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 #include "dccp.h"
  13 #include <linux/kernel.h>
  14 #include <linux/slab.h>
  15 #include <linux/export.h>
  16
  17 static struct kmem_cache *dccp_ackvec_slab;
  18 static struct kmem_cache *dccp_ackvec_record_slab;
  19
  20 struct 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
  31 static 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
  40 void 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  */
  54 int 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
  88 static 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  */
 110 static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
 111 {
 112         return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
 113 }
 114
 115 static 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
 120 u16 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  */
 134 static 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". */
 177 static 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  */
 199 static 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  */
 249 void 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  */
 285 void 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
 340 free_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  */
 350 int 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 }
 363 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
 364
 365 void 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 }
 373 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
 374
 375 int __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
 391 out_destroy_slab:
 392         kmem_cache_destroy(dccp_ackvec_slab);
 393         dccp_ackvec_slab = NULL;
 394 out_err:
 395         DCCP_CRIT("Unable to create Ack Vector slab cache");
 396         return -ENOBUFS;
 397 }
 398
 399 void 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 }