// 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\n", 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\n",
                         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\n",
                         lapb->dev, lapb->state, &skb->data[1]);
        }

        lapb_transmit_buffer(lapb, skb, LAPB_RESPONSE);
}