// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   *	LAPB release 002
   *
   *	This code REQUIRES 2.1.15 or higher/ NET3.038
   *

   *	History
   *	LAPB 001	Jonathan Naylor	Started Coding
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #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/inet.h>
  #include <linux/skbuff.h>

  #include <linux/slab.h>

  #include <net/sock.h>

  #include <linux/uaccess.h>

  #include <linux/fcntl.h>
  #include <linux/mm.h>
  #include <linux/interrupt.h>
  #include <net/lapb.h>
  
  /*
   *	This routine purges all the queues of frames.
   */
  void lapb_clear_queues(struct lapb_cb *lapb)
  {
  	skb_queue_purge(&lapb->write_queue);
  	skb_queue_purge(&lapb->ack_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 lapb_frames_acked(struct lapb_cb *lapb, unsigned short nr)
  {
  	struct sk_buff *skb;
  	int modulus;
  
  	modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS;
  
  	/*
  	 * Remove all the ack-ed frames from the ack queue.
  	 */
  	if (lapb->va != nr)
  		while (skb_peek(&lapb->ack_queue) && lapb->va != nr) {

  			skb = skb_dequeue(&lapb->ack_queue);

  			kfree_skb(skb);
  			lapb->va = (lapb->va + 1) % modulus;
  		}
  }
  
  void lapb_requeue_frames(struct lapb_cb *lapb)
  {

  	struct sk_buff *skb, *skb_prev = NULL;

  
  	/*
  	 * Requeue all the un-ack-ed frames on the output queue to be picked
  	 * up by lapb_kick called from the timer. This arrangement handles the
  	 * possibility of an empty output queue.
  	 */
  	while ((skb = skb_dequeue(&lapb->ack_queue)) != NULL) {
  		if (!skb_prev)
  			skb_queue_head(&lapb->write_queue, skb);
  		else

  			skb_append(skb_prev, skb, &lapb->write_queue);

  		skb_prev = skb;
  	}
  }
  
  /*
   *	Validate that the value of nr is between va and vs. Return true or
   *	false for testing.
   */
  int lapb_validate_nr(struct lapb_cb *lapb, unsigned short nr)
  {
  	unsigned short vc = lapb->va;
  	int modulus;

  	modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS;
  
  	while (vc != lapb->vs) {
  		if (nr == vc)
  			return 1;
  		vc = (vc + 1) % modulus;
  	}

  	return nr == lapb->vs;
  }
  
  /*
   *	This routine is the centralised routine for parsing the control
   *	information for the different frame formats.
   */
  int lapb_decode(struct lapb_cb *lapb, struct sk_buff *skb,
  		struct lapb_frame *frame)
  {
  	frame->type = LAPB_ILLEGAL;

  	lapb_dbg(2, "(%p) S%d RX %3ph
  ", lapb->dev, lapb->state, skb->data);

  
  	/* We always need to look at 2 bytes, sometimes we need
  	 * to look at 3 and those cases are handled below.
  	 */
  	if (!pskb_may_pull(skb, 2))
  		return -1;
  
  	if (lapb->mode & LAPB_MLP) {
  		if (lapb->mode & LAPB_DCE) {
  			if (skb->data[0] == LAPB_ADDR_D)
  				frame->cr = LAPB_COMMAND;
  			if (skb->data[0] == LAPB_ADDR_C)
  				frame->cr = LAPB_RESPONSE;
  		} else {
  			if (skb->data[0] == LAPB_ADDR_C)
  				frame->cr = LAPB_COMMAND;
  			if (skb->data[0] == LAPB_ADDR_D)
  				frame->cr = LAPB_RESPONSE;
  		}
  	} else {
  		if (lapb->mode & LAPB_DCE) {
  			if (skb->data[0] == LAPB_ADDR_B)
  				frame->cr = LAPB_COMMAND;
  			if (skb->data[0] == LAPB_ADDR_A)
  				frame->cr = LAPB_RESPONSE;
  		} else {
  			if (skb->data[0] == LAPB_ADDR_A)
  				frame->cr = LAPB_COMMAND;
  			if (skb->data[0] == LAPB_ADDR_B)
  				frame->cr = LAPB_RESPONSE;
  		}
  	}

  	skb_pull(skb, 1);
  
  	if (lapb->mode & LAPB_EXTENDED) {
  		if (!(skb->data[0] & LAPB_S)) {
  			if (!pskb_may_pull(skb, 2))
  				return -1;
  			/*
  			 * I frame - carries NR/NS/PF
  			 */
  			frame->type       = LAPB_I;
  			frame->ns         = (skb->data[0] >> 1) & 0x7F;
  			frame->nr         = (skb->data[1] >> 1) & 0x7F;
  			frame->pf         = skb->data[1] & LAPB_EPF;
  			frame->control[0] = skb->data[0];
  			frame->control[1] = skb->data[1];
  			skb_pull(skb, 2);
  		} else if ((skb->data[0] & LAPB_U) == 1) {
  			if (!pskb_may_pull(skb, 2))
  				return -1;
  			/*
  			 * S frame - take out PF/NR
  			 */
  			frame->type       = skb->data[0] & 0x0F;
  			frame->nr         = (skb->data[1] >> 1) & 0x7F;
  			frame->pf         = skb->data[1] & LAPB_EPF;
  			frame->control[0] = skb->data[0];
  			frame->control[1] = skb->data[1];
  			skb_pull(skb, 2);
  		} else if ((skb->data[0] & LAPB_U) == 3) {
  			/*
  			 * U frame - take out PF
  			 */
  			frame->type       = skb->data[0] & ~LAPB_SPF;
  			frame->pf         = skb->data[0] & LAPB_SPF;
  			frame->control[0] = skb->data[0];
  			frame->control[1] = 0x00;
  			skb_pull(skb, 1);
  		}
  	} else {
  		if (!(skb->data[0] & LAPB_S)) {
  			/*
  			 * I frame - carries NR/NS/PF
  			 */
  			frame->type = LAPB_I;
  			frame->ns   = (skb->data[0] >> 1) & 0x07;
  			frame->nr   = (skb->data[0] >> 5) & 0x07;
  			frame->pf   = skb->data[0] & LAPB_SPF;
  		} else if ((skb->data[0] & LAPB_U) == 1) {
  			/*
  			 * S frame - take out PF/NR
  			 */
  			frame->type = skb->data[0] & 0x0F;
  			frame->nr   = (skb->data[0] >> 5) & 0x07;
  			frame->pf   = skb->data[0] & LAPB_SPF;
  		} else if ((skb->data[0] & LAPB_U) == 3) {
  			/*
  			 * U frame - take out PF
  			 */
  			frame->type = skb->data[0] & ~LAPB_SPF;
  			frame->pf   = skb->data[0] & LAPB_SPF;
  		}
  
  		frame->control[0] = skb->data[0];
  
  		skb_pull(skb, 1);
  	}
  
  	return 0;
  }

  /*

   *	This routine is called when the HDLC layer internally  generates a

   *	command or  response  for  the remote machine ( eg. RR, UA etc. ).

   *	Only supervisory or unnumbered frames are processed, FRMRs are handled
   *	by lapb_transmit_frmr below.
   */
  void lapb_send_control(struct lapb_cb *lapb, int frametype,
  		       int poll_bit, int type)
  {
  	struct sk_buff *skb;
  	unsigned char  *dptr;
  
  	if ((skb = alloc_skb(LAPB_HEADER_LEN + 3, GFP_ATOMIC)) == NULL)
  		return;
  
  	skb_reserve(skb, LAPB_HEADER_LEN + 1);
  
  	if (lapb->mode & LAPB_EXTENDED) {
  		if ((frametype & LAPB_U) == LAPB_U) {
  			dptr   = skb_put(skb, 1);
  			*dptr  = frametype;
  			*dptr |= poll_bit ? LAPB_SPF : 0;
  		} else {
  			dptr     = skb_put(skb, 2);
  			dptr[0]  = frametype;
  			dptr[1]  = (lapb->vr << 1);
  			dptr[1] |= poll_bit ? LAPB_EPF : 0;
  		}
  	} else {
  		dptr   = skb_put(skb, 1);
  		*dptr  = frametype;
  		*dptr |= poll_bit ? LAPB_SPF : 0;
  		if ((frametype & LAPB_U) == LAPB_S)	/* S frames carry NR */
  			*dptr |= (lapb->vr << 5);
  	}
  
  	lapb_transmit_buffer(lapb, skb, type);
  }

  /*

   *	This routine generates FRMRs based on information previously stored in
   *	the LAPB control block.
   */
  void lapb_transmit_frmr(struct lapb_cb *lapb)
  {
  	struct sk_buff *skb;
  	unsigned char  *dptr;
  
  	if ((skb = alloc_skb(LAPB_HEADER_LEN + 7, GFP_ATOMIC)) == NULL)
  		return;
  
  	skb_reserve(skb, LAPB_HEADER_LEN + 1);
  
  	if (lapb->mode & LAPB_EXTENDED) {
  		dptr    = skb_put(skb, 6);
  		*dptr++ = LAPB_FRMR;
  		*dptr++ = lapb->frmr_data.control[0];
  		*dptr++ = lapb->frmr_data.control[1];
  		*dptr++ = (lapb->vs << 1) & 0xFE;
  		*dptr   = (lapb->vr << 1) & 0xFE;
  		if (lapb->frmr_data.cr == LAPB_RESPONSE)
  			*dptr |= 0x01;
  		dptr++;
  		*dptr++ = lapb->frmr_type;

  		lapb_dbg(1, "(%p) S%d TX FRMR %5ph
  ",

  			 lapb->dev, lapb->state,

  			 &skb->data[1]);

  	} else {
  		dptr    = skb_put(skb, 4);
  		*dptr++ = LAPB_FRMR;
  		*dptr++ = lapb->frmr_data.control[0];
  		*dptr   = (lapb->vs << 1) & 0x0E;
  		*dptr  |= (lapb->vr << 5) & 0xE0;
  		if (lapb->frmr_data.cr == LAPB_RESPONSE)
  			*dptr |= 0x10;
  		dptr++;
  		*dptr++ = lapb->frmr_type;

  		lapb_dbg(1, "(%p) S%d TX FRMR %3ph
  ",
  			 lapb->dev, lapb->state, &skb->data[1]);

  	}
  
  	lapb_transmit_buffer(lapb, skb, LAPB_RESPONSE);
  }