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Linux/net/dccp/ackvec.c

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  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_t(u32, lost_packets, 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");
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         kmem_cache_destroy(dccp_ackvec_slab);
402         dccp_ackvec_slab = NULL;
403         kmem_cache_destroy(dccp_ackvec_record_slab);
404         dccp_ackvec_record_slab = NULL;
405 }
406 

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