net/x25/x25_subr.c - linux-mtk - Git at Google

 /*
  *	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	  Centralised disconnection processing.
  *	mar/20/00	Daniela Squassoni Disabling/enabling of facilities
  *					  negotiation.
  *	jun/24/01	Arnaldo C. Melo	  use skb_queue_purge, cleanups
  *	apr/04/15	Shaun Pereira		Fast select with no
  *						restriction on response.
  */

 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/skbuff.h>
 #include <net/sock.h>
 #include <net/tcp.h>
 #include <net/x25.h>

 /*
  *	This routine purges all of the queues of frames.
  */
 void x25_clear_queues(struct sock *sk)
 {
 	struct x25_sock *x25 = x25_sk(sk);

 	skb_queue_purge(&sk->sk_write_queue);
 	skb_queue_purge(&x25->ack_queue);
 	skb_queue_purge(&x25->interrupt_in_queue);
 	skb_queue_purge(&x25->interrupt_out_queue);
 	skb_queue_purge(&x25->fragment_queue);
 }


 /*
  * This routine purges the input queue of those frames that have been
  * acknowledged. This replaces the boxes labelled "V(a) <- N(r)" on the
  * SDL diagram.
 */
 void x25_frames_acked(struct sock *sk, unsigned short nr)
 {
 	struct sk_buff *skb;
 	struct x25_sock *x25 = x25_sk(sk);
 	int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

 	/*
 	 * Remove all the ack-ed frames from the ack queue.
 	 */
 	if (x25->va != nr)
 		while (skb_peek(&x25->ack_queue) && x25->va != nr) {
 			skb = skb_dequeue(&x25->ack_queue);
 			kfree_skb(skb);
 			x25->va = (x25->va + 1) % modulus;
 		}
 }

 void x25_requeue_frames(struct sock *sk)
 {
 	struct sk_buff *skb, *skb_prev = NULL;

 	/*
 	 * Requeue all the un-ack-ed frames on the output queue to be picked
 	 * up by x25_kick. This arrangement handles the possibility of an empty
 	 * output queue.
 	 */
 	while ((skb = skb_dequeue(&x25_sk(sk)->ack_queue)) != NULL) {
 		if (!skb_prev)
 			skb_queue_head(&sk->sk_write_queue, skb);
 		else
 			skb_append(skb_prev, skb, &sk->sk_write_queue);
 		skb_prev = skb;
 	}
 }

 /*
  *	Validate that the value of nr is between va and vs. Return true or
  *	false for testing.
  */
 int x25_validate_nr(struct sock *sk, unsigned short nr)
 {
 	struct x25_sock *x25 = x25_sk(sk);
 	unsigned short vc = x25->va;
 	int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

 	while (vc != x25->vs) {
 		if (nr == vc)
 			return 1;
 		vc = (vc + 1) % modulus;
 	}

 	return nr == x25->vs ? 1 : 0;
 }

 /*
  *  This routine is called when the packet layer internally generates a
  *  control frame.
  */
 void x25_write_internal(struct sock *sk, int frametype)
 {
 	struct x25_sock *x25 = x25_sk(sk);
 	struct sk_buff *skb;
 	unsigned char  *dptr;
 	unsigned char  facilities[X25_MAX_FAC_LEN];
 	unsigned char  addresses[1 + X25_ADDR_LEN];
 	unsigned char  lci1, lci2;
 	/*
 	 *	Default safe frame size.
 	 */
 	int len = X25_MAX_L2_LEN + X25_EXT_MIN_LEN;

 	/*
 	 *	Adjust frame size.
 	 */
 	switch (frametype) {
 		case X25_CALL_REQUEST:
 			len += 1 + X25_ADDR_LEN + X25_MAX_FAC_LEN +
 			       X25_MAX_CUD_LEN;
 			break;
 		case X25_CALL_ACCEPTED: /* fast sel with no restr on resp */
 			if(x25->facilities.reverse & 0x80) {
 				len += 1 + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
 			} else {
 				len += 1 + X25_MAX_FAC_LEN;
 			}
 			break;
 		case X25_CLEAR_REQUEST:
 		case X25_RESET_REQUEST:
 			len += 2;
 			break;
 		case X25_RR:
 		case X25_RNR:
 		case X25_REJ:
 		case X25_CLEAR_CONFIRMATION:
 		case X25_INTERRUPT_CONFIRMATION:
 		case X25_RESET_CONFIRMATION:
 			break;
 		default:
 			printk(KERN_ERR "X.25: invalid frame type %02X\n",
 			       frametype);
 			return;
 	}

 	if ((skb = alloc_skb(len, GFP_ATOMIC)) == NULL)
 		return;

 	/*
 	 *	Space for Ethernet and 802.2 LLC headers.
 	 */
 	skb_reserve(skb, X25_MAX_L2_LEN);

 	/*
 	 *	Make space for the GFI and LCI, and fill them in.
 	 */
 	dptr = skb_put(skb, 2);

 	lci1 = (x25->lci >> 8) & 0x0F;
 	lci2 = (x25->lci >> 0) & 0xFF;

 	if (x25->neighbour->extended) {
 		*dptr++ = lci1 | X25_GFI_EXTSEQ;
 		*dptr++ = lci2;
 	} else {
 		*dptr++ = lci1 | X25_GFI_STDSEQ;
 		*dptr++ = lci2;
 	}

 	/*
 	 *	Now fill in the frame type specific information.
 	 */
 	switch (frametype) {

 		case X25_CALL_REQUEST:
 			dptr    = skb_put(skb, 1);
 			*dptr++ = X25_CALL_REQUEST;
 			len     = x25_addr_aton(addresses, &x25->dest_addr,
 						&x25->source_addr);
 			dptr    = skb_put(skb, len);
 			memcpy(dptr, addresses, len);
 			len     = x25_create_facilities(facilities,
 							&x25->facilities,
 					     x25->neighbour->global_facil_mask);
 			dptr    = skb_put(skb, len);
 			memcpy(dptr, facilities, len);
 			dptr = skb_put(skb, x25->calluserdata.cudlength);
 			memcpy(dptr, x25->calluserdata.cuddata,
 			       x25->calluserdata.cudlength);
 			x25->calluserdata.cudlength = 0;
 			break;

 		case X25_CALL_ACCEPTED:
 			dptr    = skb_put(skb, 2);
 			*dptr++ = X25_CALL_ACCEPTED;
 			*dptr++ = 0x00;		/* Address lengths */
 			len     = x25_create_facilities(facilities,
 							&x25->facilities,
 							x25->vc_facil_mask);
 			dptr    = skb_put(skb, len);
 			memcpy(dptr, facilities, len);

 			/* fast select with no restriction on response
 				allows call user data. Userland must
 				ensure it is ours and not theirs */
 			if(x25->facilities.reverse & 0x80) {
 				dptr = skb_put(skb,
 					x25->calluserdata.cudlength);
 				memcpy(dptr, x25->calluserdata.cuddata,
 				       x25->calluserdata.cudlength);
 			}
 			x25->calluserdata.cudlength = 0;
 			break;

 		case X25_CLEAR_REQUEST:
 		case X25_RESET_REQUEST:
 			dptr    = skb_put(skb, 3);
 			*dptr++ = frametype;
 			*dptr++ = 0x00;		/* XXX */
 			*dptr++ = 0x00;		/* XXX */
 			break;

 		case X25_RR:
 		case X25_RNR:
 		case X25_REJ:
 			if (x25->neighbour->extended) {
 				dptr     = skb_put(skb, 2);
 				*dptr++  = frametype;
 				*dptr++  = (x25->vr << 1) & 0xFE;
 			} else {
 				dptr     = skb_put(skb, 1);
 				*dptr    = frametype;
 				*dptr++ |= (x25->vr << 5) & 0xE0;
 			}
 			break;

 		case X25_CLEAR_CONFIRMATION:
 		case X25_INTERRUPT_CONFIRMATION:
 		case X25_RESET_CONFIRMATION:
 			dptr  = skb_put(skb, 1);
 			*dptr = frametype;
 			break;
 	}

 	x25_transmit_link(skb, x25->neighbour);
 }

 /*
  *	Unpick the contents of the passed X.25 Packet Layer frame.
  */
 int x25_decode(struct sock *sk, struct sk_buff *skb, int *ns, int *nr, int *q,
 	       int *d, int *m)
 {
 	struct x25_sock *x25 = x25_sk(sk);
 	unsigned char *frame = skb->data;

 	*ns = *nr = *q = *d = *m = 0;

 	switch (frame[2]) {
 		case X25_CALL_REQUEST:
 		case X25_CALL_ACCEPTED:
 		case X25_CLEAR_REQUEST:
 		case X25_CLEAR_CONFIRMATION:
 		case X25_INTERRUPT:
 		case X25_INTERRUPT_CONFIRMATION:
 		case X25_RESET_REQUEST:
 		case X25_RESET_CONFIRMATION:
 		case X25_RESTART_REQUEST:
 		case X25_RESTART_CONFIRMATION:
 		case X25_REGISTRATION_REQUEST:
 		case X25_REGISTRATION_CONFIRMATION:
 		case X25_DIAGNOSTIC:
 			return frame[2];
 	}

 	if (x25->neighbour->extended) {
 		if (frame[2] == X25_RR  ||
 		    frame[2] == X25_RNR ||
 		    frame[2] == X25_REJ) {
 			*nr = (frame[3] >> 1) & 0x7F;
 			return frame[2];
 		}
 	} else {
 		if ((frame[2] & 0x1F) == X25_RR  ||
 		    (frame[2] & 0x1F) == X25_RNR ||
 		    (frame[2] & 0x1F) == X25_REJ) {
 			*nr = (frame[2] >> 5) & 0x07;
 			return frame[2] & 0x1F;
 		}
 	}

 	if (x25->neighbour->extended) {
 		if ((frame[2] & 0x01) == X25_DATA) {
 			*q  = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
 			*d  = (frame[0] & X25_D_BIT) == X25_D_BIT;
 			*m  = (frame[3] & X25_EXT_M_BIT) == X25_EXT_M_BIT;
 			*nr = (frame[3] >> 1) & 0x7F;
 			*ns = (frame[2] >> 1) & 0x7F;
 			return X25_DATA;
 		}
 	} else {
 		if ((frame[2] & 0x01) == X25_DATA) {
 			*q  = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
 			*d  = (frame[0] & X25_D_BIT) == X25_D_BIT;
 			*m  = (frame[2] & X25_STD_M_BIT) == X25_STD_M_BIT;
 			*nr = (frame[2] >> 5) & 0x07;
 			*ns = (frame[2] >> 1) & 0x07;
 			return X25_DATA;
 		}
 	}

 	printk(KERN_DEBUG "X.25: invalid PLP frame %02X %02X %02X\n",
 	       frame[0], frame[1], frame[2]);

 	return X25_ILLEGAL;
 }

 void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
 		    unsigned char diagnostic)
 {
 	struct x25_sock *x25 = x25_sk(sk);

 	x25_clear_queues(sk);
 	x25_stop_timer(sk);

 	x25->lci   = 0;
 	x25->state = X25_STATE_0;

 	x25->causediag.cause      = cause;
 	x25->causediag.diagnostic = diagnostic;

 	sk->sk_state     = TCP_CLOSE;
 	sk->sk_err       = reason;
 	sk->sk_shutdown |= SEND_SHUTDOWN;

 	if (!sock_flag(sk, SOCK_DEAD)) {
 		sk->sk_state_change(sk);
 		sock_set_flag(sk, SOCK_DEAD);
 	}
 }

 /*
  * Clear an own-rx-busy condition and tell the peer about this, provided
  * that there is a significant amount of free receive buffer space available.
  */
 void x25_check_rbuf(struct sock *sk)
 {
 	struct x25_sock *x25 = x25_sk(sk);

 	if (atomic_read(&sk->sk_rmem_alloc) < (sk->sk_rcvbuf / 2) &&
 	    (x25->condition & X25_COND_OWN_RX_BUSY)) {
 		x25->condition &= ~X25_COND_OWN_RX_BUSY;
 		x25->condition &= ~X25_COND_ACK_PENDING;
 		x25->vl         = x25->vr;
 		x25_write_internal(sk, X25_RR);
 		x25_stop_timer(sk);
 	}
 }
	/*
	* 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 Centralised disconnection processing.
	* mar/20/00 Daniela Squassoni Disabling/enabling of facilities
	* negotiation.
	* jun/24/01 Arnaldo C. Melo use skb_queue_purge, cleanups
	* apr/04/15 Shaun Pereira Fast select with no
	* restriction on response.
	*/

	#include <linux/kernel.h>
	#include <linux/string.h>
	#include <linux/skbuff.h>
	#include <net/sock.h>
	#include <net/tcp.h>
	#include <net/x25.h>

	/*
	* This routine purges all of the queues of frames.
	*/
	void x25_clear_queues(struct sock *sk)
	{
	struct x25_sock *x25 = x25_sk(sk);

	skb_queue_purge(&sk->sk_write_queue);
	skb_queue_purge(&x25->ack_queue);
	skb_queue_purge(&x25->interrupt_in_queue);
	skb_queue_purge(&x25->interrupt_out_queue);
	skb_queue_purge(&x25->fragment_queue);
	}


	/*
	* This routine purges the input queue of those frames that have been
	* acknowledged. This replaces the boxes labelled "V(a) <- N(r)" on the
	* SDL diagram.
	*/
	void x25_frames_acked(struct sock *sk, unsigned short nr)
	{
	struct sk_buff *skb;
	struct x25_sock *x25 = x25_sk(sk);
	int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

	/*
	* Remove all the ack-ed frames from the ack queue.
	*/
	if (x25->va != nr)
	while (skb_peek(&x25->ack_queue) && x25->va != nr) {
	skb = skb_dequeue(&x25->ack_queue);
	kfree_skb(skb);
	x25->va = (x25->va + 1) % modulus;
	}
	}

	void x25_requeue_frames(struct sock *sk)
	{
	struct sk_buff skb, skb_prev = NULL;

	/*
	* Requeue all the un-ack-ed frames on the output queue to be picked
	* up by x25_kick. This arrangement handles the possibility of an empty
	* output queue.
	*/
	while ((skb = skb_dequeue(&x25_sk(sk)->ack_queue)) != NULL) {
	if (!skb_prev)
	skb_queue_head(&sk->sk_write_queue, skb);
	else
	skb_append(skb_prev, skb, &sk->sk_write_queue);
	skb_prev = skb;
	}
	}

	/*
	* Validate that the value of nr is between va and vs. Return true or
	* false for testing.
	*/
	int x25_validate_nr(struct sock *sk, unsigned short nr)
	{
	struct x25_sock *x25 = x25_sk(sk);
	unsigned short vc = x25->va;
	int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

	while (vc != x25->vs) {
	if (nr == vc)
	return 1;
	vc = (vc + 1) % modulus;
	}

	return nr == x25->vs ? 1 : 0;
	}

	/*
	* This routine is called when the packet layer internally generates a
	* control frame.
	*/
	void x25_write_internal(struct sock *sk, int frametype)
	{
	struct x25_sock *x25 = x25_sk(sk);
	struct sk_buff *skb;
	unsigned char *dptr;
	unsigned char facilities[X25_MAX_FAC_LEN];
	unsigned char addresses[1 + X25_ADDR_LEN];
	unsigned char lci1, lci2;
	/*
	* Default safe frame size.
	*/
	int len = X25_MAX_L2_LEN + X25_EXT_MIN_LEN;

	/*
	* Adjust frame size.
	*/
	switch (frametype) {
	case X25_CALL_REQUEST:
	len += 1 + X25_ADDR_LEN + X25_MAX_FAC_LEN +
	X25_MAX_CUD_LEN;
	break;
	case X25_CALL_ACCEPTED: /* fast sel with no restr on resp */
	if(x25->facilities.reverse & 0x80) {
	len += 1 + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
	} else {
	len += 1 + X25_MAX_FAC_LEN;
	}
	break;
	case X25_CLEAR_REQUEST:
	case X25_RESET_REQUEST:
	len += 2;
	break;
	case X25_RR:
	case X25_RNR:
	case X25_REJ:
	case X25_CLEAR_CONFIRMATION:
	case X25_INTERRUPT_CONFIRMATION:
	case X25_RESET_CONFIRMATION:
	break;
	default:
	printk(KERN_ERR "X.25: invalid frame type %02X\n",
	frametype);
	return;
	}

	if ((skb = alloc_skb(len, GFP_ATOMIC)) == NULL)
	return;

	/*
	* Space for Ethernet and 802.2 LLC headers.
	*/
	skb_reserve(skb, X25_MAX_L2_LEN);

	/*
	* Make space for the GFI and LCI, and fill them in.
	*/
	dptr = skb_put(skb, 2);

	lci1 = (x25->lci >> 8) & 0x0F;
	lci2 = (x25->lci >> 0) & 0xFF;

	if (x25->neighbour->extended) {
	*dptr++ = lci1 \| X25_GFI_EXTSEQ;
	*dptr++ = lci2;
	} else {
	*dptr++ = lci1 \| X25_GFI_STDSEQ;
	*dptr++ = lci2;
	}

	/*
	* Now fill in the frame type specific information.
	*/
	switch (frametype) {

	case X25_CALL_REQUEST:
	dptr = skb_put(skb, 1);
	*dptr++ = X25_CALL_REQUEST;
	len = x25_addr_aton(addresses, &x25->dest_addr,
	&x25->source_addr);
	dptr = skb_put(skb, len);
	memcpy(dptr, addresses, len);
	len = x25_create_facilities(facilities,
	&x25->facilities,
	x25->neighbour->global_facil_mask);
	dptr = skb_put(skb, len);
	memcpy(dptr, facilities, len);
	dptr = skb_put(skb, x25->calluserdata.cudlength);
	memcpy(dptr, x25->calluserdata.cuddata,
	x25->calluserdata.cudlength);
	x25->calluserdata.cudlength = 0;
	break;

	case X25_CALL_ACCEPTED:
	dptr = skb_put(skb, 2);
	*dptr++ = X25_CALL_ACCEPTED;
	dptr++ = 0x00; / Address lengths */
	len = x25_create_facilities(facilities,
	&x25->facilities,
	x25->vc_facil_mask);
	dptr = skb_put(skb, len);
	memcpy(dptr, facilities, len);

	/* fast select with no restriction on response
	allows call user data. Userland must
	ensure it is ours and not theirs */
	if(x25->facilities.reverse & 0x80) {
	dptr = skb_put(skb,
	x25->calluserdata.cudlength);
	memcpy(dptr, x25->calluserdata.cuddata,
	x25->calluserdata.cudlength);
	}
	x25->calluserdata.cudlength = 0;
	break;

	case X25_CLEAR_REQUEST:
	case X25_RESET_REQUEST:
	dptr = skb_put(skb, 3);
	*dptr++ = frametype;
	dptr++ = 0x00; / XXX */
	dptr++ = 0x00; / XXX */
	break;

	case X25_RR:
	case X25_RNR:
	case X25_REJ:
	if (x25->neighbour->extended) {
	dptr = skb_put(skb, 2);
	*dptr++ = frametype;
	*dptr++ = (x25->vr << 1) & 0xFE;
	} else {
	dptr = skb_put(skb, 1);
	*dptr = frametype;
	*dptr++ \|= (x25->vr << 5) & 0xE0;
	}
	break;

	case X25_CLEAR_CONFIRMATION:
	case X25_INTERRUPT_CONFIRMATION:
	case X25_RESET_CONFIRMATION:
	dptr = skb_put(skb, 1);
	*dptr = frametype;
	break;
	}

	x25_transmit_link(skb, x25->neighbour);
	}

	/*
	* Unpick the contents of the passed X.25 Packet Layer frame.
	*/
	int x25_decode(struct sock sk, struct sk_buff skb, int ns, int nr, int *q,
	int d, int m)
	{
	struct x25_sock *x25 = x25_sk(sk);
	unsigned char *frame = skb->data;

	ns = nr = q = d = *m = 0;

	switch (frame[2]) {
	case X25_CALL_REQUEST:
	case X25_CALL_ACCEPTED:
	case X25_CLEAR_REQUEST:
	case X25_CLEAR_CONFIRMATION:
	case X25_INTERRUPT:
	case X25_INTERRUPT_CONFIRMATION:
	case X25_RESET_REQUEST:
	case X25_RESET_CONFIRMATION:
	case X25_RESTART_REQUEST:
	case X25_RESTART_CONFIRMATION:
	case X25_REGISTRATION_REQUEST:
	case X25_REGISTRATION_CONFIRMATION:
	case X25_DIAGNOSTIC:
	return frame[2];
	}

	if (x25->neighbour->extended) {
	if (frame[2] == X25_RR \|\|
	frame[2] == X25_RNR \|\|
	frame[2] == X25_REJ) {
	*nr = (frame[3] >> 1) & 0x7F;
	return frame[2];
	}
	} else {
	if ((frame[2] & 0x1F) == X25_RR \|\|
	(frame[2] & 0x1F) == X25_RNR \|\|
	(frame[2] & 0x1F) == X25_REJ) {
	*nr = (frame[2] >> 5) & 0x07;
	return frame[2] & 0x1F;
	}
	}

	if (x25->neighbour->extended) {
	if ((frame[2] & 0x01) == X25_DATA) {
	*q = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
	*d = (frame[0] & X25_D_BIT) == X25_D_BIT;
	*m = (frame[3] & X25_EXT_M_BIT) == X25_EXT_M_BIT;
	*nr = (frame[3] >> 1) & 0x7F;
	*ns = (frame[2] >> 1) & 0x7F;
	return X25_DATA;
	}
	} else {
	if ((frame[2] & 0x01) == X25_DATA) {
	*q = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
	*d = (frame[0] & X25_D_BIT) == X25_D_BIT;
	*m = (frame[2] & X25_STD_M_BIT) == X25_STD_M_BIT;
	*nr = (frame[2] >> 5) & 0x07;
	*ns = (frame[2] >> 1) & 0x07;
	return X25_DATA;
	}
	}

	printk(KERN_DEBUG "X.25: invalid PLP frame %02X %02X %02X\n",
	frame[0], frame[1], frame[2]);

	return X25_ILLEGAL;
	}

	void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
	unsigned char diagnostic)
	{
	struct x25_sock *x25 = x25_sk(sk);

	x25_clear_queues(sk);
	x25_stop_timer(sk);

	x25->lci = 0;
	x25->state = X25_STATE_0;

	x25->causediag.cause = cause;
	x25->causediag.diagnostic = diagnostic;

	sk->sk_state = TCP_CLOSE;
	sk->sk_err = reason;
	sk->sk_shutdown \|= SEND_SHUTDOWN;

	if (!sock_flag(sk, SOCK_DEAD)) {
	sk->sk_state_change(sk);
	sock_set_flag(sk, SOCK_DEAD);
	}
	}

	/*
	* Clear an own-rx-busy condition and tell the peer about this, provided
	* that there is a significant amount of free receive buffer space available.
	*/
	void x25_check_rbuf(struct sock *sk)
	{
	struct x25_sock *x25 = x25_sk(sk);

	if (atomic_read(&sk->sk_rmem_alloc) < (sk->sk_rcvbuf / 2) &&
	(x25->condition & X25_COND_OWN_RX_BUSY)) {
	x25->condition &= ~X25_COND_OWN_RX_BUSY;
	x25->condition &= ~X25_COND_ACK_PENDING;
	x25->vl = x25->vr;
	x25_write_internal(sk, X25_RR);
	x25_stop_timer(sk);
	}
	}