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 } 409