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