// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 * 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 <linux/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);
                }
        }
}