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/*

 *      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 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/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) {

                        if ((skbn = sock_alloc_send_skb(sk, frontlen + max_len,

                                                        noblock, &err)) == NULL){

                                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 (!x25->intflag && skb_peek(&x25->interrupt_out_queue) != NULL) {

                x25->intflag = 1;

                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);

}