net/dccp/ackvec.c

   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
  13 #include "ackvec.h"
  14 #include "dccp.h"
  15
  16 #include <linux/init.h>
  17 #include <linux/errno.h>
  18 #include <linux/kernel.h>
  19 #include <linux/skbuff.h>
  20 #include <linux/slab.h>
  21
  22 #include <net/sock.h>
  23
  24 static struct kmem_cache *dccp_ackvec_slab;
  25 static struct kmem_cache *dccp_ackvec_record_slab;
  26
  27 struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
  28 {
  29         struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
  30
  31         if (av != NULL) {
  32                 av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
  33                 INIT_LIST_HEAD(&av->av_records);
  34         }
  35         return av;
  36 }
  37
  38 static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
  39 {
  40         struct dccp_ackvec_record *cur, *next;
  41
  42         list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
  43                 kmem_cache_free(dccp_ackvec_record_slab, cur);
  44         INIT_LIST_HEAD(&av->av_records);
  45 }
  46
  47 void dccp_ackvec_free(struct dccp_ackvec *av)
  48 {
  49         if (likely(av != NULL)) {
  50                 dccp_ackvec_purge_records(av);
  51                 kmem_cache_free(dccp_ackvec_slab, av);
  52         }
  53 }
  54
  55 /**
  56  * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
  57  * @av:         Ack Vector records to update
  58  * @seqno:      Sequence number of the packet carrying the Ack Vector just sent
  59  * @nonce_sum:  The sum of all buffer nonces contained in the Ack Vector
  60  */
  61 int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
  62 {
  63         struct dccp_ackvec_record *avr;
  64
  65         avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
  66         if (avr == NULL)
  67                 return -ENOBUFS;
  68
  69         avr->avr_ack_seqno  = seqno;
  70         avr->avr_ack_ptr    = av->av_buf_head;
  71         avr->avr_ack_ackno  = av->av_buf_ackno;
  72         avr->avr_ack_nonce  = nonce_sum;
  73         avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
  74         /*
  75          * When the buffer overflows, we keep no more than one record. This is
  76          * the simplest way of disambiguating sender-Acks dating from before the
  77          * overflow from sender-Acks which refer to after the overflow; a simple
  78          * solution is preferable here since we are handling an exception.
  79          */
  80         if (av->av_overflow)
  81                 dccp_ackvec_purge_records(av);
  82         /*
  83          * Since GSS is incremented for each packet, the list is automatically
  84          * arranged in descending order of @ack_seqno.
  85          */
  86         list_add(&avr->avr_node, &av->av_records);
  87
  88         dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
  89                       (unsigned long long)avr->avr_ack_seqno,
  90                       (unsigned long long)avr->avr_ack_ackno,
  91                       avr->avr_ack_runlen);
  92         return 0;
  93 }
  94
  95 static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
  96                                                      const u64 ackno)
  97 {
  98         struct dccp_ackvec_record *avr;
  99         /*
 100          * Exploit that records are inserted in descending order of sequence
 101          * number, start with the oldest record first. If @ackno is `before'
 102          * the earliest ack_ackno, the packet is too old to be considered.
 103          */
 104         list_for_each_entry_reverse(avr, av_list, avr_node) {
 105                 if (avr->avr_ack_seqno == ackno)
 106                         return avr;
 107                 if (before48(ackno, avr->avr_ack_seqno))
 108                         break;
 109         }
 110         return NULL;
 111 }
 112
 113 /*
 114  * Buffer index and length computation using modulo-buffersize arithmetic.
 115  * Note that, as pointers move from right to left, head is `before' tail.
 116  */
 117 static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
 118 {
 119         return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
 120 }
 121
 122 static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
 123 {
 124         return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
 125 }
 126
 127 u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
 128 {
 129         if (unlikely(av->av_overflow))
 130                 return DCCPAV_MAX_ACKVEC_LEN;
 131         return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
 132 }
 133
 134 /*
 135  * If several packets are missing, the HC-Receiver may prefer to enter multiple
 136  * bytes with run length 0, rather than a single byte with a larger run length;
 137  * this simplifies table updates if one of the missing packets arrives.
 138  */
 139 static inline int dccp_ackvec_set_buf_head_state(struct dccp_ackvec *av,
 140                                                  const unsigned int packets,
 141                                                  const unsigned char state)
 142 {
 143         long gap;
 144         long new_head;
 145
 146         if (av->av_vec_len + packets > DCCPAV_MAX_ACKVEC_LEN)
 147                 return -ENOBUFS;
 148
 149         gap      = packets - 1;
 150         new_head = av->av_buf_head - packets;
 151
 152         if (new_head < 0) {
 153                 if (gap > 0) {
 154                         memset(av->av_buf, DCCPAV_NOT_RECEIVED,
 155                                gap + new_head + 1);
 156                         gap = -new_head;
 157                 }
 158                 new_head += DCCPAV_MAX_ACKVEC_LEN;
 159         }
 160
 161         av->av_buf_head = new_head;
 162
 163         if (gap > 0)
 164                 memset(av->av_buf + av->av_buf_head + 1,
 165                        DCCPAV_NOT_RECEIVED, gap);
 166
 167         av->av_buf[av->av_buf_head] = state;
 168         av->av_vec_len += packets;
 169         return 0;
 170 }
 171
 172 /*
 173  * Implements the RFC 4340, Appendix A
 174  */
 175 int dccp_ackvec_add(struct dccp_ackvec *av, const struct sock *sk,
 176                     const u64 ackno, const u8 state)
 177 {
 178         u8 *cur_head = av->av_buf + av->av_buf_head,
 179            *buf_end  = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;
 180         /*
 181          * Check at the right places if the buffer is full, if it is, tell the
 182          * caller to start dropping packets till the HC-Sender acks our ACK
 183          * vectors, when we will free up space in av_buf.
 184          *
 185          * We may well decide to do buffer compression, etc, but for now lets
 186          * just drop.
 187          *
 188          * From Appendix A.1.1 (`New Packets'):
 189          *
 190          *      Of course, the circular buffer may overflow, either when the
 191          *      HC-Sender is sending data at a very high rate, when the
 192          *      HC-Receiver's acknowledgements are not reaching the HC-Sender,
 193          *      or when the HC-Sender is forgetting to acknowledge those acks
 194          *      (so the HC-Receiver is unable to clean up old state). In this
 195          *      case, the HC-Receiver should either compress the buffer (by
 196          *      increasing run lengths when possible), transfer its state to
 197          *      a larger buffer, or, as a last resort, drop all received
 198          *      packets, without processing them whatsoever, until its buffer
 199          *      shrinks again.
 200          */
 201
 202         /* See if this is the first ackno being inserted */
 203         if (av->av_vec_len == 0) {
 204                 *cur_head = state;
 205                 av->av_vec_len = 1;
 206         } else if (after48(ackno, av->av_buf_ackno)) {
 207                 const u64 delta = dccp_delta_seqno(av->av_buf_ackno, ackno);
 208
 209                 /*
 210                  * Look if the state of this packet is the same as the
 211                  * previous ackno and if so if we can bump the head len.
 212                  */
 213                 if (delta == 1 && dccp_ackvec_state(cur_head) == state &&
 214                     dccp_ackvec_runlen(cur_head) < DCCPAV_MAX_RUNLEN)
 215                         *cur_head += 1;
 216                 else if (dccp_ackvec_set_buf_head_state(av, delta, state))
 217                         return -ENOBUFS;
 218         } else {
 219                 /*
 220                  * A.1.2.  Old Packets
 221                  *
 222                  *      When a packet with Sequence Number S <= buf_ackno
 223                  *      arrives, the HC-Receiver will scan the table for
 224                  *      the byte corresponding to S. (Indexing structures
 225                  *      could reduce the complexity of this scan.)
 226                  */
 227                 u64 delta = dccp_delta_seqno(ackno, av->av_buf_ackno);
 228
 229                 while (1) {
 230                         const u8 len = dccp_ackvec_runlen(cur_head);
 231                         /*
 232                          * valid packets not yet in av_buf have a reserved
 233                          * entry, with a len equal to 0.
 234                          */
 235                         if (*cur_head == DCCPAV_NOT_RECEIVED && delta == 0) {
 236                                 dccp_pr_debug("Found %llu reserved seat!\n",
 237                                               (unsigned long long)ackno);
 238                                 *cur_head = state;
 239                                 goto out;
 240                         }
 241                         /* len == 0 means one packet */
 242                         if (delta < len + 1)
 243                                 goto out_duplicate;
 244
 245                         delta -= len + 1;
 246                         if (++cur_head == buf_end)
 247                                 cur_head = av->av_buf;
 248                 }
 249         }
 250
 251         av->av_buf_ackno = ackno;
 252 out:
 253         return 0;
 254
 255 out_duplicate:
 256         /* Duplicate packet */
 257         dccp_pr_debug("Received a dup or already considered lost "
 258                       "packet: %llu\n", (unsigned long long)ackno);
 259         return -EILSEQ;
 260 }
 261
 262 static void dccp_ackvec_throw_record(struct dccp_ackvec *av,
 263                                      struct dccp_ackvec_record *avr)
 264 {
 265         struct dccp_ackvec_record *next;
 266
 267         /* sort out vector length */
 268         if (av->av_buf_head <= avr->avr_ack_ptr)
 269                 av->av_vec_len = avr->avr_ack_ptr - av->av_buf_head;
 270         else
 271                 av->av_vec_len = DCCPAV_MAX_ACKVEC_LEN - 1 -
 272                                  av->av_buf_head + avr->avr_ack_ptr;
 273
 274         /* free records */
 275         list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
 276                 list_del(&avr->avr_node);
 277                 kmem_cache_free(dccp_ackvec_record_slab, avr);
 278         }
 279 }
 280
 281 void dccp_ackvec_check_rcv_ackno(struct dccp_ackvec *av, struct sock *sk,
 282                                  const u64 ackno)
 283 {
 284         struct dccp_ackvec_record *avr;
 285
 286         /*
 287          * If we traverse backwards, it should be faster when we have large
 288          * windows. We will be receiving ACKs for stuff we sent a while back
 289          * -sorbo.
 290          */
 291         list_for_each_entry_reverse(avr, &av->av_records, avr_node) {
 292                 if (ackno == avr->avr_ack_seqno) {
 293                         dccp_pr_debug("%s ACK packet 0, len=%d, ack_seqno=%llu, "
 294                                       "ack_ackno=%llu, ACKED!\n",
 295                                       dccp_role(sk), avr->avr_ack_runlen,
 296                                       (unsigned long long)avr->avr_ack_seqno,
 297                                       (unsigned long long)avr->avr_ack_ackno);
 298                         dccp_ackvec_throw_record(av, avr);
 299                         break;
 300                 } else if (avr->avr_ack_seqno > ackno)
 301                         break; /* old news */
 302         }
 303 }
 304
 305 static void dccp_ackvec_check_rcv_ackvector(struct dccp_ackvec *av,
 306                                             struct sock *sk, u64 *ackno,
 307                                             const unsigned char len,
 308                                             const unsigned char *vector)
 309 {
 310         unsigned char i;
 311         struct dccp_ackvec_record *avr;
 312
 313         /* Check if we actually sent an ACK vector */
 314         if (list_empty(&av->av_records))
 315                 return;
 316
 317         i = len;
 318         /*
 319          * XXX
 320          * I think it might be more efficient to work backwards. See comment on
 321          * rcv_ackno. -sorbo.
 322          */
 323         avr = list_entry(av->av_records.next, struct dccp_ackvec_record, avr_node);
 324         while (i--) {
 325                 const u8 rl = dccp_ackvec_runlen(vector);
 326                 u64 ackno_end_rl;
 327
 328                 dccp_set_seqno(&ackno_end_rl, *ackno - rl);
 329
 330                 /*
 331                  * If our AVR sequence number is greater than the ack, go
 332                  * forward in the AVR list until it is not so.
 333                  */
 334                 list_for_each_entry_from(avr, &av->av_records, avr_node) {
 335                         if (!after48(avr->avr_ack_seqno, *ackno))
 336                                 goto found;
 337                 }
 338                 /* End of the av_records list, not found, exit */
 339                 break;
 340 found:
 341                 if (between48(avr->avr_ack_seqno, ackno_end_rl, *ackno)) {
 342                         if (dccp_ackvec_state(vector) != DCCPAV_NOT_RECEIVED) {
 343                                 dccp_pr_debug("%s ACK vector 0, len=%d, "
 344                                               "ack_seqno=%llu, ack_ackno=%llu, "
 345                                               "ACKED!\n",
 346                                               dccp_role(sk), len,
 347                                               (unsigned long long)
 348                                               avr->avr_ack_seqno,
 349                                               (unsigned long long)
 350                                               avr->avr_ack_ackno);
 351                                 dccp_ackvec_throw_record(av, avr);
 352                                 break;
 353                         }
 354                         /*
 355                          * If it wasn't received, continue scanning... we might
 356                          * find another one.
 357                          */
 358                 }
 359
 360                 dccp_set_seqno(ackno, ackno_end_rl - 1);
 361                 ++vector;
 362         }
 363 }
 364
 365 int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb,
 366                       u64 *ackno, const u8 opt, const u8 *value, const u8 len)
 367 {
 368         if (len > DCCP_SINGLE_OPT_MAXLEN)
 369                 return -1;
 370
 371         /* dccp_ackvector_print(DCCP_SKB_CB(skb)->dccpd_ack_seq, value, len); */
 372         dccp_ackvec_check_rcv_ackvector(dccp_sk(sk)->dccps_hc_rx_ackvec, sk,
 373                                         ackno, len, value);
 374         return 0;
 375 }
 376
 377 /**
 378  * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
 379  * This routine is called when the peer acknowledges the receipt of Ack Vectors
 380  * up to and including @ackno. While based on on section A.3 of RFC 4340, here
 381  * are additional precautions to prevent corrupted buffer state. In particular,
 382  * we use tail_ackno to identify outdated records; it always marks the earliest
 383  * packet of group (2) in 11.4.2.
 384  */
 385 void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
 386  {
 387         struct dccp_ackvec_record *avr, *next;
 388         u8 runlen_now, eff_runlen;
 389         s64 delta;
 390
 391         avr = dccp_ackvec_lookup(&av->av_records, ackno);
 392         if (avr == NULL)
 393                 return;
 394         /*
 395          * Deal with outdated acknowledgments: this arises when e.g. there are
 396          * several old records and the acks from the peer come in slowly. In
 397          * that case we may still have records that pre-date tail_ackno.
 398          */
 399         delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
 400         if (delta < 0)
 401                 goto free_records;
 402         /*
 403          * Deal with overlapping Ack Vectors: don't subtract more than the
 404          * number of packets between tail_ackno and ack_ackno.
 405          */
 406         eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
 407
 408         runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
 409         /*
 410          * The run length of Ack Vector cells does not decrease over time. If
 411          * the run length is the same as at the time the Ack Vector was sent, we
 412          * free the ack_ptr cell. That cell can however not be freed if the run
 413          * length has increased: in this case we need to move the tail pointer
 414          * backwards (towards higher indices), to its next-oldest neighbour.
 415          */
 416         if (runlen_now > eff_runlen) {
 417
 418                 av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
 419                 av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
 420
 421                 /* This move may not have cleared the overflow flag. */
 422                 if (av->av_overflow)
 423                         av->av_overflow = (av->av_buf_head == av->av_buf_tail);
 424         } else {
 425                 av->av_buf_tail = avr->avr_ack_ptr;
 426                 /*
 427                  * We have made sure that avr points to a valid cell within the
 428                  * buffer. This cell is either older than head, or equals head
 429                  * (empty buffer): in both cases we no longer have any overflow.
 430                  */
 431                 av->av_overflow = 0;
 432         }
 433
 434         /*
 435          * The peer has acknowledged up to and including ack_ackno. Hence the
 436          * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
 437          */
 438         av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
 439
 440 free_records:
 441         list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
 442                 list_del(&avr->avr_node);
 443                 kmem_cache_free(dccp_ackvec_record_slab, avr);
 444         }
 445 }
 446
 447 int __init dccp_ackvec_init(void)
 448 {
 449         dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
 450                                              sizeof(struct dccp_ackvec), 0,
 451                                              SLAB_HWCACHE_ALIGN, NULL);
 452         if (dccp_ackvec_slab == NULL)
 453                 goto out_err;
 454
 455         dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
 456                                              sizeof(struct dccp_ackvec_record),
 457                                              0, SLAB_HWCACHE_ALIGN, NULL);
 458         if (dccp_ackvec_record_slab == NULL)
 459                 goto out_destroy_slab;
 460
 461         return 0;
 462
 463 out_destroy_slab:
 464         kmem_cache_destroy(dccp_ackvec_slab);
 465         dccp_ackvec_slab = NULL;
 466 out_err:
 467         DCCP_CRIT("Unable to create Ack Vector slab cache");
 468         return -ENOBUFS;
 469 }
 470
 471 void dccp_ackvec_exit(void)
 472 {
 473         if (dccp_ackvec_slab != NULL) {
 474                 kmem_cache_destroy(dccp_ackvec_slab);
 475                 dccp_ackvec_slab = NULL;
 476         }
 477         if (dccp_ackvec_record_slab != NULL) {
 478                 kmem_cache_destroy(dccp_ackvec_record_slab);
 479                 dccp_ackvec_record_slab = NULL;
 480         }
 481 }