// SPDX-License-Identifier: GPL-2.0-or-later
/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001 Intel Corp.
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions manipulate sctp tsn mapping array.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <linux-sctp@vger.kernel.org>
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Jon Grimm             <jgrimm@us.ibm.com>
 *    Karl Knutson          <karl@athena.chicago.il.us>
 *    Sridhar Samudrala     <sri@us.ibm.com>
 */

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/bitmap.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

static void sctp_tsnmap_update(struct sctp_tsnmap *map);
static void sctp_tsnmap_find_gap_ack(unsigned long *map, __u16 off,
                                     __u16 len, __u16 *start, __u16 *end);
static int sctp_tsnmap_grow(struct sctp_tsnmap *map, u16 size);

/* Initialize a block of memory as a tsnmap.  */
struct sctp_tsnmap *sctp_tsnmap_init(struct sctp_tsnmap *map, __u16 len,
                                     __u32 initial_tsn, gfp_t gfp)
{
        if (!map->tsn_map) {
                map->tsn_map = kzalloc(len>>3, gfp);
                if (map->tsn_map == NULL)
                        return NULL;

                map->len = len;
        } else {
                bitmap_zero(map->tsn_map, map->len);
        }

        /* Keep track of TSNs represented by tsn_map.  */
        map->base_tsn = initial_tsn;
        map->cumulative_tsn_ack_point = initial_tsn - 1;
        map->max_tsn_seen = map->cumulative_tsn_ack_point;
        map->num_dup_tsns = 0;

        return map;
}

void sctp_tsnmap_free(struct sctp_tsnmap *map)
{
        map->len = 0;
        kfree(map->tsn_map);
}

/* Test the tracking state of this TSN.
 * Returns:
 *   0 if the TSN has not yet been seen
 *  >0 if the TSN has been seen (duplicate)
 *  <0 if the TSN is invalid (too large to track)
 */
int sctp_tsnmap_check(const struct sctp_tsnmap *map, __u32 tsn)
{
        u32 gap;

        /* Check to see if this is an old TSN */
        if (TSN_lte(tsn, map->cumulative_tsn_ack_point))
                return 1;

        /* Verify that we can hold this TSN and that it will not
         * overflow our map
         */
        if (!TSN_lt(tsn, map->base_tsn + SCTP_TSN_MAP_SIZE))
                return -1;

        /* Calculate the index into the mapping arrays.  */
        gap = tsn - map->base_tsn;

        /* Check to see if TSN has already been recorded.  */
        if (gap < map->len && test_bit(gap, map->tsn_map))
                return 1;
        else
                return 0;
}


/* Mark this TSN as seen.  */
int sctp_tsnmap_mark(struct sctp_tsnmap *map, __u32 tsn,
                     struct sctp_transport *trans)
{
        u16 gap;

        if (TSN_lt(tsn, map->base_tsn))
                return 0;

        gap = tsn - map->base_tsn;

        if (gap >= map->len && !sctp_tsnmap_grow(map, gap + 1))
                return -ENOMEM;

        if (!sctp_tsnmap_has_gap(map) && gap == 0) {
                /* In this case the map has no gaps and the tsn we are
                 * recording is the next expected tsn.  We don't touch
                 * the map but simply bump the values.
                 */
                map->max_tsn_seen++;
                map->cumulative_tsn_ack_point++;
                if (trans)
                        trans->sack_generation =
                                trans->asoc->peer.sack_generation;
                map->base_tsn++;
        } else {
                /* Either we already have a gap, or about to record a gap, so
                 * have work to do.
                 *
                 * Bump the max.
                 */
                if (TSN_lt(map->max_tsn_seen, tsn))
                        map->max_tsn_seen = tsn;

                /* Mark the TSN as received.  */
                set_bit(gap, map->tsn_map);

                /* Go fixup any internal TSN mapping variables including
                 * cumulative_tsn_ack_point.
                 */
                sctp_tsnmap_update(map);
        }

        return 0;
}


/* Initialize a Gap Ack Block iterator from memory being provided.  */
static void sctp_tsnmap_iter_init(const struct sctp_tsnmap *map,
                                  struct sctp_tsnmap_iter *iter)
{
        /* Only start looking one past the Cumulative TSN Ack Point.  */
        iter->start = map->cumulative_tsn_ack_point + 1;
}

/* Get the next Gap Ack Blocks. Returns 0 if there was not another block
 * to get.
 */
static int sctp_tsnmap_next_gap_ack(const struct sctp_tsnmap *map,
                                    struct sctp_tsnmap_iter *iter,
                                    __u16 *start, __u16 *end)
{
        int ended = 0;
        __u16 start_ = 0, end_ = 0, offset;

        /* If there are no more gap acks possible, get out fast.  */
        if (TSN_lte(map->max_tsn_seen, iter->start))
                return 0;

        offset = iter->start - map->base_tsn;
        sctp_tsnmap_find_gap_ack(map->tsn_map, offset, map->len,
                                 &start_, &end_);

        /* The Gap Ack Block happens to end at the end of the map. */
        if (start_ && !end_)
                end_ = map->len - 1;

        /* If we found a Gap Ack Block, return the start and end and
         * bump the iterator forward.
         */
        if (end_) {
                /* Fix up the start and end based on the
                 * Cumulative TSN Ack which is always 1 behind base.
                 */
                *start = start_ + 1;
                *end = end_ + 1;

                /* Move the iterator forward.  */
                iter->start = map->cumulative_tsn_ack_point + *end + 1;
                ended = 1;
        }

        return ended;
}

/* Mark this and any lower TSN as seen.  */
void sctp_tsnmap_skip(struct sctp_tsnmap *map, __u32 tsn)
{
        u32 gap;

        if (TSN_lt(tsn, map->base_tsn))
                return;
        if (!TSN_lt(tsn, map->base_tsn + SCTP_TSN_MAP_SIZE))
                return;

        /* Bump the max.  */
        if (TSN_lt(map->max_tsn_seen, tsn))
                map->max_tsn_seen = tsn;

        gap = tsn - map->base_tsn + 1;

        map->base_tsn += gap;
        map->cumulative_tsn_ack_point += gap;
        if (gap >= map->len) {
                /* If our gap is larger then the map size, just
                 * zero out the map.
                 */
                bitmap_zero(map->tsn_map, map->len);
        } else {
                /* If the gap is smaller than the map size,
                 * shift the map by 'gap' bits and update further.
                 */
                bitmap_shift_right(map->tsn_map, map->tsn_map, gap, map->len);
                sctp_tsnmap_update(map);
        }
}

/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* This private helper function updates the tsnmap buffers and
 * the Cumulative TSN Ack Point.
 */
static void sctp_tsnmap_update(struct sctp_tsnmap *map)
{
        u16 len;
        unsigned long zero_bit;


        len = map->max_tsn_seen - map->cumulative_tsn_ack_point;
        zero_bit = find_first_zero_bit(map->tsn_map, len);
        if (!zero_bit)
                return;         /* The first 0-bit is bit 0.  nothing to do */

        map->base_tsn += zero_bit;
        map->cumulative_tsn_ack_point += zero_bit;

        bitmap_shift_right(map->tsn_map, map->tsn_map, zero_bit, map->len);
}

/* How many data chunks  are we missing from our peer?
 */
__u16 sctp_tsnmap_pending(struct sctp_tsnmap *map)
{
        __u32 cum_tsn = map->cumulative_tsn_ack_point;
        __u32 max_tsn = map->max_tsn_seen;
        __u32 base_tsn = map->base_tsn;
        __u16 pending_data;
        u32 gap;

        pending_data = max_tsn - cum_tsn;
        gap = max_tsn - base_tsn;

        if (gap == 0 || gap >= map->len)
                goto out;

        pending_data -= bitmap_weight(map->tsn_map, gap + 1);
out:
        return pending_data;
}

/* This is a private helper for finding Gap Ack Blocks.  It searches a
 * single array for the start and end of a Gap Ack Block.
 *
 * The flags "started" and "ended" tell is if we found the beginning
 * or (respectively) the end of a Gap Ack Block.
 */
static void sctp_tsnmap_find_gap_ack(unsigned long *map, __u16 off,
                                     __u16 len, __u16 *start, __u16 *end)
{
        int i = off;

        /* Look through the entire array, but break out
         * early if we have found the end of the Gap Ack Block.
         */

        /* Also, stop looking past the maximum TSN seen. */

        /* Look for the start. */
        i = find_next_bit(map, len, off);
        if (i < len)
                *start = i;

        /* Look for the end.  */
        if (*start) {
                /* We have found the start, let's find the
                 * end.  If we find the end, break out.
                 */
                i = find_next_zero_bit(map, len, i);
                if (i < len)
                        *end = i - 1;
        }
}

/* Renege that we have seen a TSN.  */
void sctp_tsnmap_renege(struct sctp_tsnmap *map, __u32 tsn)
{
        u32 gap;

        if (TSN_lt(tsn, map->base_tsn))
                return;
        /* Assert: TSN is in range.  */
        if (!TSN_lt(tsn, map->base_tsn + map->len))
                return;

        gap = tsn - map->base_tsn;

        /* Pretend we never saw the TSN.  */
        clear_bit(gap, map->tsn_map);
}

/* How many gap ack blocks do we have recorded? */
__u16 sctp_tsnmap_num_gabs(struct sctp_tsnmap *map,
                           struct sctp_gap_ack_block *gabs)
{
        struct sctp_tsnmap_iter iter;
        int ngaps = 0;

        /* Refresh the gap ack information. */
        if (sctp_tsnmap_has_gap(map)) {
                __u16 start = 0, end = 0;
                sctp_tsnmap_iter_init(map, &iter);
                while (sctp_tsnmap_next_gap_ack(map, &iter,
                                                &start,
                                                &end)) {

                        gabs[ngaps].start = htons(start);
                        gabs[ngaps].end = htons(end);
                        ngaps++;
                        if (ngaps >= SCTP_MAX_GABS)
                                break;
                }
        }
        return ngaps;
}

static int sctp_tsnmap_grow(struct sctp_tsnmap *map, u16 size)
{
        unsigned long *new;
        unsigned long inc;
        u16  len;

        if (size > SCTP_TSN_MAP_SIZE)
                return 0;

        inc = ALIGN((size - map->len), BITS_PER_LONG) + SCTP_TSN_MAP_INCREMENT;
        len = min_t(u16, map->len + inc, SCTP_TSN_MAP_SIZE);

        new = kzalloc(len>>3, GFP_ATOMIC);
        if (!new)
                return 0;

        bitmap_copy(new, map->tsn_map,
                map->max_tsn_seen - map->cumulative_tsn_ack_point);
        kfree(map->tsn_map);
        map->tsn_map = new;
        map->len = len;

        return 1;
}