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 } 410