x25_out.c

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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/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);
}