// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      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
 *
 *      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\n", 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);
}