packet_history.c

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/*
 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
 *
 *  An implementation of the DCCP protocol
 *
 *  This code has been developed by the University of Waikato WAND
 *  research group. For further information please see http://www.wand.net.nz/
 *  or e-mail Ian McDonald - [email protected]
 *
 *  This code also uses code from Lulea University, rereleased as GPL by its
 *  authors:
 *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
 *
 *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
 *  and to make it work as a loadable module in the DCCP stack written by
 *  Arnaldo Carvalho de Melo <[email protected]>.
 *
 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <[email protected]>
 *
 *  This program 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.
 *
 *  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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/string.h>
#include <linux/slab.h>
#include "packet_history.h"
#include "../../dccp.h"

/*
 * Transmitter History Routines
 */
static struct kmem_cache *tfrc_tx_hist_slab;

int __init tfrc_tx_packet_history_init(void)
{
    tfrc_tx_hist_slab = kmem_cache_create("tfrc_tx_hist",
                          sizeof(struct tfrc_tx_hist_entry),
                          0, SLAB_HWCACHE_ALIGN, NULL);
    return tfrc_tx_hist_slab == NULL ? -ENOBUFS : 0;
}

void tfrc_tx_packet_history_exit(void)
{
    if (tfrc_tx_hist_slab != NULL) {
        kmem_cache_destroy(tfrc_tx_hist_slab);
        tfrc_tx_hist_slab = NULL;
    }
}

int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
{
    struct tfrc_tx_hist_entry *entry = kmem_cache_alloc(tfrc_tx_hist_slab, gfp_any());

    if (entry == NULL)
        return -ENOBUFS;
    entry->seqno = seqno;
    entry->stamp = ktime_get_real();
    entry->next  = *headp;
    *headp       = entry;
    return 0;
}

void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
{
    struct tfrc_tx_hist_entry *head = *headp;

    while (head != NULL) {
        struct tfrc_tx_hist_entry *next = head->next;

        kmem_cache_free(tfrc_tx_hist_slab, head);
        head = next;
    }

    *headp = NULL;
}

/*
 *  Receiver History Routines
 */
static struct kmem_cache *tfrc_rx_hist_slab;

int __init tfrc_rx_packet_history_init(void)
{
    tfrc_rx_hist_slab = kmem_cache_create("tfrc_rxh_cache",
                          sizeof(struct tfrc_rx_hist_entry),
                          0, SLAB_HWCACHE_ALIGN, NULL);
    return tfrc_rx_hist_slab == NULL ? -ENOBUFS : 0;
}

void tfrc_rx_packet_history_exit(void)
{
    if (tfrc_rx_hist_slab != NULL) {
        kmem_cache_destroy(tfrc_rx_hist_slab);
        tfrc_rx_hist_slab = NULL;
    }
}

static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,
                           const struct sk_buff *skb,
                           const u64 ndp)
{
    const struct dccp_hdr *dh = dccp_hdr(skb);

    entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
    entry->tfrchrx_ccval = dh->dccph_ccval;
    entry->tfrchrx_type  = dh->dccph_type;
    entry->tfrchrx_ndp   = ndp;
    entry->tfrchrx_tstamp = ktime_get_real();
}

void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
                 const struct sk_buff *skb,
                 const u64 ndp)
{
    struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);

    tfrc_rx_hist_entry_from_skb(entry, skb, ndp);
}

/* has the packet contained in skb been seen before? */
int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb)
{
    const u64 seq = DCCP_SKB_CB(skb)->dccpd_seq;
    int i;

    if (dccp_delta_seqno(tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno, seq) <= 0)
        return 1;

    for (i = 1; i <= h->loss_count; i++)
        if (tfrc_rx_hist_entry(h, i)->tfrchrx_seqno == seq)
            return 1;

    return 0;
}

static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)
{
    const u8 idx_a = tfrc_rx_hist_index(h, a),
         idx_b = tfrc_rx_hist_index(h, b);
    struct tfrc_rx_hist_entry *tmp = h->ring[idx_a];

    h->ring[idx_a] = h->ring[idx_b];
    h->ring[idx_b] = tmp;
}

/*
 * Private helper functions for loss detection.
 *
 * In the descriptions, `Si' refers to the sequence number of entry number i,
 * whose NDP count is `Ni' (lower case is used for variables).
 * Note: All __xxx_loss functions expect that a test against duplicates has been
 *       performed already: the seqno of the skb must not be less than the seqno
 *       of loss_prev; and it must not equal that of any valid history entry.
 */
static void __do_track_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u64 n1)
{
    u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
        s1 = DCCP_SKB_CB(skb)->dccpd_seq;

    if (!dccp_loss_free(s0, s1, n1)) {  /* gap between S0 and S1 */
        h->loss_count = 1;
        tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n1);
    }
}

static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2)
{
    u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
        s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
        s2 = DCCP_SKB_CB(skb)->dccpd_seq;

    if (likely(dccp_delta_seqno(s1, s2) > 0)) { /* S1  <  S2 */
        h->loss_count = 2;
        tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
        return;
    }

    /* S0  <  S2  <  S1 */

    if (dccp_loss_free(s0, s2, n2)) {
        u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;

        if (dccp_loss_free(s2, s1, n1)) {
            /* hole is filled: S0, S2, and S1 are consecutive */
            h->loss_count = 0;
            h->loss_start = tfrc_rx_hist_index(h, 1);
        } else
            /* gap between S2 and S1: just update loss_prev */
            tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);

    } else {    /* gap between S0 and S2 */
        /*
         * Reorder history to insert S2 between S0 and S1
         */
        tfrc_rx_hist_swap(h, 0, 3);
        h->loss_start = tfrc_rx_hist_index(h, 3);
        tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n2);
        h->loss_count = 2;
    }
}

/* return 1 if a new loss event has been identified */
static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
{
    u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
        s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
        s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
        s3 = DCCP_SKB_CB(skb)->dccpd_seq;

    if (likely(dccp_delta_seqno(s2, s3) > 0)) { /* S2  <  S3 */
        h->loss_count = 3;
        tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
        return 1;
    }

    /* S3  <  S2 */

    if (dccp_delta_seqno(s1, s3) > 0) {     /* S1  <  S3  <  S2 */
        /*
         * Reorder history to insert S3 between S1 and S2
         */
        tfrc_rx_hist_swap(h, 2, 3);
        tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
        h->loss_count = 3;
        return 1;
    }

    /* S0  <  S3  <  S1 */

    if (dccp_loss_free(s0, s3, n3)) {
        u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;

        if (dccp_loss_free(s3, s1, n1)) {
            /* hole between S0 and S1 filled by S3 */
            u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;

            if (dccp_loss_free(s1, s2, n2)) {
                /* entire hole filled by S0, S3, S1, S2 */
                h->loss_start = tfrc_rx_hist_index(h, 2);
                h->loss_count = 0;
            } else {
                /* gap remains between S1 and S2 */
                h->loss_start = tfrc_rx_hist_index(h, 1);
                h->loss_count = 1;
            }

        } else /* gap exists between S3 and S1, loss_count stays at 2 */
            tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n3);

        return 0;
    }

    /*
     * The remaining case:  S0  <  S3  <  S1  <  S2;  gap between S0 and S3
     * Reorder history to insert S3 between S0 and S1.
     */
    tfrc_rx_hist_swap(h, 0, 3);
    h->loss_start = tfrc_rx_hist_index(h, 3);
    tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n3);
    h->loss_count = 3;

    return 1;
}

/* recycle RX history records to continue loss detection if necessary */
static void __three_after_loss(struct tfrc_rx_hist *h)
{
    /*
     * At this stage we know already that there is a gap between S0 and S1
     * (since S0 was the highest sequence number received before detecting
     * the loss). To recycle the loss record, it is thus only necessary to
     * check for other possible gaps between S1/S2 and between S2/S3.
     */
    u64 s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
        s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
        s3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_seqno;
    u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
        n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;

    if (dccp_loss_free(s1, s2, n2)) {

        if (dccp_loss_free(s2, s3, n3)) {
            /* no gap between S2 and S3: entire hole is filled */
            h->loss_start = tfrc_rx_hist_index(h, 3);
            h->loss_count = 0;
        } else {
            /* gap between S2 and S3 */
            h->loss_start = tfrc_rx_hist_index(h, 2);
            h->loss_count = 1;
        }

    } else {    /* gap between S1 and S2 */
        h->loss_start = tfrc_rx_hist_index(h, 1);
        h->loss_count = 2;
    }
}

int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
            struct tfrc_loss_hist *lh,
            struct sk_buff *skb, const u64 ndp,
            u32 (*calc_first_li)(struct sock *), struct sock *sk)
{
    int is_new_loss = 0;

    if (h->loss_count == 0) {
        __do_track_loss(h, skb, ndp);
    } else if (h->loss_count == 1) {
        __one_after_loss(h, skb, ndp);
    } else if (h->loss_count != 2) {
        DCCP_BUG("invalid loss_count %d", h->loss_count);
    } else if (__two_after_loss(h, skb, ndp)) {
        /*
         * Update Loss Interval database and recycle RX records
         */
        is_new_loss = tfrc_lh_interval_add(lh, h, calc_first_li, sk);
        __three_after_loss(h);
    }
    return is_new_loss;
}

int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
{
    int i;

    for (i = 0; i <= TFRC_NDUPACK; i++) {
        h->ring[i] = kmem_cache_alloc(tfrc_rx_hist_slab, GFP_ATOMIC);
        if (h->ring[i] == NULL)
            goto out_free;
    }

    h->loss_count = h->loss_start = 0;
    return 0;

out_free:
    while (i-- != 0) {
        kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
        h->ring[i] = NULL;
    }
    return -ENOBUFS;
}

void tfrc_rx_hist_purge(struct tfrc_rx_hist *h)
{
    int i;

    for (i = 0; i <= TFRC_NDUPACK; ++i)
        if (h->ring[i] != NULL) {
            kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
            h->ring[i] = NULL;
        }
}

static inline struct tfrc_rx_hist_entry *
            tfrc_rx_hist_rtt_last_s(const struct tfrc_rx_hist *h)
{
    return h->ring[0];
}

static inline struct tfrc_rx_hist_entry *
            tfrc_rx_hist_rtt_prev_s(const struct tfrc_rx_hist *h)
{
    return h->ring[h->rtt_sample_prev];
}

u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)
{
    u32 sample = 0,
        delta_v = SUB16(dccp_hdr(skb)->dccph_ccval,
                tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);

    if (delta_v < 1 || delta_v > 4) {   /* unsuitable CCVal delta */
        if (h->rtt_sample_prev == 2) {  /* previous candidate stored */
            sample = SUB16(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
                       tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
            if (sample)
                sample = 4 / sample *
                         ktime_us_delta(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_tstamp,
                            tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp);
            else    /*
                 * FIXME: This condition is in principle not
                 * possible but occurs when CCID is used for
                 * two-way data traffic. I have tried to trace
                 * it, but the cause does not seem to be here.
                 */
                DCCP_BUG("please report to [email protected]"
                     " => prev = %u, last = %u",
                     tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
                     tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
        } else if (delta_v < 1) {
            h->rtt_sample_prev = 1;
            goto keep_ref_for_next_time;
        }

    } else if (delta_v == 4) /* optimal match */
        sample = ktime_to_us(net_timedelta(tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp));
    else {           /* suboptimal match */
        h->rtt_sample_prev = 2;
        goto keep_ref_for_next_time;
    }

    if (unlikely(sample > DCCP_SANE_RTT_MAX)) {
        DCCP_WARN("RTT sample %u too large, using max\n", sample);
        sample = DCCP_SANE_RTT_MAX;
    }

    h->rtt_sample_prev = 0;        /* use current entry as next reference */
keep_ref_for_next_time:

    return sample;
}