NULL);
  
  	x25->vl         = x25->vr;
  	x25->condition &= ~X25_COND_ACK_PENDING;
  
  	x25_stop_timer(sk);
  }
  
  /*
   * The following routines are taken from page 170 of the 7th ARRL Computer
   * Networking Conference paper, as is the whole state machine.
   */
  
  void x25_enquiry_response(struct sock *sk)
  {
  	struct x25_sock *x25 = x25_sk(sk);
  
  	if (x25->condition & X25_COND_OWN_RX_BUSY)
  		x25_write_internal(sk, X25_RNR);
  	else
  		x25_write_internal(sk, X25_RR);
  
  	x25->vl         = x25->vr;
  	x25->condition &= ~X25_COND_ACK_PENDING;
  
  	x25_stop_timer(sk);
  }