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TOMOYO Linux Cross Reference
Linux/net/dccp/ccids/ccid2.c

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  1 /*
  2  *  Copyright (c) 2005, 2006 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
  3  *
  4  *  Changes to meet Linux coding standards, and DCCP infrastructure fixes.
  5  *
  6  *  Copyright (c) 2006 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  7  *
  8  *  This program is free software; you can redistribute it and/or modify
  9  *  it under the terms of the GNU General Public License as published by
 10  *  the Free Software Foundation; either version 2 of the License, or
 11  *  (at your option) any later version.
 12  *
 13  *  This program is distributed in the hope that it will be useful,
 14  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 15  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 16  *  GNU General Public License for more details.
 17  *
 18  *  You should have received a copy of the GNU General Public License
 19  *  along with this program; if not, write to the Free Software
 20  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 21  */
 22 
 23 /*
 24  * This implementation should follow RFC 4341
 25  */
 26 #include <linux/slab.h>
 27 #include "../feat.h"
 28 #include "ccid2.h"
 29 
 30 
 31 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
 32 static bool ccid2_debug;
 33 #define ccid2_pr_debug(format, a...)    DCCP_PR_DEBUG(ccid2_debug, format, ##a)
 34 #else
 35 #define ccid2_pr_debug(format, a...)
 36 #endif
 37 
 38 static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hc)
 39 {
 40         struct ccid2_seq *seqp;
 41         int i;
 42 
 43         /* check if we have space to preserve the pointer to the buffer */
 44         if (hc->tx_seqbufc >= (sizeof(hc->tx_seqbuf) /
 45                                sizeof(struct ccid2_seq *)))
 46                 return -ENOMEM;
 47 
 48         /* allocate buffer and initialize linked list */
 49         seqp = kmalloc(CCID2_SEQBUF_LEN * sizeof(struct ccid2_seq), gfp_any());
 50         if (seqp == NULL)
 51                 return -ENOMEM;
 52 
 53         for (i = 0; i < (CCID2_SEQBUF_LEN - 1); i++) {
 54                 seqp[i].ccid2s_next = &seqp[i + 1];
 55                 seqp[i + 1].ccid2s_prev = &seqp[i];
 56         }
 57         seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = seqp;
 58         seqp->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
 59 
 60         /* This is the first allocation.  Initiate the head and tail.  */
 61         if (hc->tx_seqbufc == 0)
 62                 hc->tx_seqh = hc->tx_seqt = seqp;
 63         else {
 64                 /* link the existing list with the one we just created */
 65                 hc->tx_seqh->ccid2s_next = seqp;
 66                 seqp->ccid2s_prev = hc->tx_seqh;
 67 
 68                 hc->tx_seqt->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
 69                 seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = hc->tx_seqt;
 70         }
 71 
 72         /* store the original pointer to the buffer so we can free it */
 73         hc->tx_seqbuf[hc->tx_seqbufc] = seqp;
 74         hc->tx_seqbufc++;
 75 
 76         return 0;
 77 }
 78 
 79 static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 80 {
 81         if (ccid2_cwnd_network_limited(ccid2_hc_tx_sk(sk)))
 82                 return CCID_PACKET_WILL_DEQUEUE_LATER;
 83         return CCID_PACKET_SEND_AT_ONCE;
 84 }
 85 
 86 static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
 87 {
 88         u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);
 89 
 90         /*
 91          * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
 92          * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
 93          * acceptable since this causes starvation/deadlock whenever cwnd < 2.
 94          * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
 95          */
 96         if (val == 0 || val > max_ratio) {
 97                 DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
 98                 val = max_ratio;
 99         }
100         dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
101                                    min_t(u32, val, DCCPF_ACK_RATIO_MAX));
102 }
103 
104 static void ccid2_check_l_ack_ratio(struct sock *sk)
105 {
106         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
107 
108         /*
109          * After a loss, idle period, application limited period, or RTO we
110          * need to check that the ack ratio is still less than the congestion
111          * window. Otherwise, we will send an entire congestion window of
112          * packets and got no response because we haven't sent ack ratio
113          * packets yet.
114          * If the ack ratio does need to be reduced, we reduce it to half of
115          * the congestion window (or 1 if that's zero) instead of to the
116          * congestion window. This prevents problems if one ack is lost.
117          */
118         if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
119                 ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
120 }
121 
122 static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
123 {
124         dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
125                                    clamp_val(val, DCCPF_SEQ_WMIN,
126                                                   DCCPF_SEQ_WMAX));
127 }
128 
129 static void ccid2_hc_tx_rto_expire(unsigned long data)
130 {
131         struct sock *sk = (struct sock *)data;
132         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
133         const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
134 
135         bh_lock_sock(sk);
136         if (sock_owned_by_user(sk)) {
137                 sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
138                 goto out;
139         }
140 
141         ccid2_pr_debug("RTO_EXPIRE\n");
142 
143         /* back-off timer */
144         hc->tx_rto <<= 1;
145         if (hc->tx_rto > DCCP_RTO_MAX)
146                 hc->tx_rto = DCCP_RTO_MAX;
147 
148         /* adjust pipe, cwnd etc */
149         hc->tx_ssthresh = hc->tx_cwnd / 2;
150         if (hc->tx_ssthresh < 2)
151                 hc->tx_ssthresh = 2;
152         hc->tx_cwnd     = 1;
153         hc->tx_pipe     = 0;
154 
155         /* clear state about stuff we sent */
156         hc->tx_seqt = hc->tx_seqh;
157         hc->tx_packets_acked = 0;
158 
159         /* clear ack ratio state. */
160         hc->tx_rpseq    = 0;
161         hc->tx_rpdupack = -1;
162         ccid2_change_l_ack_ratio(sk, 1);
163 
164         /* if we were blocked before, we may now send cwnd=1 packet */
165         if (sender_was_blocked)
166                 tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
167         /* restart backed-off timer */
168         sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
169 out:
170         bh_unlock_sock(sk);
171         sock_put(sk);
172 }
173 
174 /*
175  *      Congestion window validation (RFC 2861).
176  */
177 static bool ccid2_do_cwv = true;
178 module_param(ccid2_do_cwv, bool, 0644);
179 MODULE_PARM_DESC(ccid2_do_cwv, "Perform RFC2861 Congestion Window Validation");
180 
181 /**
182  * ccid2_update_used_window  -  Track how much of cwnd is actually used
183  * This is done in addition to CWV. The sender needs to have an idea of how many
184  * packets may be in flight, to set the local Sequence Window value accordingly
185  * (RFC 4340, 7.5.2). The CWV mechanism is exploited to keep track of the
186  * maximum-used window. We use an EWMA low-pass filter to filter out noise.
187  */
188 static void ccid2_update_used_window(struct ccid2_hc_tx_sock *hc, u32 new_wnd)
189 {
190         hc->tx_expected_wnd = (3 * hc->tx_expected_wnd + new_wnd) / 4;
191 }
192 
193 /* This borrows the code of tcp_cwnd_application_limited() */
194 static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
195 {
196         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
197         /* don't reduce cwnd below the initial window (IW) */
198         u32 init_win = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache),
199             win_used = max(hc->tx_cwnd_used, init_win);
200 
201         if (win_used < hc->tx_cwnd) {
202                 hc->tx_ssthresh = max(hc->tx_ssthresh,
203                                      (hc->tx_cwnd >> 1) + (hc->tx_cwnd >> 2));
204                 hc->tx_cwnd = (hc->tx_cwnd + win_used) >> 1;
205         }
206         hc->tx_cwnd_used  = 0;
207         hc->tx_cwnd_stamp = now;
208 
209         ccid2_check_l_ack_ratio(sk);
210 }
211 
212 /* This borrows the code of tcp_cwnd_restart() */
213 static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
214 {
215         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
216         u32 cwnd = hc->tx_cwnd, restart_cwnd,
217             iwnd = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache);
218 
219         hc->tx_ssthresh = max(hc->tx_ssthresh, (cwnd >> 1) + (cwnd >> 2));
220 
221         /* don't reduce cwnd below the initial window (IW) */
222         restart_cwnd = min(cwnd, iwnd);
223         cwnd >>= (now - hc->tx_lsndtime) / hc->tx_rto;
224         hc->tx_cwnd = max(cwnd, restart_cwnd);
225 
226         hc->tx_cwnd_stamp = now;
227         hc->tx_cwnd_used  = 0;
228 
229         ccid2_check_l_ack_ratio(sk);
230 }
231 
232 static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
233 {
234         struct dccp_sock *dp = dccp_sk(sk);
235         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
236         const u32 now = ccid2_time_stamp;
237         struct ccid2_seq *next;
238 
239         /* slow-start after idle periods (RFC 2581, RFC 2861) */
240         if (ccid2_do_cwv && !hc->tx_pipe &&
241             (s32)(now - hc->tx_lsndtime) >= hc->tx_rto)
242                 ccid2_cwnd_restart(sk, now);
243 
244         hc->tx_lsndtime = now;
245         hc->tx_pipe    += 1;
246 
247         /* see whether cwnd was fully used (RFC 2861), update expected window */
248         if (ccid2_cwnd_network_limited(hc)) {
249                 ccid2_update_used_window(hc, hc->tx_cwnd);
250                 hc->tx_cwnd_used  = 0;
251                 hc->tx_cwnd_stamp = now;
252         } else {
253                 if (hc->tx_pipe > hc->tx_cwnd_used)
254                         hc->tx_cwnd_used = hc->tx_pipe;
255 
256                 ccid2_update_used_window(hc, hc->tx_cwnd_used);
257 
258                 if (ccid2_do_cwv && (s32)(now - hc->tx_cwnd_stamp) >= hc->tx_rto)
259                         ccid2_cwnd_application_limited(sk, now);
260         }
261 
262         hc->tx_seqh->ccid2s_seq   = dp->dccps_gss;
263         hc->tx_seqh->ccid2s_acked = 0;
264         hc->tx_seqh->ccid2s_sent  = now;
265 
266         next = hc->tx_seqh->ccid2s_next;
267         /* check if we need to alloc more space */
268         if (next == hc->tx_seqt) {
269                 if (ccid2_hc_tx_alloc_seq(hc)) {
270                         DCCP_CRIT("packet history - out of memory!");
271                         /* FIXME: find a more graceful way to bail out */
272                         return;
273                 }
274                 next = hc->tx_seqh->ccid2s_next;
275                 BUG_ON(next == hc->tx_seqt);
276         }
277         hc->tx_seqh = next;
278 
279         ccid2_pr_debug("cwnd=%d pipe=%d\n", hc->tx_cwnd, hc->tx_pipe);
280 
281         /*
282          * FIXME: The code below is broken and the variables have been removed
283          * from the socket struct. The `ackloss' variable was always set to 0,
284          * and with arsent there are several problems:
285          *  (i) it doesn't just count the number of Acks, but all sent packets;
286          *  (ii) it is expressed in # of packets, not # of windows, so the
287          *  comparison below uses the wrong formula: Appendix A of RFC 4341
288          *  comes up with the number K = cwnd / (R^2 - R) of consecutive windows
289          *  of data with no lost or marked Ack packets. If arsent were the # of
290          *  consecutive Acks received without loss, then Ack Ratio needs to be
291          *  decreased by 1 when
292          *            arsent >=  K * cwnd / R  =  cwnd^2 / (R^3 - R^2)
293          *  where cwnd / R is the number of Acks received per window of data
294          *  (cf. RFC 4341, App. A). The problems are that
295          *  - arsent counts other packets as well;
296          *  - the comparison uses a formula different from RFC 4341;
297          *  - computing a cubic/quadratic equation each time is too complicated.
298          *  Hence a different algorithm is needed.
299          */
300 #if 0
301         /* Ack Ratio.  Need to maintain a concept of how many windows we sent */
302         hc->tx_arsent++;
303         /* We had an ack loss in this window... */
304         if (hc->tx_ackloss) {
305                 if (hc->tx_arsent >= hc->tx_cwnd) {
306                         hc->tx_arsent  = 0;
307                         hc->tx_ackloss = 0;
308                 }
309         } else {
310                 /* No acks lost up to now... */
311                 /* decrease ack ratio if enough packets were sent */
312                 if (dp->dccps_l_ack_ratio > 1) {
313                         /* XXX don't calculate denominator each time */
314                         int denom = dp->dccps_l_ack_ratio * dp->dccps_l_ack_ratio -
315                                     dp->dccps_l_ack_ratio;
316 
317                         denom = hc->tx_cwnd * hc->tx_cwnd / denom;
318 
319                         if (hc->tx_arsent >= denom) {
320                                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
321                                 hc->tx_arsent = 0;
322                         }
323                 } else {
324                         /* we can't increase ack ratio further [1] */
325                         hc->tx_arsent = 0; /* or maybe set it to cwnd*/
326                 }
327         }
328 #endif
329 
330         sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
331 
332 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
333         do {
334                 struct ccid2_seq *seqp = hc->tx_seqt;
335 
336                 while (seqp != hc->tx_seqh) {
337                         ccid2_pr_debug("out seq=%llu acked=%d time=%u\n",
338                                        (unsigned long long)seqp->ccid2s_seq,
339                                        seqp->ccid2s_acked, seqp->ccid2s_sent);
340                         seqp = seqp->ccid2s_next;
341                 }
342         } while (0);
343         ccid2_pr_debug("=========\n");
344 #endif
345 }
346 
347 /**
348  * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
349  * This code is almost identical with TCP's tcp_rtt_estimator(), since
350  * - it has a higher sampling frequency (recommended by RFC 1323),
351  * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
352  * - it is simple (cf. more complex proposals such as Eifel timer or research
353  *   which suggests that the gain should be set according to window size),
354  * - in tests it was found to work well with CCID2 [gerrit].
355  */
356 static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
357 {
358         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
359         long m = mrtt ? : 1;
360 
361         if (hc->tx_srtt == 0) {
362                 /* First measurement m */
363                 hc->tx_srtt = m << 3;
364                 hc->tx_mdev = m << 1;
365 
366                 hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
367                 hc->tx_rttvar   = hc->tx_mdev_max;
368 
369                 hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
370         } else {
371                 /* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
372                 m -= (hc->tx_srtt >> 3);
373                 hc->tx_srtt += m;
374 
375                 /* Similarly, update scaled mdev with regard to |m| */
376                 if (m < 0) {
377                         m = -m;
378                         m -= (hc->tx_mdev >> 2);
379                         /*
380                          * This neutralises RTO increase when RTT < SRTT - mdev
381                          * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
382                          * in Linux TCP", USENIX 2002, pp. 49-62).
383                          */
384                         if (m > 0)
385                                 m >>= 3;
386                 } else {
387                         m -= (hc->tx_mdev >> 2);
388                 }
389                 hc->tx_mdev += m;
390 
391                 if (hc->tx_mdev > hc->tx_mdev_max) {
392                         hc->tx_mdev_max = hc->tx_mdev;
393                         if (hc->tx_mdev_max > hc->tx_rttvar)
394                                 hc->tx_rttvar = hc->tx_mdev_max;
395                 }
396 
397                 /*
398                  * Decay RTTVAR at most once per flight, exploiting that
399                  *  1) pipe <= cwnd <= Sequence_Window = W  (RFC 4340, 7.5.2)
400                  *  2) AWL = GSS-W+1 <= GAR <= GSS          (RFC 4340, 7.5.1)
401                  * GAR is a useful bound for FlightSize = pipe.
402                  * AWL is probably too low here, as it over-estimates pipe.
403                  */
404                 if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
405                         if (hc->tx_mdev_max < hc->tx_rttvar)
406                                 hc->tx_rttvar -= (hc->tx_rttvar -
407                                                   hc->tx_mdev_max) >> 2;
408                         hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
409                         hc->tx_mdev_max = tcp_rto_min(sk);
410                 }
411         }
412 
413         /*
414          * Set RTO from SRTT and RTTVAR
415          * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
416          * This agrees with RFC 4341, 5:
417          *      "Because DCCP does not retransmit data, DCCP does not require
418          *       TCP's recommended minimum timeout of one second".
419          */
420         hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;
421 
422         if (hc->tx_rto > DCCP_RTO_MAX)
423                 hc->tx_rto = DCCP_RTO_MAX;
424 }
425 
426 static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
427                           unsigned int *maxincr)
428 {
429         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
430         struct dccp_sock *dp = dccp_sk(sk);
431         int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;
432 
433         if (hc->tx_cwnd < dp->dccps_l_seq_win &&
434             r_seq_used < dp->dccps_r_seq_win) {
435                 if (hc->tx_cwnd < hc->tx_ssthresh) {
436                         if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) {
437                                 hc->tx_cwnd += 1;
438                                 *maxincr    -= 1;
439                                 hc->tx_packets_acked = 0;
440                         }
441                 } else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
442                         hc->tx_cwnd += 1;
443                         hc->tx_packets_acked = 0;
444                 }
445         }
446 
447         /*
448          * Adjust the local sequence window and the ack ratio to allow about
449          * 5 times the number of packets in the network (RFC 4340 7.5.2)
450          */
451         if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
452                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2);
453         else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2)
454                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U);
455 
456         if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
457                 ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2);
458         else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2)
459                 ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2);
460 
461         /*
462          * FIXME: RTT is sampled several times per acknowledgment (for each
463          * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
464          * This causes the RTT to be over-estimated, since the older entries
465          * in the Ack Vector have earlier sending times.
466          * The cleanest solution is to not use the ccid2s_sent field at all
467          * and instead use DCCP timestamps: requires changes in other places.
468          */
469         ccid2_rtt_estimator(sk, ccid2_time_stamp - seqp->ccid2s_sent);
470 }
471 
472 static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
473 {
474         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
475 
476         if ((s32)(seqp->ccid2s_sent - hc->tx_last_cong) < 0) {
477                 ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
478                 return;
479         }
480 
481         hc->tx_last_cong = ccid2_time_stamp;
482 
483         hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
484         hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);
485 
486         ccid2_check_l_ack_ratio(sk);
487 }
488 
489 static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
490                                      u8 option, u8 *optval, u8 optlen)
491 {
492         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
493 
494         switch (option) {
495         case DCCPO_ACK_VECTOR_0:
496         case DCCPO_ACK_VECTOR_1:
497                 return dccp_ackvec_parsed_add(&hc->tx_av_chunks, optval, optlen,
498                                               option - DCCPO_ACK_VECTOR_0);
499         }
500         return 0;
501 }
502 
503 static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
504 {
505         struct dccp_sock *dp = dccp_sk(sk);
506         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
507         const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
508         struct dccp_ackvec_parsed *avp;
509         u64 ackno, seqno;
510         struct ccid2_seq *seqp;
511         int done = 0;
512         unsigned int maxincr = 0;
513 
514         /* check reverse path congestion */
515         seqno = DCCP_SKB_CB(skb)->dccpd_seq;
516 
517         /* XXX this whole "algorithm" is broken.  Need to fix it to keep track
518          * of the seqnos of the dupacks so that rpseq and rpdupack are correct
519          * -sorbo.
520          */
521         /* need to bootstrap */
522         if (hc->tx_rpdupack == -1) {
523                 hc->tx_rpdupack = 0;
524                 hc->tx_rpseq    = seqno;
525         } else {
526                 /* check if packet is consecutive */
527                 if (dccp_delta_seqno(hc->tx_rpseq, seqno) == 1)
528                         hc->tx_rpseq = seqno;
529                 /* it's a later packet */
530                 else if (after48(seqno, hc->tx_rpseq)) {
531                         hc->tx_rpdupack++;
532 
533                         /* check if we got enough dupacks */
534                         if (hc->tx_rpdupack >= NUMDUPACK) {
535                                 hc->tx_rpdupack = -1; /* XXX lame */
536                                 hc->tx_rpseq    = 0;
537 #ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
538                                 /*
539                                  * FIXME: Ack Congestion Control is broken; in
540                                  * the current state instabilities occurred with
541                                  * Ack Ratios greater than 1; causing hang-ups
542                                  * and long RTO timeouts. This needs to be fixed
543                                  * before opening up dynamic changes. -- gerrit
544                                  */
545                                 ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
546 #endif
547                         }
548                 }
549         }
550 
551         /* check forward path congestion */
552         if (dccp_packet_without_ack(skb))
553                 return;
554 
555         /* still didn't send out new data packets */
556         if (hc->tx_seqh == hc->tx_seqt)
557                 goto done;
558 
559         ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
560         if (after48(ackno, hc->tx_high_ack))
561                 hc->tx_high_ack = ackno;
562 
563         seqp = hc->tx_seqt;
564         while (before48(seqp->ccid2s_seq, ackno)) {
565                 seqp = seqp->ccid2s_next;
566                 if (seqp == hc->tx_seqh) {
567                         seqp = hc->tx_seqh->ccid2s_prev;
568                         break;
569                 }
570         }
571 
572         /*
573          * In slow-start, cwnd can increase up to a maximum of Ack Ratio/2
574          * packets per acknowledgement. Rounding up avoids that cwnd is not
575          * advanced when Ack Ratio is 1 and gives a slight edge otherwise.
576          */
577         if (hc->tx_cwnd < hc->tx_ssthresh)
578                 maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);
579 
580         /* go through all ack vectors */
581         list_for_each_entry(avp, &hc->tx_av_chunks, node) {
582                 /* go through this ack vector */
583                 for (; avp->len--; avp->vec++) {
584                         u64 ackno_end_rl = SUB48(ackno,
585                                                  dccp_ackvec_runlen(avp->vec));
586 
587                         ccid2_pr_debug("ackvec %llu |%u,%u|\n",
588                                        (unsigned long long)ackno,
589                                        dccp_ackvec_state(avp->vec) >> 6,
590                                        dccp_ackvec_runlen(avp->vec));
591                         /* if the seqno we are analyzing is larger than the
592                          * current ackno, then move towards the tail of our
593                          * seqnos.
594                          */
595                         while (after48(seqp->ccid2s_seq, ackno)) {
596                                 if (seqp == hc->tx_seqt) {
597                                         done = 1;
598                                         break;
599                                 }
600                                 seqp = seqp->ccid2s_prev;
601                         }
602                         if (done)
603                                 break;
604 
605                         /* check all seqnos in the range of the vector
606                          * run length
607                          */
608                         while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
609                                 const u8 state = dccp_ackvec_state(avp->vec);
610 
611                                 /* new packet received or marked */
612                                 if (state != DCCPAV_NOT_RECEIVED &&
613                                     !seqp->ccid2s_acked) {
614                                         if (state == DCCPAV_ECN_MARKED)
615                                                 ccid2_congestion_event(sk,
616                                                                        seqp);
617                                         else
618                                                 ccid2_new_ack(sk, seqp,
619                                                               &maxincr);
620 
621                                         seqp->ccid2s_acked = 1;
622                                         ccid2_pr_debug("Got ack for %llu\n",
623                                                        (unsigned long long)seqp->ccid2s_seq);
624                                         hc->tx_pipe--;
625                                 }
626                                 if (seqp == hc->tx_seqt) {
627                                         done = 1;
628                                         break;
629                                 }
630                                 seqp = seqp->ccid2s_prev;
631                         }
632                         if (done)
633                                 break;
634 
635                         ackno = SUB48(ackno_end_rl, 1);
636                 }
637                 if (done)
638                         break;
639         }
640 
641         /* The state about what is acked should be correct now
642          * Check for NUMDUPACK
643          */
644         seqp = hc->tx_seqt;
645         while (before48(seqp->ccid2s_seq, hc->tx_high_ack)) {
646                 seqp = seqp->ccid2s_next;
647                 if (seqp == hc->tx_seqh) {
648                         seqp = hc->tx_seqh->ccid2s_prev;
649                         break;
650                 }
651         }
652         done = 0;
653         while (1) {
654                 if (seqp->ccid2s_acked) {
655                         done++;
656                         if (done == NUMDUPACK)
657                                 break;
658                 }
659                 if (seqp == hc->tx_seqt)
660                         break;
661                 seqp = seqp->ccid2s_prev;
662         }
663 
664         /* If there are at least 3 acknowledgements, anything unacknowledged
665          * below the last sequence number is considered lost
666          */
667         if (done == NUMDUPACK) {
668                 struct ccid2_seq *last_acked = seqp;
669 
670                 /* check for lost packets */
671                 while (1) {
672                         if (!seqp->ccid2s_acked) {
673                                 ccid2_pr_debug("Packet lost: %llu\n",
674                                                (unsigned long long)seqp->ccid2s_seq);
675                                 /* XXX need to traverse from tail -> head in
676                                  * order to detect multiple congestion events in
677                                  * one ack vector.
678                                  */
679                                 ccid2_congestion_event(sk, seqp);
680                                 hc->tx_pipe--;
681                         }
682                         if (seqp == hc->tx_seqt)
683                                 break;
684                         seqp = seqp->ccid2s_prev;
685                 }
686 
687                 hc->tx_seqt = last_acked;
688         }
689 
690         /* trim acked packets in tail */
691         while (hc->tx_seqt != hc->tx_seqh) {
692                 if (!hc->tx_seqt->ccid2s_acked)
693                         break;
694 
695                 hc->tx_seqt = hc->tx_seqt->ccid2s_next;
696         }
697 
698         /* restart RTO timer if not all outstanding data has been acked */
699         if (hc->tx_pipe == 0)
700                 sk_stop_timer(sk, &hc->tx_rtotimer);
701         else
702                 sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
703 done:
704         /* check if incoming Acks allow pending packets to be sent */
705         if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
706                 tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
707         dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
708 }
709 
710 static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
711 {
712         struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
713         struct dccp_sock *dp = dccp_sk(sk);
714         u32 max_ratio;
715 
716         /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
717         hc->tx_ssthresh = ~0U;
718 
719         /* Use larger initial windows (RFC 4341, section 5). */
720         hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
721         hc->tx_expected_wnd = hc->tx_cwnd;
722 
723         /* Make sure that Ack Ratio is enabled and within bounds. */
724         max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
725         if (dp->dccps_l_ack_ratio == 0 || dp->dccps_l_ack_ratio > max_ratio)
726                 dp->dccps_l_ack_ratio = max_ratio;
727 
728         /* XXX init ~ to window size... */
729         if (ccid2_hc_tx_alloc_seq(hc))
730                 return -ENOMEM;
731 
732         hc->tx_rto       = DCCP_TIMEOUT_INIT;
733         hc->tx_rpdupack  = -1;
734         hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_time_stamp;
735         hc->tx_cwnd_used = 0;
736         setup_timer(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire,
737                         (unsigned long)sk);
738         INIT_LIST_HEAD(&hc->tx_av_chunks);
739         return 0;
740 }
741 
742 static void ccid2_hc_tx_exit(struct sock *sk)
743 {
744         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
745         int i;
746 
747         sk_stop_timer(sk, &hc->tx_rtotimer);
748 
749         for (i = 0; i < hc->tx_seqbufc; i++)
750                 kfree(hc->tx_seqbuf[i]);
751         hc->tx_seqbufc = 0;
752         dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
753 }
754 
755 static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
756 {
757         struct ccid2_hc_rx_sock *hc = ccid2_hc_rx_sk(sk);
758 
759         if (!dccp_data_packet(skb))
760                 return;
761 
762         if (++hc->rx_num_data_pkts >= dccp_sk(sk)->dccps_r_ack_ratio) {
763                 dccp_send_ack(sk);
764                 hc->rx_num_data_pkts = 0;
765         }
766 }
767 
768 struct ccid_operations ccid2_ops = {
769         .ccid_id                  = DCCPC_CCID2,
770         .ccid_name                = "TCP-like",
771         .ccid_hc_tx_obj_size      = sizeof(struct ccid2_hc_tx_sock),
772         .ccid_hc_tx_init          = ccid2_hc_tx_init,
773         .ccid_hc_tx_exit          = ccid2_hc_tx_exit,
774         .ccid_hc_tx_send_packet   = ccid2_hc_tx_send_packet,
775         .ccid_hc_tx_packet_sent   = ccid2_hc_tx_packet_sent,
776         .ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
777         .ccid_hc_tx_packet_recv   = ccid2_hc_tx_packet_recv,
778         .ccid_hc_rx_obj_size      = sizeof(struct ccid2_hc_rx_sock),
779         .ccid_hc_rx_packet_recv   = ccid2_hc_rx_packet_recv,
780 };
781 
782 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
783 module_param(ccid2_debug, bool, 0644);
784 MODULE_PARM_DESC(ccid2_debug, "Enable CCID-2 debug messages");
785 #endif
786 

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