linux/net/dccp/ackvec.c
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   1/*
   2 *  net/dccp/ackvec.c
   3 *
   4 *  An implementation of Ack Vectors for the DCCP protocol
   5 *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
   6 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
   7 *
   8 *      This program is free software; you can redistribute it and/or modify it
   9 *      under the terms of the GNU General Public License as published by the
  10 *      Free Software Foundation; version 2 of the License;
  11 */
  12#include "dccp.h"
  13#include <linux/kernel.h>
  14#include <linux/slab.h>
  15#include <linux/export.h>
  16
  17static struct kmem_cache *dccp_ackvec_slab;
  18static struct kmem_cache *dccp_ackvec_record_slab;
  19
  20struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
  21{
  22        struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
  23
  24        if (av != NULL) {
  25                av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
  26                INIT_LIST_HEAD(&av->av_records);
  27        }
  28        return av;
  29}
  30
  31static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
  32{
  33        struct dccp_ackvec_record *cur, *next;
  34
  35        list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
  36                kmem_cache_free(dccp_ackvec_record_slab, cur);
  37        INIT_LIST_HEAD(&av->av_records);
  38}
  39
  40void dccp_ackvec_free(struct dccp_ackvec *av)
  41{
  42        if (likely(av != NULL)) {
  43                dccp_ackvec_purge_records(av);
  44                kmem_cache_free(dccp_ackvec_slab, av);
  45        }
  46}
  47
  48/**
  49 * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
  50 * @av:         Ack Vector records to update
  51 * @seqno:      Sequence number of the packet carrying the Ack Vector just sent
  52 * @nonce_sum:  The sum of all buffer nonces contained in the Ack Vector
  53 */
  54int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
  55{
  56        struct dccp_ackvec_record *avr;
  57
  58        avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
  59        if (avr == NULL)
  60                return -ENOBUFS;
  61
  62        avr->avr_ack_seqno  = seqno;
  63        avr->avr_ack_ptr    = av->av_buf_head;
  64        avr->avr_ack_ackno  = av->av_buf_ackno;
  65        avr->avr_ack_nonce  = nonce_sum;
  66        avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
  67        /*
  68         * When the buffer overflows, we keep no more than one record. This is
  69         * the simplest way of disambiguating sender-Acks dating from before the
  70         * overflow from sender-Acks which refer to after the overflow; a simple
  71         * solution is preferable here since we are handling an exception.
  72         */
  73        if (av->av_overflow)
  74                dccp_ackvec_purge_records(av);
  75        /*
  76         * Since GSS is incremented for each packet, the list is automatically
  77         * arranged in descending order of @ack_seqno.
  78         */
  79        list_add(&avr->avr_node, &av->av_records);
  80
  81        dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
  82                      (unsigned long long)avr->avr_ack_seqno,
  83                      (unsigned long long)avr->avr_ack_ackno,
  84                      avr->avr_ack_runlen);
  85        return 0;
  86}
  87
  88static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
  89                                                     const u64 ackno)
  90{
  91        struct dccp_ackvec_record *avr;
  92        /*
  93         * Exploit that records are inserted in descending order of sequence
  94         * number, start with the oldest record first. If @ackno is `before'
  95         * the earliest ack_ackno, the packet is too old to be considered.
  96         */
  97        list_for_each_entry_reverse(avr, av_list, avr_node) {
  98                if (avr->avr_ack_seqno == ackno)
  99                        return avr;
 100                if (before48(ackno, avr->avr_ack_seqno))
 101                        break;
 102        }
 103        return NULL;
 104}
 105
 106/*
 107 * Buffer index and length computation using modulo-buffersize arithmetic.
 108 * Note that, as pointers move from right to left, head is `before' tail.
 109 */
 110static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
 111{
 112        return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
 113}
 114
 115static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
 116{
 117        return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
 118}
 119
 120u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
 121{
 122        if (unlikely(av->av_overflow))
 123                return DCCPAV_MAX_ACKVEC_LEN;
 124        return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
 125}
 126
 127/**
 128 * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
 129 * @av:         non-empty buffer to update
 130 * @distance:   negative or zero distance of @seqno from buf_ackno downward
 131 * @seqno:      the (old) sequence number whose record is to be updated
 132 * @state:      state in which packet carrying @seqno was received
 133 */
 134static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
 135                                   u64 seqno, enum dccp_ackvec_states state)
 136{
 137        u16 ptr = av->av_buf_head;
 138
 139        BUG_ON(distance > 0);
 140        if (unlikely(dccp_ackvec_is_empty(av)))
 141                return;
 142
 143        do {
 144                u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
 145
 146                if (distance + runlen >= 0) {
 147                        /*
 148                         * Only update the state if packet has not been received
 149                         * yet. This is OK as per the second table in RFC 4340,
 150                         * 11.4.1; i.e. here we are using the following table:
 151                         *                     RECEIVED
 152                         *                      0   1   3
 153                         *              S     +---+---+---+
 154                         *              T   0 | 0 | 0 | 0 |
 155                         *              O     +---+---+---+
 156                         *              R   1 | 1 | 1 | 1 |
 157                         *              E     +---+---+---+
 158                         *              D   3 | 0 | 1 | 3 |
 159                         *                    +---+---+---+
 160                         * The "Not Received" state was set by reserve_seats().
 161                         */
 162                        if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
 163                                av->av_buf[ptr] = state;
 164                        else
 165                                dccp_pr_debug("Not changing %llu state to %u\n",
 166                                              (unsigned long long)seqno, state);
 167                        break;
 168                }
 169
 170                distance += runlen + 1;
 171                ptr       = __ackvec_idx_add(ptr, 1);
 172
 173        } while (ptr != av->av_buf_tail);
 174}
 175
 176/* Mark @num entries after buf_head as "Not yet received". */
 177static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
 178{
 179        u16 start = __ackvec_idx_add(av->av_buf_head, 1),
 180            len   = DCCPAV_MAX_ACKVEC_LEN - start;
 181
 182        /* check for buffer wrap-around */
 183        if (num > len) {
 184                memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
 185                start = 0;
 186                num  -= len;
 187        }
 188        if (num)
 189                memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
 190}
 191
 192/**
 193 * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
 194 * @av:          container of buffer to update (can be empty or non-empty)
 195 * @num_packets: number of packets to register (must be >= 1)
 196 * @seqno:       sequence number of the first packet in @num_packets
 197 * @state:       state in which packet carrying @seqno was received
 198 */
 199static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
 200                                u64 seqno, enum dccp_ackvec_states state)
 201{
 202        u32 num_cells = num_packets;
 203
 204        if (num_packets > DCCPAV_BURST_THRESH) {
 205                u32 lost_packets = num_packets - 1;
 206
 207                DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
 208                /*
 209                 * We received 1 packet and have a loss of size "num_packets-1"
 210                 * which we squeeze into num_cells-1 rather than reserving an
 211                 * entire byte for each lost packet.
 212                 * The reason is that the vector grows in O(burst_length); when
 213                 * it grows too large there will no room left for the payload.
 214                 * This is a trade-off: if a few packets out of the burst show
 215                 * up later, their state will not be changed; it is simply too
 216                 * costly to reshuffle/reallocate/copy the buffer each time.
 217                 * Should such problems persist, we will need to switch to a
 218                 * different underlying data structure.
 219                 */
 220                for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
 221                        u8 len = min(lost_packets, (u32)DCCPAV_MAX_RUNLEN);
 222
 223                        av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
 224                        av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
 225
 226                        lost_packets -= len;
 227                }
 228        }
 229
 230        if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
 231                DCCP_CRIT("Ack Vector buffer overflow: dropping old entries\n");
 232                av->av_overflow = true;
 233        }
 234
 235        av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
 236        if (av->av_overflow)
 237                av->av_buf_tail = av->av_buf_head;
 238
 239        av->av_buf[av->av_buf_head] = state;
 240        av->av_buf_ackno            = seqno;
 241
 242        if (num_packets > 1)
 243                dccp_ackvec_reserve_seats(av, num_packets - 1);
 244}
 245
 246/**
 247 * dccp_ackvec_input  -  Register incoming packet in the buffer
 248 */
 249void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
 250{
 251        u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
 252        enum dccp_ackvec_states state = DCCPAV_RECEIVED;
 253
 254        if (dccp_ackvec_is_empty(av)) {
 255                dccp_ackvec_add_new(av, 1, seqno, state);
 256                av->av_tail_ackno = seqno;
 257
 258        } else {
 259                s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
 260                u8 *current_head = av->av_buf + av->av_buf_head;
 261
 262                if (num_packets == 1 &&
 263                    dccp_ackvec_state(current_head) == state &&
 264                    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
 265
 266                        *current_head   += 1;
 267                        av->av_buf_ackno = seqno;
 268
 269                } else if (num_packets > 0) {
 270                        dccp_ackvec_add_new(av, num_packets, seqno, state);
 271                } else {
 272                        dccp_ackvec_update_old(av, num_packets, seqno, state);
 273                }
 274        }
 275}
 276
 277/**
 278 * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
 279 * This routine is called when the peer acknowledges the receipt of Ack Vectors
 280 * up to and including @ackno. While based on on section A.3 of RFC 4340, here
 281 * are additional precautions to prevent corrupted buffer state. In particular,
 282 * we use tail_ackno to identify outdated records; it always marks the earliest
 283 * packet of group (2) in 11.4.2.
 284 */
 285void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
 286{
 287        struct dccp_ackvec_record *avr, *next;
 288        u8 runlen_now, eff_runlen;
 289        s64 delta;
 290
 291        avr = dccp_ackvec_lookup(&av->av_records, ackno);
 292        if (avr == NULL)
 293                return;
 294        /*
 295         * Deal with outdated acknowledgments: this arises when e.g. there are
 296         * several old records and the acks from the peer come in slowly. In
 297         * that case we may still have records that pre-date tail_ackno.
 298         */
 299        delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
 300        if (delta < 0)
 301                goto free_records;
 302        /*
 303         * Deal with overlapping Ack Vectors: don't subtract more than the
 304         * number of packets between tail_ackno and ack_ackno.
 305         */
 306        eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
 307
 308        runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
 309        /*
 310         * The run length of Ack Vector cells does not decrease over time. If
 311         * the run length is the same as at the time the Ack Vector was sent, we
 312         * free the ack_ptr cell. That cell can however not be freed if the run
 313         * length has increased: in this case we need to move the tail pointer
 314         * backwards (towards higher indices), to its next-oldest neighbour.
 315         */
 316        if (runlen_now > eff_runlen) {
 317
 318                av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
 319                av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
 320
 321                /* This move may not have cleared the overflow flag. */
 322                if (av->av_overflow)
 323                        av->av_overflow = (av->av_buf_head == av->av_buf_tail);
 324        } else {
 325                av->av_buf_tail = avr->avr_ack_ptr;
 326                /*
 327                 * We have made sure that avr points to a valid cell within the
 328                 * buffer. This cell is either older than head, or equals head
 329                 * (empty buffer): in both cases we no longer have any overflow.
 330                 */
 331                av->av_overflow = 0;
 332        }
 333
 334        /*
 335         * The peer has acknowledged up to and including ack_ackno. Hence the
 336         * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
 337         */
 338        av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
 339
 340free_records:
 341        list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
 342                list_del(&avr->avr_node);
 343                kmem_cache_free(dccp_ackvec_record_slab, avr);
 344        }
 345}
 346
 347/*
 348 *      Routines to keep track of Ack Vectors received in an skb
 349 */
 350int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
 351{
 352        struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
 353
 354        if (new == NULL)
 355                return -ENOBUFS;
 356        new->vec   = vec;
 357        new->len   = len;
 358        new->nonce = nonce;
 359
 360        list_add_tail(&new->node, head);
 361        return 0;
 362}
 363EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
 364
 365void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
 366{
 367        struct dccp_ackvec_parsed *cur, *next;
 368
 369        list_for_each_entry_safe(cur, next, parsed_chunks, node)
 370                kfree(cur);
 371        INIT_LIST_HEAD(parsed_chunks);
 372}
 373EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
 374
 375int __init dccp_ackvec_init(void)
 376{
 377        dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
 378                                             sizeof(struct dccp_ackvec), 0,
 379                                             SLAB_HWCACHE_ALIGN, NULL);
 380        if (dccp_ackvec_slab == NULL)
 381                goto out_err;
 382
 383        dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
 384                                             sizeof(struct dccp_ackvec_record),
 385                                             0, SLAB_HWCACHE_ALIGN, NULL);
 386        if (dccp_ackvec_record_slab == NULL)
 387                goto out_destroy_slab;
 388
 389        return 0;
 390
 391out_destroy_slab:
 392        kmem_cache_destroy(dccp_ackvec_slab);
 393        dccp_ackvec_slab = NULL;
 394out_err:
 395        DCCP_CRIT("Unable to create Ack Vector slab cache");
 396        return -ENOBUFS;
 397}
 398
 399void dccp_ackvec_exit(void)
 400{
 401        if (dccp_ackvec_slab != NULL) {
 402                kmem_cache_destroy(dccp_ackvec_slab);
 403                dccp_ackvec_slab = NULL;
 404        }
 405        if (dccp_ackvec_record_slab != NULL) {
 406                kmem_cache_destroy(dccp_ackvec_record_slab);
 407                dccp_ackvec_record_slab = NULL;
 408        }
 409}
 410
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