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 /*
  96  * Buffer index and length computation using modulo-buffersize arithmetic.
  97  * Note that, as pointers move from right to left, head is `before' tail.
  98  */
  99 static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
 100 {
 101         return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
 102 }
 103
 104 static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
 105 {
 106         return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
 107 }
 108
 109 u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
 110 {
 111         if (unlikely(av->av_overflow))
 112                 return DCCPAV_MAX_ACKVEC_LEN;
 113         return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
 114 }
 115
 116 /*
 117  * If several packets are missing, the HC-Receiver may prefer to enter multiple
 118  * bytes with run length 0, rather than a single byte with a larger run length;
 119  * this simplifies table updates if one of the missing packets arrives.
 120  */
 121 static inline int dccp_ackvec_set_buf_head_state(struct dccp_ackvec *av,
 122                                                  const unsigned int packets,
 123                                                  const unsigned char state)
 124 {
 125         long gap;
 126         long new_head;
 127
 128         if (av->av_vec_len + packets > DCCPAV_MAX_ACKVEC_LEN)
 129                 return -ENOBUFS;
 130
 131         gap      = packets - 1;
 132         new_head = av->av_buf_head - packets;
 133
 134         if (new_head < 0) {
 135                 if (gap > 0) {
 136                         memset(av->av_buf, DCCPAV_NOT_RECEIVED,
 137                                gap + new_head + 1);
 138                         gap = -new_head;
 139                 }
 140                 new_head += DCCPAV_MAX_ACKVEC_LEN;
 141         }
 142
 143         av->av_buf_head = new_head;
 144
 145         if (gap > 0)
 146                 memset(av->av_buf + av->av_buf_head + 1,
 147                        DCCPAV_NOT_RECEIVED, gap);
 148
 149         av->av_buf[av->av_buf_head] = state;
 150         av->av_vec_len += packets;
 151         return 0;
 152 }
 153
 154 /*
 155  * Implements the RFC 4340, Appendix A
 156  */
 157 int dccp_ackvec_add(struct dccp_ackvec *av, const struct sock *sk,
 158                     const u64 ackno, const u8 state)
 159 {
 160         u8 *cur_head = av->av_buf + av->av_buf_head,
 161            *buf_end  = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;
 162         /*
 163          * Check at the right places if the buffer is full, if it is, tell the
 164          * caller to start dropping packets till the HC-Sender acks our ACK
 165          * vectors, when we will free up space in av_buf.
 166          *
 167          * We may well decide to do buffer compression, etc, but for now lets
 168          * just drop.
 169          *
 170          * From Appendix A.1.1 (`New Packets'):
 171          *
 172          *      Of course, the circular buffer may overflow, either when the
 173          *      HC-Sender is sending data at a very high rate, when the
 174          *      HC-Receiver's acknowledgements are not reaching the HC-Sender,
 175          *      or when the HC-Sender is forgetting to acknowledge those acks
 176          *      (so the HC-Receiver is unable to clean up old state). In this
 177          *      case, the HC-Receiver should either compress the buffer (by
 178          *      increasing run lengths when possible), transfer its state to
 179          *      a larger buffer, or, as a last resort, drop all received
 180          *      packets, without processing them whatsoever, until its buffer
 181          *      shrinks again.
 182          */
 183
 184         /* See if this is the first ackno being inserted */
 185         if (av->av_vec_len == 0) {
 186                 *cur_head = state;
 187                 av->av_vec_len = 1;
 188         } else if (after48(ackno, av->av_buf_ackno)) {
 189                 const u64 delta = dccp_delta_seqno(av->av_buf_ackno, ackno);
 190
 191                 /*
 192                  * Look if the state of this packet is the same as the
 193                  * previous ackno and if so if we can bump the head len.
 194                  */
 195                 if (delta == 1 && dccp_ackvec_state(cur_head) == state &&
 196                     dccp_ackvec_runlen(cur_head) < DCCPAV_MAX_RUNLEN)
 197                         *cur_head += 1;
 198                 else if (dccp_ackvec_set_buf_head_state(av, delta, state))
 199                         return -ENOBUFS;
 200         } else {
 201                 /*
 202                  * A.1.2.  Old Packets
 203                  *
 204                  *      When a packet with Sequence Number S <= buf_ackno
 205                  *      arrives, the HC-Receiver will scan the table for
 206                  *      the byte corresponding to S. (Indexing structures
 207                  *      could reduce the complexity of this scan.)
 208                  */
 209                 u64 delta = dccp_delta_seqno(ackno, av->av_buf_ackno);
 210
 211                 while (1) {
 212                         const u8 len = dccp_ackvec_runlen(cur_head);
 213                         /*
 214                          * valid packets not yet in av_buf have a reserved
 215                          * entry, with a len equal to 0.
 216                          */
 217                         if (*cur_head == DCCPAV_NOT_RECEIVED && delta == 0) {
 218                                 dccp_pr_debug("Found %llu reserved seat!\n",
 219                                               (unsigned long long)ackno);
 220                                 *cur_head = state;
 221                                 goto out;
 222                         }
 223                         /* len == 0 means one packet */
 224                         if (delta < len + 1)
 225                                 goto out_duplicate;
 226
 227                         delta -= len + 1;
 228                         if (++cur_head == buf_end)
 229                                 cur_head = av->av_buf;
 230                 }
 231         }
 232
 233         av->av_buf_ackno = ackno;
 234 out:
 235         return 0;
 236
 237 out_duplicate:
 238         /* Duplicate packet */
 239         dccp_pr_debug("Received a dup or already considered lost "
 240                       "packet: %llu\n", (unsigned long long)ackno);
 241         return -EILSEQ;
 242 }
 243
 244 static void dccp_ackvec_throw_record(struct dccp_ackvec *av,
 245                                      struct dccp_ackvec_record *avr)
 246 {
 247         struct dccp_ackvec_record *next;
 248
 249         /* sort out vector length */
 250         if (av->av_buf_head <= avr->avr_ack_ptr)
 251                 av->av_vec_len = avr->avr_ack_ptr - av->av_buf_head;
 252         else
 253                 av->av_vec_len = DCCPAV_MAX_ACKVEC_LEN - 1 -
 254                                  av->av_buf_head + avr->avr_ack_ptr;
 255
 256         /* free records */
 257         list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
 258                 list_del(&avr->avr_node);
 259                 kmem_cache_free(dccp_ackvec_record_slab, avr);
 260         }
 261 }
 262
 263 void dccp_ackvec_check_rcv_ackno(struct dccp_ackvec *av, struct sock *sk,
 264                                  const u64 ackno)
 265 {
 266         struct dccp_ackvec_record *avr;
 267
 268         /*
 269          * If we traverse backwards, it should be faster when we have large
 270          * windows. We will be receiving ACKs for stuff we sent a while back
 271          * -sorbo.
 272          */
 273         list_for_each_entry_reverse(avr, &av->av_records, avr_node) {
 274                 if (ackno == avr->avr_ack_seqno) {
 275                         dccp_pr_debug("%s ACK packet 0, len=%d, ack_seqno=%llu, "
 276                                       "ack_ackno=%llu, ACKED!\n",
 277                                       dccp_role(sk), avr->avr_ack_runlen,
 278                                       (unsigned long long)avr->avr_ack_seqno,
 279                                       (unsigned long long)avr->avr_ack_ackno);
 280                         dccp_ackvec_throw_record(av, avr);
 281                         break;
 282                 } else if (avr->avr_ack_seqno > ackno)
 283                         break; /* old news */
 284         }
 285 }
 286
 287 static void dccp_ackvec_check_rcv_ackvector(struct dccp_ackvec *av,
 288                                             struct sock *sk, u64 *ackno,
 289                                             const unsigned char len,
 290                                             const unsigned char *vector)
 291 {
 292         unsigned char i;
 293         struct dccp_ackvec_record *avr;
 294
 295         /* Check if we actually sent an ACK vector */
 296         if (list_empty(&av->av_records))
 297                 return;
 298
 299         i = len;
 300         /*
 301          * XXX
 302          * I think it might be more efficient to work backwards. See comment on
 303          * rcv_ackno. -sorbo.
 304          */
 305         avr = list_entry(av->av_records.next, struct dccp_ackvec_record, avr_node);
 306         while (i--) {
 307                 const u8 rl = dccp_ackvec_runlen(vector);
 308                 u64 ackno_end_rl;
 309
 310                 dccp_set_seqno(&ackno_end_rl, *ackno - rl);
 311
 312                 /*
 313                  * If our AVR sequence number is greater than the ack, go
 314                  * forward in the AVR list until it is not so.
 315                  */
 316                 list_for_each_entry_from(avr, &av->av_records, avr_node) {
 317                         if (!after48(avr->avr_ack_seqno, *ackno))
 318                                 goto found;
 319                 }
 320                 /* End of the av_records list, not found, exit */
 321                 break;
 322 found:
 323                 if (between48(avr->avr_ack_seqno, ackno_end_rl, *ackno)) {
 324                         if (dccp_ackvec_state(vector) != DCCPAV_NOT_RECEIVED) {
 325                                 dccp_pr_debug("%s ACK vector 0, len=%d, "
 326                                               "ack_seqno=%llu, ack_ackno=%llu, "
 327                                               "ACKED!\n",
 328                                               dccp_role(sk), len,
 329                                               (unsigned long long)
 330                                               avr->avr_ack_seqno,
 331                                               (unsigned long long)
 332                                               avr->avr_ack_ackno);
 333                                 dccp_ackvec_throw_record(av, avr);
 334                                 break;
 335                         }
 336                         /*
 337                          * If it wasn't received, continue scanning... we might
 338                          * find another one.
 339                          */
 340                 }
 341
 342                 dccp_set_seqno(ackno, ackno_end_rl - 1);
 343                 ++vector;
 344         }
 345 }
 346
 347 int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb,
 348                       u64 *ackno, const u8 opt, const u8 *value, const u8 len)
 349 {
 350         if (len > DCCP_SINGLE_OPT_MAXLEN)
 351                 return -1;
 352
 353         /* dccp_ackvector_print(DCCP_SKB_CB(skb)->dccpd_ack_seq, value, len); */
 354         dccp_ackvec_check_rcv_ackvector(dccp_sk(sk)->dccps_hc_rx_ackvec, sk,
 355                                         ackno, len, value);
 356         return 0;
 357 }
 358
 359 int __init dccp_ackvec_init(void)
 360 {
 361         dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
 362                                              sizeof(struct dccp_ackvec), 0,
 363                                              SLAB_HWCACHE_ALIGN, NULL);
 364         if (dccp_ackvec_slab == NULL)
 365                 goto out_err;
 366
 367         dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
 368                                              sizeof(struct dccp_ackvec_record),
 369                                              0, SLAB_HWCACHE_ALIGN, NULL);
 370         if (dccp_ackvec_record_slab == NULL)
 371                 goto out_destroy_slab;
 372
 373         return 0;
 374
 375 out_destroy_slab:
 376         kmem_cache_destroy(dccp_ackvec_slab);
 377         dccp_ackvec_slab = NULL;
 378 out_err:
 379         DCCP_CRIT("Unable to create Ack Vector slab cache");
 380         return -ENOBUFS;
 381 }
 382
 383 void dccp_ackvec_exit(void)
 384 {
 385         if (dccp_ackvec_slab != NULL) {
 386                 kmem_cache_destroy(dccp_ackvec_slab);
 387                 dccp_ackvec_slab = NULL;
 388         }
 389         if (dccp_ackvec_record_slab != NULL) {
 390                 kmem_cache_destroy(dccp_ackvec_record_slab);
 391                 dccp_ackvec_record_slab = NULL;
 392         }
 393 }