bitarray.c

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/* Copyright (C) 2006-2012 B.A.T.M.A.N. contributors:
 *
 * Simon Wunderlich, Marek Lindner
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 */

#include "main.h"
#include "bitarray.h"

#include <linux/bitops.h>

/* shift the packet array by n places. */
static void batadv_bitmap_shift_left(unsigned long *seq_bits, int32_t n)
{
    if (n <= 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE)
        return;

    bitmap_shift_left(seq_bits, seq_bits, n, BATADV_TQ_LOCAL_WINDOW_SIZE);
}


/* receive and process one packet within the sequence number window.
 *
 * returns:
 *  1 if the window was moved (either new or very old)
 *  0 if the window was not moved/shifted.
 */
int batadv_bit_get_packet(void *priv, unsigned long *seq_bits,
              int32_t seq_num_diff, int set_mark)
{
    struct batadv_priv *bat_priv = priv;

    /* sequence number is slightly older. We already got a sequence number
     * higher than this one, so we just mark it.
     */
    if (seq_num_diff <= 0 && seq_num_diff > -BATADV_TQ_LOCAL_WINDOW_SIZE) {
        if (set_mark)
            batadv_set_bit(seq_bits, -seq_num_diff);
        return 0;
    }

    /* sequence number is slightly newer, so we shift the window and
     * set the mark if required
     */
    if (seq_num_diff > 0 && seq_num_diff < BATADV_TQ_LOCAL_WINDOW_SIZE) {
        batadv_bitmap_shift_left(seq_bits, seq_num_diff);

        if (set_mark)
            batadv_set_bit(seq_bits, 0);
        return 1;
    }

    /* sequence number is much newer, probably missed a lot of packets */
    if (seq_num_diff >= BATADV_TQ_LOCAL_WINDOW_SIZE &&
        seq_num_diff < BATADV_EXPECTED_SEQNO_RANGE) {
        batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
               "We missed a lot of packets (%i) !\n",
               seq_num_diff - 1);
        bitmap_zero(seq_bits, BATADV_TQ_LOCAL_WINDOW_SIZE);
        if (set_mark)
            batadv_set_bit(seq_bits, 0);
        return 1;
    }

    /* received a much older packet. The other host either restarted
     * or the old packet got delayed somewhere in the network. The
     * packet should be dropped without calling this function if the
     * seqno window is protected.
     */
    if (seq_num_diff <= -BATADV_TQ_LOCAL_WINDOW_SIZE ||
        seq_num_diff >= BATADV_EXPECTED_SEQNO_RANGE) {

        batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
               "Other host probably restarted!\n");

        bitmap_zero(seq_bits, BATADV_TQ_LOCAL_WINDOW_SIZE);
        if (set_mark)
            batadv_set_bit(seq_bits, 0);

        return 1;
    }

    /* never reached */
    return 0;
}