net/batman-adv/bitarray.c

/*
 * 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 bat_bitmap_shift_left(unsigned long *seq_bits, int32_t n)
{
	if (n <= 0 || n >= TQ_LOCAL_WINDOW_SIZE)
		return;

	bitmap_shift_left(seq_bits, seq_bits, n, 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 bit_get_packet(void *priv, unsigned long *seq_bits,
		    int32_t seq_num_diff, int set_mark)
{
	struct bat_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 > -TQ_LOCAL_WINDOW_SIZE)) {
		if (set_mark)
			bat_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 < TQ_LOCAL_WINDOW_SIZE)) {
		bat_bitmap_shift_left(seq_bits, seq_num_diff);

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

	/* sequence number is much newer, probably missed a lot of packets */

	if ((seq_num_diff >= TQ_LOCAL_WINDOW_SIZE) &&
	    (seq_num_diff < EXPECTED_SEQNO_RANGE)) {
		bat_dbg(DBG_BATMAN, bat_priv,
			"We missed a lot of packets (%i) !\n",
			seq_num_diff - 1);
		bitmap_zero(seq_bits, TQ_LOCAL_WINDOW_SIZE);
		if (set_mark)
			bat_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 <= -TQ_LOCAL_WINDOW_SIZE) ||
	    (seq_num_diff >= EXPECTED_SEQNO_RANGE)) {

		bat_dbg(DBG_BATMAN, bat_priv,
			"Other host probably restarted!\n");

		bitmap_zero(seq_bits, TQ_LOCAL_WINDOW_SIZE);
		if (set_mark)
			bat_set_bit(seq_bits, 0);

		return 1;
	}

	/* never reached */
	return 0;
}