tcp/sack: Use RFC3517bis IsLost(snd_una) as fallback of early retransmit
[dragonfly.git] / sys / netinet / tcp_sack.c
1 /*
2  * Copyright (c) 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
3  * Copyright (c) 2003, 2004 The DragonFly Project.  All rights reserved.
4  *
5  * This code is derived from software contributed to The DragonFly Project
6  * by Jeffrey M. Hsu.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of The DragonFly Project nor the names of its
17  *    contributors may be used to endorse or promote products derived
18  *    from this software without specific, prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * $DragonFly: src/sys/netinet/tcp_sack.c,v 1.8 2008/08/15 21:37:16 nth Exp $
34  */
35
36 #include <sys/param.h>
37 #include <sys/systm.h>
38 #include <sys/kernel.h>
39 #include <sys/malloc.h>
40 #include <sys/queue.h>
41 #include <sys/thread.h>
42 #include <sys/types.h>
43 #include <sys/socket.h>
44 #include <sys/socketvar.h>
45
46 #include <net/if.h>
47
48 #include <netinet/in.h>
49 #include <netinet/in_systm.h>
50 #include <netinet/ip.h>
51 #include <netinet/in_var.h>
52 #include <netinet/in_pcb.h>
53 #include <netinet/ip_var.h>
54 #include <netinet/tcp.h>
55 #include <netinet/tcp_seq.h>
56 #include <netinet/tcp_var.h>
57
58 /*
59  * Implemented:
60  *
61  * RFC 2018
62  * RFC 2883
63  * RFC 3517
64  */
65
66 struct sackblock {
67         tcp_seq                 sblk_start;
68         tcp_seq                 sblk_end;
69         TAILQ_ENTRY(sackblock)  sblk_list;
70 };
71
72 #define MAXSAVEDBLOCKS  8                       /* per connection limit */
73
74 static int insert_block(struct scoreboard *scb,
75                         const struct raw_sackblock *raw_sb, boolean_t *update);
76
77 static MALLOC_DEFINE(M_SACKBLOCK, "sblk", "sackblock struct");
78
79 /*
80  * Per-tcpcb initialization.
81  */
82 void
83 tcp_sack_tcpcb_init(struct tcpcb *tp)
84 {
85         struct scoreboard *scb = &tp->scb;
86
87         scb->nblocks = 0;
88         TAILQ_INIT(&scb->sackblocks);
89         scb->lastfound = NULL;
90 }
91
92 /*
93  * Find the SACK block containing or immediately preceding "seq".
94  * The boolean result indicates whether the sequence is actually
95  * contained in the SACK block.
96  */
97 static boolean_t
98 sack_block_lookup(struct scoreboard *scb, tcp_seq seq, struct sackblock **sb)
99 {
100         struct sackblock *hint = scb->lastfound;
101         struct sackblock *cur, *last, *prev;
102
103         if (TAILQ_EMPTY(&scb->sackblocks)) {
104                 *sb = NULL;
105                 return FALSE;
106         }
107
108         if (hint == NULL) {
109                 /* No hint.  Search from start to end. */
110                 cur = TAILQ_FIRST(&scb->sackblocks);
111                 last = NULL;
112                 prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
113         } else  {
114                 if (SEQ_GEQ(seq, hint->sblk_start)) {
115                         /* Search from hint to end of list. */
116                         cur = hint;
117                         last = NULL;
118                         prev = TAILQ_LAST(&scb->sackblocks, sackblock_list);
119                 } else {
120                         /* Search from front of list to hint. */
121                         cur = TAILQ_FIRST(&scb->sackblocks);
122                         last = hint;
123                         prev = TAILQ_PREV(hint, sackblock_list, sblk_list);
124                 }
125         }
126
127         do {
128                 if (SEQ_GT(cur->sblk_end, seq)) {
129                         if (SEQ_GEQ(seq, cur->sblk_start)) {
130                                 *sb = scb->lastfound = cur;
131                                 return TRUE;
132                         } else {
133                                 *sb = scb->lastfound =
134                                     TAILQ_PREV(cur, sackblock_list, sblk_list);
135                                 return FALSE;
136                         }
137                 }
138                 cur = TAILQ_NEXT(cur, sblk_list);
139         } while (cur != last);
140
141         *sb = scb->lastfound = prev;
142         return FALSE;
143 }
144
145 /*
146  * Allocate a SACK block.
147  */
148 static __inline struct sackblock *
149 alloc_sackblock(struct scoreboard *scb, const struct raw_sackblock *raw_sb)
150 {
151         struct sackblock *sb;
152
153         if (scb->freecache != NULL) {
154                 sb = scb->freecache;
155                 scb->freecache = NULL;
156                 tcpstat.tcps_sacksbfast++;
157         } else {
158                 sb = kmalloc(sizeof(struct sackblock), M_SACKBLOCK, M_NOWAIT);
159                 if (sb == NULL) {
160                         tcpstat.tcps_sacksbfailed++;
161                         return NULL;
162                 }
163         }
164         sb->sblk_start = raw_sb->rblk_start;
165         sb->sblk_end = raw_sb->rblk_end;
166         return sb;
167 }
168
169 static __inline struct sackblock *
170 alloc_sackblock_limit(struct scoreboard *scb,
171     const struct raw_sackblock *raw_sb)
172 {
173         if (scb->nblocks == MAXSAVEDBLOCKS) {
174                 /*
175                  * Should try to kick out older blocks XXX JH
176                  * May be able to coalesce with existing block.
177                  * Or, go other way and free all blocks if we hit
178                  * this limit.
179                  */
180                 tcpstat.tcps_sacksboverflow++;
181                 return NULL;
182         }
183         return alloc_sackblock(scb, raw_sb);
184 }
185
186 /*
187  * Free a SACK block.
188  */
189 static __inline void
190 free_sackblock(struct scoreboard *scb, struct sackblock *s)
191 {
192         if (scb->freecache == NULL) {
193                 /* YYY Maybe use the latest freed block? */
194                 scb->freecache = s;
195                 return;
196         }
197         kfree(s, M_SACKBLOCK);
198 }
199
200 /*
201  * Free up SACK blocks for data that's been acked.
202  */
203 static void
204 tcp_sack_ack_blocks(struct scoreboard *scb, tcp_seq th_ack)
205 {
206         struct sackblock *sb, *nb;
207
208         sb = TAILQ_FIRST(&scb->sackblocks);
209         while (sb && SEQ_LEQ(sb->sblk_end, th_ack)) {
210                 nb = TAILQ_NEXT(sb, sblk_list);
211                 if (scb->lastfound == sb)
212                         scb->lastfound = NULL;
213                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
214                 free_sackblock(scb, sb);
215                 --scb->nblocks;
216                 KASSERT(scb->nblocks >= 0,
217                     ("SACK block count underflow: %d < 0", scb->nblocks));
218                 sb = nb;
219         }
220         if (sb && SEQ_GT(th_ack, sb->sblk_start))
221                 sb->sblk_start = th_ack;        /* other side reneged? XXX */
222 }
223
224 /*
225  * Delete and free SACK blocks saved in scoreboard.
226  */
227 void
228 tcp_sack_cleanup(struct scoreboard *scb)
229 {
230         struct sackblock *sb, *nb;
231
232         TAILQ_FOREACH_MUTABLE(sb, &scb->sackblocks, sblk_list, nb) {
233                 free_sackblock(scb, sb);
234                 --scb->nblocks;
235         }
236         KASSERT(scb->nblocks == 0,
237             ("SACK block %d count not zero", scb->nblocks));
238         TAILQ_INIT(&scb->sackblocks);
239         scb->lastfound = NULL;
240 }
241
242 /*
243  * Delete and free SACK blocks saved in scoreboard.
244  * Delete the one slot block cache.
245  */
246 void
247 tcp_sack_destroy(struct scoreboard *scb)
248 {
249         tcp_sack_cleanup(scb);
250         if (scb->freecache != NULL) {
251                 kfree(scb->freecache, M_SACKBLOCK);
252                 scb->freecache = NULL;
253         }
254 }
255
256 /*
257  * Cleanup the reported SACK block information
258  */
259 void
260 tcp_sack_report_cleanup(struct tcpcb *tp)
261 {
262         tp->sack_flags &=
263             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
264         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
265 }
266
267 /*
268  * Returns      0 if not D-SACK block,
269  *              1 if D-SACK,
270  *              2 if duplicate of out-of-order D-SACK block.
271  */
272 int
273 tcp_sack_ndsack_blocks(struct raw_sackblock *blocks, const int numblocks,
274                        tcp_seq snd_una)
275 {
276         if (numblocks == 0)
277                 return 0;
278
279         if (SEQ_LT(blocks[0].rblk_start, snd_una))
280                 return 1;
281
282         /* block 0 inside block 1 */
283         if (numblocks > 1 &&
284             SEQ_GEQ(blocks[0].rblk_start, blocks[1].rblk_start) &&
285             SEQ_LEQ(blocks[0].rblk_end, blocks[1].rblk_end))
286                 return 2;
287
288         return 0;
289 }
290
291 /*
292  * Update scoreboard on new incoming ACK.
293  */
294 static void
295 tcp_sack_add_blocks(struct tcpcb *tp, struct tcpopt *to)
296 {
297         const int numblocks = to->to_nsackblocks;
298         struct raw_sackblock *blocks = to->to_sackblocks;
299         struct scoreboard *scb = &tp->scb;
300         int startblock, i;
301
302         if (tcp_sack_ndsack_blocks(blocks, numblocks, tp->snd_una) > 0)
303                 startblock = 1;
304         else
305                 startblock = 0;
306
307         to->to_flags |= TOF_SACK_REDUNDANT;
308         for (i = startblock; i < numblocks; i++) {
309                 struct raw_sackblock *newsackblock = &blocks[i];
310                 boolean_t update;
311                 int error;
312
313                 /* Guard against ACK reordering */
314                 if (SEQ_LT(newsackblock->rblk_start, tp->snd_una))
315                         continue;
316
317                 /* Don't accept bad SACK blocks */
318                 if (SEQ_GT(newsackblock->rblk_end, tp->snd_max)) {
319                         tcpstat.tcps_rcvbadsackopt++;
320                         break;          /* skip all other blocks */
321                 }
322                 tcpstat.tcps_sacksbupdate++;
323
324                 error = insert_block(scb, newsackblock, &update);
325                 if (update)
326                         to->to_flags &= ~TOF_SACK_REDUNDANT;
327                 if (error)
328                         break;
329         }
330 }
331
332 void
333 tcp_sack_update_scoreboard(struct tcpcb *tp, struct tcpopt *to)
334 {
335         struct scoreboard *scb = &tp->scb;
336         int rexmt_high_update = 0;
337
338         tcp_sack_ack_blocks(scb, tp->snd_una);
339         tcp_sack_add_blocks(tp, to);
340         tcp_sack_update_lostseq(scb, tp->snd_una, tp->t_maxseg,
341             tp->t_rxtthresh);
342         if (SEQ_LT(tp->rexmt_high, tp->snd_una)) {
343                 tp->rexmt_high = tp->snd_una;
344                 rexmt_high_update = 1;
345         }
346         if (tp->sack_flags & TSACK_F_SACKRESCUED) {
347                 if (SEQ_LT(tp->rexmt_rescue, tp->snd_una)) {
348                         tp->sack_flags &= ~TSACK_F_SACKRESCUED;
349                 } else if (tcp_aggressive_rescuesack && rexmt_high_update &&
350                     SEQ_LT(tp->rexmt_rescue, tp->rexmt_high)) {
351                         /* Drag RescueRxt along with HighRxt */
352                         tp->rexmt_rescue = tp->rexmt_high;
353                 }
354         }
355 }
356
357 /*
358  * Insert SACK block into sender's scoreboard.
359  */
360 static int
361 insert_block(struct scoreboard *scb, const struct raw_sackblock *raw_sb,
362     boolean_t *update)
363 {
364         struct sackblock *sb, *workingblock;
365         boolean_t overlap_front;
366
367         *update = TRUE;
368         if (TAILQ_EMPTY(&scb->sackblocks)) {
369                 struct sackblock *newblock;
370
371                 KASSERT(scb->nblocks == 0, ("emply scb w/ blocks"));
372
373                 newblock = alloc_sackblock(scb, raw_sb);
374                 if (newblock == NULL)
375                         return ENOMEM;
376                 TAILQ_INSERT_HEAD(&scb->sackblocks, newblock, sblk_list);
377                 scb->nblocks = 1;
378                 return 0;
379         }
380
381         KASSERT(scb->nblocks > 0, ("insert_block() called w/ no blocks"));
382         KASSERT(scb->nblocks <= MAXSAVEDBLOCKS,
383             ("too many SACK blocks %d", scb->nblocks));
384
385         overlap_front = sack_block_lookup(scb, raw_sb->rblk_start, &sb);
386
387         if (sb == NULL) {
388                 workingblock = alloc_sackblock_limit(scb, raw_sb);
389                 if (workingblock == NULL)
390                         return ENOMEM;
391                 TAILQ_INSERT_HEAD(&scb->sackblocks, workingblock, sblk_list);
392                 ++scb->nblocks;
393         } else {
394                 if (overlap_front || sb->sblk_end == raw_sb->rblk_start) {
395                         tcpstat.tcps_sacksbreused++;
396
397                         /* Extend old block */
398                         workingblock = sb;
399                         if (SEQ_GT(raw_sb->rblk_end, sb->sblk_end)) {
400                                 sb->sblk_end = raw_sb->rblk_end;
401                         } else {
402                                 /* Exact match, nothing to consolidate */
403                                 *update = FALSE;
404                                 return 0;
405                         }
406                 } else {
407                         workingblock = alloc_sackblock_limit(scb, raw_sb);
408                         if (workingblock == NULL)
409                                 return ENOMEM;
410                         TAILQ_INSERT_AFTER(&scb->sackblocks, sb, workingblock,
411                             sblk_list);
412                         ++scb->nblocks;
413                 }
414         }
415
416         /* Consolidate right-hand side. */
417         sb = TAILQ_NEXT(workingblock, sblk_list);
418         while (sb != NULL &&
419             SEQ_GEQ(workingblock->sblk_end, sb->sblk_end)) {
420                 struct sackblock *nextblock;
421
422                 nextblock = TAILQ_NEXT(sb, sblk_list);
423                 if (scb->lastfound == sb)
424                         scb->lastfound = NULL;
425                 /* Remove completely overlapped block */
426                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
427                 free_sackblock(scb, sb);
428                 --scb->nblocks;
429                 KASSERT(scb->nblocks > 0,
430                     ("removed overlapped block: %d blocks left", scb->nblocks));
431                 sb = nextblock;
432         }
433         if (sb != NULL &&
434             SEQ_GEQ(workingblock->sblk_end, sb->sblk_start)) {
435                 /* Extend new block to cover partially overlapped old block. */
436                 workingblock->sblk_end = sb->sblk_end;
437                 if (scb->lastfound == sb)
438                         scb->lastfound = NULL;
439                 TAILQ_REMOVE(&scb->sackblocks, sb, sblk_list);
440                 free_sackblock(scb, sb);
441                 --scb->nblocks;
442                 KASSERT(scb->nblocks > 0,
443                     ("removed partial right: %d blocks left", scb->nblocks));
444         }
445         return 0;
446 }
447
448 #ifdef DEBUG_SACK_BLOCKS
449 static void
450 tcp_sack_dump_blocks(struct scoreboard *scb)
451 {
452         struct sackblock *sb;
453
454         kprintf("%d blocks:", scb->nblocks);
455         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
456                 kprintf(" [%u, %u)", sb->sblk_start, sb->sblk_end);
457         kprintf("\n");
458 }
459 #else
460 static __inline void
461 tcp_sack_dump_blocks(struct scoreboard *scb)
462 {
463 }
464 #endif
465
466 /*
467  * Optimization to quickly determine which packets are lost.
468  */
469 void
470 tcp_sack_update_lostseq(struct scoreboard *scb, tcp_seq snd_una, u_int maxseg,
471     int rxtthresh)
472 {
473         struct sackblock *sb;
474         int nsackblocks = 0;
475         int bytes_sacked = 0;
476         int rxtthresh_bytes;
477
478         if (tcp_do_rfc3517bis)
479                 rxtthresh_bytes = (rxtthresh - 1) * maxseg;
480         else
481                 rxtthresh_bytes = rxtthresh * maxseg;
482
483         sb = TAILQ_LAST(&scb->sackblocks, sackblock_list);
484         while (sb != NULL) {
485                 ++nsackblocks;
486                 bytes_sacked += sb->sblk_end - sb->sblk_start;
487                 if (nsackblocks == rxtthresh ||
488                     bytes_sacked >= rxtthresh_bytes) {
489                         scb->lostseq = sb->sblk_start;
490                         return;
491                 }
492                 sb = TAILQ_PREV(sb, sackblock_list, sblk_list);
493         }
494         scb->lostseq = snd_una;
495 }
496
497 /*
498  * Return whether the given sequence number is considered lost.
499  */
500 boolean_t
501 tcp_sack_islost(struct scoreboard *scb, tcp_seq seqnum)
502 {
503         return SEQ_LT(seqnum, scb->lostseq);
504 }
505
506 /*
507  * True if at least "amount" has been SACKed.  Used by Early Retransmit.
508  */
509 boolean_t
510 tcp_sack_has_sacked(struct scoreboard *scb, u_int amount)
511 {
512         struct sackblock *sb;
513         int bytes_sacked = 0;
514
515         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
516                 bytes_sacked += sb->sblk_end - sb->sblk_start;
517                 if (bytes_sacked >= amount)
518                         return TRUE;
519         }
520         return FALSE;
521 }
522
523 /*
524  * Number of bytes SACKed below seq.
525  */
526 int
527 tcp_sack_bytes_below(struct scoreboard *scb, tcp_seq seq)
528 {
529         struct sackblock *sb;
530         int bytes_sacked = 0;
531
532         sb = TAILQ_FIRST(&scb->sackblocks);
533         while (sb && SEQ_GT(seq, sb->sblk_start)) {
534                 bytes_sacked += seq_min(seq, sb->sblk_end) - sb->sblk_start;
535                 sb = TAILQ_NEXT(sb, sblk_list);
536         }
537         return bytes_sacked;
538 }
539
540 /*
541  * Return estimate of the number of bytes outstanding in the network.
542  */
543 uint32_t
544 tcp_sack_compute_pipe(struct tcpcb *tp)
545 {
546         struct scoreboard *scb = &tp->scb;
547         struct sackblock *sb;
548         int nlost, nretransmitted;
549         tcp_seq end;
550
551         nlost = tp->snd_max - scb->lostseq;
552         nretransmitted = tp->rexmt_high - tp->snd_una;
553
554         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list) {
555                 if (SEQ_LT(sb->sblk_start, tp->rexmt_high)) {
556                         end = seq_min(sb->sblk_end, tp->rexmt_high);
557                         nretransmitted -= end - sb->sblk_start;
558                 }
559                 if (SEQ_GEQ(sb->sblk_start, scb->lostseq))
560                         nlost -= sb->sblk_end - sb->sblk_start;
561         }
562
563         return (nlost + nretransmitted);
564 }
565
566 /*
567  * Return the sequence number and length of the next segment to transmit
568  * when in Fast Recovery.
569  */
570 boolean_t
571 tcp_sack_nextseg(struct tcpcb *tp, tcp_seq *nextrexmt, uint32_t *plen,
572     boolean_t *rescue)
573 {
574         struct scoreboard *scb = &tp->scb;
575         struct socket *so = tp->t_inpcb->inp_socket;
576         struct sackblock *sb;
577         const struct sackblock *lastblock =
578             TAILQ_LAST(&scb->sackblocks, sackblock_list);
579         tcp_seq torexmt;
580         long len, off;
581
582         /* skip SACKed data */
583         tcp_sack_skip_sacked(scb, &tp->rexmt_high);
584
585         /* Look for lost data. */
586         torexmt = tp->rexmt_high;
587         *rescue = FALSE;
588         if (lastblock != NULL) {
589                 if (SEQ_LT(torexmt, lastblock->sblk_end) &&
590                     tcp_sack_islost(scb, torexmt)) {
591 sendunsacked:
592                         *nextrexmt = torexmt;
593                         /* If the left-hand edge has been SACKed, pull it in. */
594                         if (sack_block_lookup(scb, torexmt + tp->t_maxseg, &sb))
595                                 *plen = sb->sblk_start - torexmt;
596                         else
597                                 *plen = tp->t_maxseg;
598                         return TRUE;
599                 }
600         }
601
602         /* See if unsent data available within send window. */
603         off = tp->snd_max - tp->snd_una;
604         len = (long) ulmin(so->so_snd.ssb_cc, tp->snd_wnd) - off;
605         if (len > 0) {
606                 *nextrexmt = tp->snd_max;       /* Send new data. */
607                 *plen = tp->t_maxseg;
608                 return TRUE;
609         }
610
611         /* We're less certain this data has been lost. */
612         if (lastblock != NULL && SEQ_LT(torexmt, lastblock->sblk_end))
613                 goto sendunsacked;
614
615         /* Rescue retransmission */
616         if (tcp_do_rescuesack || tcp_do_rfc3517bis) {
617                 tcpstat.tcps_sackrescue_try++;
618                 if (tp->sack_flags & TSACK_F_SACKRESCUED) {
619                         if (!tcp_aggressive_rescuesack)
620                                 return FALSE;
621
622                         /*
623                          * Aggressive variant of the rescue retransmission.
624                          *
625                          * The idea of the rescue retransmission is to sustain
626                          * the ACK clock thus to avoid timeout retransmission.
627                          *
628                          * Under some situations, the conservative approach
629                          * suggested in the draft
630                          * http://tools.ietf.org/html/
631                          * draft-nishida-tcpm-rescue-retransmission-00
632                          * could not sustain ACK clock, since it only allows
633                          * one rescue retransmission before a cumulative ACK
634                          * covers the segement transmitted by rescue
635                          * retransmission.
636                          *
637                          * We try to locate the next unSACKed segment which
638                          * follows the previously sent rescue segment.  If
639                          * there is no such segment, we loop back to the first
640                          * unacknowledged segment.
641                          */
642
643                         /*
644                          * Skip SACKed data, but here we follow
645                          * the last transmitted rescue segment.
646                          */
647                         torexmt = tp->rexmt_rescue;
648                         tcp_sack_skip_sacked(scb, &torexmt);
649                 }
650                 if (torexmt == tp->snd_max) {
651                         /* Nothing left to retransmit; restart */
652                         torexmt = tp->snd_una;
653                 }
654                 *rescue = TRUE;
655                 goto sendunsacked;
656         } else if (tcp_do_smartsack && lastblock == NULL) {
657                 tcpstat.tcps_sackrescue_try++;
658                 *rescue = TRUE;
659                 goto sendunsacked;
660         }
661
662         return FALSE;
663 }
664
665 /*
666  * Return the next sequence number higher than "*prexmt" that has
667  * not been SACKed.
668  */
669 void
670 tcp_sack_skip_sacked(struct scoreboard *scb, tcp_seq *prexmt)
671 {
672         struct sackblock *sb;
673
674         /* skip SACKed data */
675         if (sack_block_lookup(scb, *prexmt, &sb))
676                 *prexmt = sb->sblk_end;
677 }
678
679 #ifdef later
680 void
681 tcp_sack_save_scoreboard(struct scoreboard *scb)
682 {
683         struct scoreboard *scb = &tp->scb;
684
685         scb->sackblocks_prev = scb->sackblocks;
686         TAILQ_INIT(&scb->sackblocks);
687 }
688
689 void
690 tcp_sack_revert_scoreboard(struct scoreboard *scb, tcp_seq snd_una,
691                            u_int maxseg)
692 {
693         struct sackblock *sb;
694
695         scb->sackblocks = scb->sackblocks_prev;
696         scb->nblocks = 0;
697         TAILQ_FOREACH(sb, &scb->sackblocks, sblk_list)
698                 ++scb->nblocks;
699         tcp_sack_ack_blocks(scb, snd_una);
700         scb->lastfound = NULL;
701 }
702 #endif
703
704 #ifdef DEBUG_SACK_HISTORY
705 static void
706 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
707 {
708         int i;
709         static int ndumped;
710
711         /* only need a couple of these to debug most problems */
712         if (++ndumped > 900)
713                 return;
714
715         kprintf("%s:\tnsackhistory %d: ", msg, tp->nsackhistory);
716         for (i = 0; i < tp->nsackhistory; ++i)
717                 kprintf("[%u, %u) ", tp->sackhistory[i].rblk_start,
718                     tp->sackhistory[i].rblk_end);
719         kprintf("\n");
720 }
721 #else
722 static __inline void
723 tcp_sack_dump_history(char *msg, struct tcpcb *tp)
724 {
725 }
726 #endif
727
728 /*
729  * Remove old SACK blocks from the SACK history that have already been ACKed.
730  */
731 static void
732 tcp_sack_ack_history(struct tcpcb *tp)
733 {
734         int i, nblocks, openslot;
735
736         tcp_sack_dump_history("before tcp_sack_ack_history", tp);
737         nblocks = tp->nsackhistory;
738         for (i = openslot = 0; i < nblocks; ++i) {
739                 if (SEQ_LEQ(tp->sackhistory[i].rblk_end, tp->rcv_nxt)) {
740                         --tp->nsackhistory;
741                         continue;
742                 }
743                 if (SEQ_LT(tp->sackhistory[i].rblk_start, tp->rcv_nxt))
744                         tp->sackhistory[i].rblk_start = tp->rcv_nxt;
745                 if (i == openslot)
746                         ++openslot;
747                 else
748                         tp->sackhistory[openslot++] = tp->sackhistory[i];
749         }
750         tcp_sack_dump_history("after tcp_sack_ack_history", tp);
751         KASSERT(openslot == tp->nsackhistory,
752             ("tcp_sack_ack_history miscounted: %d != %d",
753             openslot, tp->nsackhistory));
754 }
755
756 /*
757  * Add or merge newblock into reported history.
758  * Also remove or update SACK blocks that will be acked.
759  */
760 static void
761 tcp_sack_update_reported_history(struct tcpcb *tp, tcp_seq start, tcp_seq end)
762 {
763         struct raw_sackblock copy[MAX_SACK_REPORT_BLOCKS];
764         int i, cindex;
765
766         tcp_sack_dump_history("before tcp_sack_update_reported_history", tp);
767         /*
768          * Six cases:
769          *      0) no overlap
770          *      1) newblock == oldblock
771          *      2) oldblock contains newblock
772          *      3) newblock contains oldblock
773          *      4) tail of oldblock overlaps or abuts start of newblock
774          *      5) tail of newblock overlaps or abuts head of oldblock
775          */
776         for (i = cindex = 0; i < tp->nsackhistory; ++i) {
777                 struct raw_sackblock *oldblock = &tp->sackhistory[i];
778                 tcp_seq old_start = oldblock->rblk_start;
779                 tcp_seq old_end = oldblock->rblk_end;
780
781                 if (SEQ_LT(end, old_start) || SEQ_GT(start, old_end)) {
782                         /* Case 0:  no overlap.  Copy old block. */
783                         copy[cindex++] = *oldblock;
784                         continue;
785                 }
786
787                 if (SEQ_GEQ(start, old_start) && SEQ_LEQ(end, old_end)) {
788                         /* Cases 1 & 2.  Move block to front of history. */
789                         int j;
790
791                         start = old_start;
792                         end = old_end;
793                         /* no need to check rest of blocks */
794                         for (j = i + 1; j < tp->nsackhistory; ++j)
795                                 copy[cindex++] = tp->sackhistory[j];
796                         break;
797                 }
798
799                 if (SEQ_GEQ(old_end, start) && SEQ_LT(old_start, start)) {
800                         /* Case 4:  extend start of new block. */
801                         start = old_start;
802                 } else if (SEQ_GEQ(end, old_start) && SEQ_GT(old_end, end)) {
803                         /* Case 5: extend end of new block */
804                         end = old_end;
805                 } else {
806                         /* Case 3.  Delete old block by not copying it. */
807                         KASSERT(SEQ_LEQ(start, old_start) &&
808                                 SEQ_GEQ(end, old_end),
809                             ("bad logic: old [%u, %u), new [%u, %u)",
810                              old_start, old_end, start, end));
811                 }
812         }
813
814         /* insert new block */
815         tp->sackhistory[0].rblk_start = start;
816         tp->sackhistory[0].rblk_end = end;
817         cindex = min(cindex, MAX_SACK_REPORT_BLOCKS - 1);
818         for (i = 0; i < cindex; ++i)
819                 tp->sackhistory[i + 1] = copy[i];
820         tp->nsackhistory = cindex + 1;
821         tcp_sack_dump_history("after tcp_sack_update_reported_history", tp);
822 }
823
824 /*
825  * Fill in SACK report to return to data sender.
826  */
827 void
828 tcp_sack_fill_report(struct tcpcb *tp, u_char *opt, u_int *plen)
829 {
830         u_int optlen = *plen;
831         uint32_t *lp = (uint32_t *)(opt + optlen);
832         uint32_t *olp;
833         tcp_seq hstart = tp->rcv_nxt, hend;
834         int nblocks;
835
836         KASSERT(TCP_MAXOLEN - optlen >=
837             TCPOLEN_SACK_ALIGNED + TCPOLEN_SACK_BLOCK,
838             ("no room for SACK header and one block: optlen %d", optlen));
839
840         if (tp->sack_flags & TSACK_F_DUPSEG)
841                 tcpstat.tcps_snddsackopt++;
842         else
843                 tcpstat.tcps_sndsackopt++;
844
845         olp = lp++;
846         optlen += TCPOLEN_SACK_ALIGNED;
847
848         tcp_sack_ack_history(tp);
849         if (tp->reportblk.rblk_start != tp->reportblk.rblk_end) {
850                 *lp++ = htonl(tp->reportblk.rblk_start);
851                 *lp++ = htonl(tp->reportblk.rblk_end);
852                 optlen += TCPOLEN_SACK_BLOCK;
853                 hstart = tp->reportblk.rblk_start;
854                 hend = tp->reportblk.rblk_end;
855                 if (tp->sack_flags & TSACK_F_ENCLOSESEG) {
856                         KASSERT(TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK,
857                             ("no room for enclosing SACK block: oplen %d",
858                             optlen));
859                         *lp++ = htonl(tp->encloseblk.rblk_start);
860                         *lp++ = htonl(tp->encloseblk.rblk_end);
861                         optlen += TCPOLEN_SACK_BLOCK;
862                         hstart = tp->encloseblk.rblk_start;
863                         hend = tp->encloseblk.rblk_end;
864                 }
865                 if (SEQ_GT(hstart, tp->rcv_nxt))
866                         tcp_sack_update_reported_history(tp, hstart, hend);
867         }
868         if (tcp_do_smartsack && (tp->sack_flags & TSACK_F_SACKLEFT)) {
869                 /* Fill in from left!  Walk re-assembly queue. */
870                 struct tseg_qent *q;
871
872                 q = TAILQ_FIRST(&tp->t_segq);
873                 while (q != NULL &&
874                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
875                         *lp++ = htonl(q->tqe_th->th_seq);
876                         *lp++ = htonl(TCP_SACK_BLKEND(
877                             q->tqe_th->th_seq + q->tqe_len,
878                             q->tqe_th->th_flags));
879                         optlen += TCPOLEN_SACK_BLOCK;
880                         q = TAILQ_NEXT(q, tqe_q);
881                 }
882         } else {
883                 int n = 0;
884
885                 /* Fill in SACK blocks from right side. */
886                 while (n < tp->nsackhistory &&
887                     TCP_MAXOLEN - optlen >= TCPOLEN_SACK_BLOCK) {
888                         if (tp->sackhistory[n].rblk_start != hstart) {
889                                 *lp++ = htonl(tp->sackhistory[n].rblk_start);
890                                 *lp++ = htonl(tp->sackhistory[n].rblk_end);
891                                 optlen += TCPOLEN_SACK_BLOCK;
892                         }
893                         ++n;
894                 }
895         }
896         tp->reportblk.rblk_start = tp->reportblk.rblk_end;
897         tp->sack_flags &=
898             ~(TSACK_F_DUPSEG | TSACK_F_ENCLOSESEG | TSACK_F_SACKLEFT);
899         nblocks = (lp - olp - 1) / 2;
900         *olp = htonl(TCPOPT_SACK_ALIGNED |
901                      (TCPOLEN_SACK + nblocks * TCPOLEN_SACK_BLOCK));
902         *plen = optlen;
903 }