// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) B.A.T.M.A.N. contributors:
 *
 * Simon Wunderlich, Marek Lindner
 */

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

#include <linux/bitmap.h>

#include "log.h"

/* shift the packet array by n places. */
static void batadv_bitmap_shift_left(unsigned long *seq_bits, s32 n)
{
        if (n <= 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE)
                return;

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

/**
 * batadv_bit_get_packet() - receive and process one packet within the sequence
 *  number window
 * @priv: the bat priv with all the mesh interface information
 * @seq_bits: pointer to the sequence number receive packet
 * @seq_num_diff: difference between the current/received sequence number and
 *  the last sequence number
 * @set_mark: whether this packet should be marked in seq_bits
 *
 * Return: true if the window was moved (either new or very old),
 *  false if the window was not moved/shifted.
 */
bool batadv_bit_get_packet(void *priv, unsigned long *seq_bits,
                           s32 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 false;
        }

        /* 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 true;
        }

        /* 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 true;
        }

        /* 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.
         *
         * seq_num_diff <= -BATADV_TQ_LOCAL_WINDOW_SIZE
         * or
         * 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 true;
}