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Linux/net/dccp/ccids/ccid2.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  *  Copyright (c) 2005, 2006 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
  4  *
  5  *  Changes to meet Linux coding standards, and DCCP infrastructure fixes.
  6  *
  7  *  Copyright (c) 2006 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  8  */
  9 
 10 /*
 11  * This implementation should follow RFC 4341
 12  */
 13 #include <linux/slab.h>
 14 #include "../feat.h"
 15 #include "ccid2.h"
 16 
 17 
 18 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
 19 static bool ccid2_debug;
 20 #define ccid2_pr_debug(format, a...)    DCCP_PR_DEBUG(ccid2_debug, format, ##a)
 21 #else
 22 #define ccid2_pr_debug(format, a...)
 23 #endif
 24 
 25 static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hc)
 26 {
 27         struct ccid2_seq *seqp;
 28         int i;
 29 
 30         /* check if we have space to preserve the pointer to the buffer */
 31         if (hc->tx_seqbufc >= (sizeof(hc->tx_seqbuf) /
 32                                sizeof(struct ccid2_seq *)))
 33                 return -ENOMEM;
 34 
 35         /* allocate buffer and initialize linked list */
 36         seqp = kmalloc_array(CCID2_SEQBUF_LEN, sizeof(struct ccid2_seq),
 37                              gfp_any());
 38         if (seqp == NULL)
 39                 return -ENOMEM;
 40 
 41         for (i = 0; i < (CCID2_SEQBUF_LEN - 1); i++) {
 42                 seqp[i].ccid2s_next = &seqp[i + 1];
 43                 seqp[i + 1].ccid2s_prev = &seqp[i];
 44         }
 45         seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = seqp;
 46         seqp->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
 47 
 48         /* This is the first allocation.  Initiate the head and tail.  */
 49         if (hc->tx_seqbufc == 0)
 50                 hc->tx_seqh = hc->tx_seqt = seqp;
 51         else {
 52                 /* link the existing list with the one we just created */
 53                 hc->tx_seqh->ccid2s_next = seqp;
 54                 seqp->ccid2s_prev = hc->tx_seqh;
 55 
 56                 hc->tx_seqt->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
 57                 seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = hc->tx_seqt;
 58         }
 59 
 60         /* store the original pointer to the buffer so we can free it */
 61         hc->tx_seqbuf[hc->tx_seqbufc] = seqp;
 62         hc->tx_seqbufc++;
 63 
 64         return 0;
 65 }
 66 
 67 static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 68 {
 69         if (ccid2_cwnd_network_limited(ccid2_hc_tx_sk(sk)))
 70                 return CCID_PACKET_WILL_DEQUEUE_LATER;
 71         return CCID_PACKET_SEND_AT_ONCE;
 72 }
 73 
 74 static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
 75 {
 76         u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);
 77 
 78         /*
 79          * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
 80          * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
 81          * acceptable since this causes starvation/deadlock whenever cwnd < 2.
 82          * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
 83          */
 84         if (val == 0 || val > max_ratio) {
 85                 DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
 86                 val = max_ratio;
 87         }
 88         dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
 89                                    min_t(u32, val, DCCPF_ACK_RATIO_MAX));
 90 }
 91 
 92 static void ccid2_check_l_ack_ratio(struct sock *sk)
 93 {
 94         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
 95 
 96         /*
 97          * After a loss, idle period, application limited period, or RTO we
 98          * need to check that the ack ratio is still less than the congestion
 99          * window. Otherwise, we will send an entire congestion window of
100          * packets and got no response because we haven't sent ack ratio
101          * packets yet.
102          * If the ack ratio does need to be reduced, we reduce it to half of
103          * the congestion window (or 1 if that's zero) instead of to the
104          * congestion window. This prevents problems if one ack is lost.
105          */
106         if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
107                 ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
108 }
109 
110 static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
111 {
112         dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
113                                    clamp_val(val, DCCPF_SEQ_WMIN,
114                                                   DCCPF_SEQ_WMAX));
115 }
116 
117 static void dccp_tasklet_schedule(struct sock *sk)
118 {
119         struct tasklet_struct *t = &dccp_sk(sk)->dccps_xmitlet;
120 
121         if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
122                 sock_hold(sk);
123                 __tasklet_schedule(t);
124         }
125 }
126 
127 static void ccid2_hc_tx_rto_expire(struct timer_list *t)
128 {
129         struct ccid2_hc_tx_sock *hc = from_timer(hc, t, tx_rtotimer);
130         struct sock *sk = hc->sk;
131         const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
132 
133         bh_lock_sock(sk);
134         if (sock_owned_by_user(sk)) {
135                 sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
136                 goto out;
137         }
138 
139         ccid2_pr_debug("RTO_EXPIRE\n");
140 
141         if (sk->sk_state == DCCP_CLOSED)
142                 goto out;
143 
144         /* back-off timer */
145         hc->tx_rto <<= 1;
146         if (hc->tx_rto > DCCP_RTO_MAX)
147                 hc->tx_rto = DCCP_RTO_MAX;
148 
149         /* adjust pipe, cwnd etc */
150         hc->tx_ssthresh = hc->tx_cwnd / 2;
151         if (hc->tx_ssthresh < 2)
152                 hc->tx_ssthresh = 2;
153         hc->tx_cwnd     = 1;
154         hc->tx_pipe     = 0;
155 
156         /* clear state about stuff we sent */
157         hc->tx_seqt = hc->tx_seqh;
158         hc->tx_packets_acked = 0;
159 
160         /* clear ack ratio state. */
161         hc->tx_rpseq    = 0;
162         hc->tx_rpdupack = -1;
163         ccid2_change_l_ack_ratio(sk, 1);
164 
165         /* if we were blocked before, we may now send cwnd=1 packet */
166         if (sender_was_blocked)
167                 dccp_tasklet_schedule(sk);
168         /* restart backed-off timer */
169         sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
170 out:
171         bh_unlock_sock(sk);
172         sock_put(sk);
173 }
174 
175 /*
176  *      Congestion window validation (RFC 2861).
177  */
178 static bool ccid2_do_cwv = true;
179 module_param(ccid2_do_cwv, bool, 0644);
180 MODULE_PARM_DESC(ccid2_do_cwv, "Perform RFC2861 Congestion Window Validation");
181 
182 /**
183  * ccid2_update_used_window  -  Track how much of cwnd is actually used
184  * @hc: socket to update window
185  * @new_wnd: new window values to add into the filter
186  *
187  * This is done in addition to CWV. The sender needs to have an idea of how many
188  * packets may be in flight, to set the local Sequence Window value accordingly
189  * (RFC 4340, 7.5.2). The CWV mechanism is exploited to keep track of the
190  * maximum-used window. We use an EWMA low-pass filter to filter out noise.
191  */
192 static void ccid2_update_used_window(struct ccid2_hc_tx_sock *hc, u32 new_wnd)
193 {
194         hc->tx_expected_wnd = (3 * hc->tx_expected_wnd + new_wnd) / 4;
195 }
196 
197 /* This borrows the code of tcp_cwnd_application_limited() */
198 static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
199 {
200         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
201         /* don't reduce cwnd below the initial window (IW) */
202         u32 init_win = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache),
203             win_used = max(hc->tx_cwnd_used, init_win);
204 
205         if (win_used < hc->tx_cwnd) {
206                 hc->tx_ssthresh = max(hc->tx_ssthresh,
207                                      (hc->tx_cwnd >> 1) + (hc->tx_cwnd >> 2));
208                 hc->tx_cwnd = (hc->tx_cwnd + win_used) >> 1;
209         }
210         hc->tx_cwnd_used  = 0;
211         hc->tx_cwnd_stamp = now;
212 
213         ccid2_check_l_ack_ratio(sk);
214 }
215 
216 /* This borrows the code of tcp_cwnd_restart() */
217 static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
218 {
219         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
220         u32 cwnd = hc->tx_cwnd, restart_cwnd,
221             iwnd = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache);
222         s32 delta = now - hc->tx_lsndtime;
223 
224         hc->tx_ssthresh = max(hc->tx_ssthresh, (cwnd >> 1) + (cwnd >> 2));
225 
226         /* don't reduce cwnd below the initial window (IW) */
227         restart_cwnd = min(cwnd, iwnd);
228 
229         while ((delta -= hc->tx_rto) >= 0 && cwnd > restart_cwnd)
230                 cwnd >>= 1;
231         hc->tx_cwnd = max(cwnd, restart_cwnd);
232         hc->tx_cwnd_stamp = now;
233         hc->tx_cwnd_used  = 0;
234 
235         ccid2_check_l_ack_ratio(sk);
236 }
237 
238 static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
239 {
240         struct dccp_sock *dp = dccp_sk(sk);
241         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
242         const u32 now = ccid2_jiffies32;
243         struct ccid2_seq *next;
244 
245         /* slow-start after idle periods (RFC 2581, RFC 2861) */
246         if (ccid2_do_cwv && !hc->tx_pipe &&
247             (s32)(now - hc->tx_lsndtime) >= hc->tx_rto)
248                 ccid2_cwnd_restart(sk, now);
249 
250         hc->tx_lsndtime = now;
251         hc->tx_pipe    += 1;
252 
253         /* see whether cwnd was fully used (RFC 2861), update expected window */
254         if (ccid2_cwnd_network_limited(hc)) {
255                 ccid2_update_used_window(hc, hc->tx_cwnd);
256                 hc->tx_cwnd_used  = 0;
257                 hc->tx_cwnd_stamp = now;
258         } else {
259                 if (hc->tx_pipe > hc->tx_cwnd_used)
260                         hc->tx_cwnd_used = hc->tx_pipe;
261 
262                 ccid2_update_used_window(hc, hc->tx_cwnd_used);
263 
264                 if (ccid2_do_cwv && (s32)(now - hc->tx_cwnd_stamp) >= hc->tx_rto)
265                         ccid2_cwnd_application_limited(sk, now);
266         }
267 
268         hc->tx_seqh->ccid2s_seq   = dp->dccps_gss;
269         hc->tx_seqh->ccid2s_acked = 0;
270         hc->tx_seqh->ccid2s_sent  = now;
271 
272         next = hc->tx_seqh->ccid2s_next;
273         /* check if we need to alloc more space */
274         if (next == hc->tx_seqt) {
275                 if (ccid2_hc_tx_alloc_seq(hc)) {
276                         DCCP_CRIT("packet history - out of memory!");
277                         /* FIXME: find a more graceful way to bail out */
278                         return;
279                 }
280                 next = hc->tx_seqh->ccid2s_next;
281                 BUG_ON(next == hc->tx_seqt);
282         }
283         hc->tx_seqh = next;
284 
285         ccid2_pr_debug("cwnd=%d pipe=%d\n", hc->tx_cwnd, hc->tx_pipe);
286 
287         /*
288          * FIXME: The code below is broken and the variables have been removed
289          * from the socket struct. The `ackloss' variable was always set to 0,
290          * and with arsent there are several problems:
291          *  (i) it doesn't just count the number of Acks, but all sent packets;
292          *  (ii) it is expressed in # of packets, not # of windows, so the
293          *  comparison below uses the wrong formula: Appendix A of RFC 4341
294          *  comes up with the number K = cwnd / (R^2 - R) of consecutive windows
295          *  of data with no lost or marked Ack packets. If arsent were the # of
296          *  consecutive Acks received without loss, then Ack Ratio needs to be
297          *  decreased by 1 when
298          *            arsent >=  K * cwnd / R  =  cwnd^2 / (R^3 - R^2)
299          *  where cwnd / R is the number of Acks received per window of data
300          *  (cf. RFC 4341, App. A). The problems are that
301          *  - arsent counts other packets as well;
302          *  - the comparison uses a formula different from RFC 4341;
303          *  - computing a cubic/quadratic equation each time is too complicated.
304          *  Hence a different algorithm is needed.
305          */
306 #if 0
307         /* Ack Ratio.  Need to maintain a concept of how many windows we sent */
308         hc->tx_arsent++;
309         /* We had an ack loss in this window... */
310         if (hc->tx_ackloss) {
311                 if (hc->tx_arsent >= hc->tx_cwnd) {
312                         hc->tx_arsent  = 0;
313                         hc->tx_ackloss = 0;
314                 }
315         } else {
316                 /* No acks lost up to now... */
317                 /* decrease ack ratio if enough packets were sent */
318                 if (dp->dccps_l_ack_ratio > 1) {
319                         /* XXX don't calculate denominator each time */
320                         int denom = dp->dccps_l_ack_ratio * dp->dccps_l_ack_ratio -
321                                     dp->dccps_l_ack_ratio;
322 
323                         denom = hc->tx_cwnd * hc->tx_cwnd / denom;
324 
325                         if (hc->tx_arsent >= denom) {
326                                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
327                                 hc->tx_arsent = 0;
328                         }
329                 } else {
330                         /* we can't increase ack ratio further [1] */
331                         hc->tx_arsent = 0; /* or maybe set it to cwnd*/
332                 }
333         }
334 #endif
335 
336         sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
337 
338 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
339         do {
340                 struct ccid2_seq *seqp = hc->tx_seqt;
341 
342                 while (seqp != hc->tx_seqh) {
343                         ccid2_pr_debug("out seq=%llu acked=%d time=%u\n",
344                                        (unsigned long long)seqp->ccid2s_seq,
345                                        seqp->ccid2s_acked, seqp->ccid2s_sent);
346                         seqp = seqp->ccid2s_next;
347                 }
348         } while (0);
349         ccid2_pr_debug("=========\n");
350 #endif
351 }
352 
353 /**
354  * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
355  * @sk: socket to perform estimator on
356  * @mrtt: measured RTT
357  *
358  * This code is almost identical with TCP's tcp_rtt_estimator(), since
359  * - it has a higher sampling frequency (recommended by RFC 1323),
360  * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
361  * - it is simple (cf. more complex proposals such as Eifel timer or research
362  *   which suggests that the gain should be set according to window size),
363  * - in tests it was found to work well with CCID2 [gerrit].
364  */
365 static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
366 {
367         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
368         long m = mrtt ? : 1;
369 
370         if (hc->tx_srtt == 0) {
371                 /* First measurement m */
372                 hc->tx_srtt = m << 3;
373                 hc->tx_mdev = m << 1;
374 
375                 hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
376                 hc->tx_rttvar   = hc->tx_mdev_max;
377 
378                 hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
379         } else {
380                 /* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
381                 m -= (hc->tx_srtt >> 3);
382                 hc->tx_srtt += m;
383 
384                 /* Similarly, update scaled mdev with regard to |m| */
385                 if (m < 0) {
386                         m = -m;
387                         m -= (hc->tx_mdev >> 2);
388                         /*
389                          * This neutralises RTO increase when RTT < SRTT - mdev
390                          * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
391                          * in Linux TCP", USENIX 2002, pp. 49-62).
392                          */
393                         if (m > 0)
394                                 m >>= 3;
395                 } else {
396                         m -= (hc->tx_mdev >> 2);
397                 }
398                 hc->tx_mdev += m;
399 
400                 if (hc->tx_mdev > hc->tx_mdev_max) {
401                         hc->tx_mdev_max = hc->tx_mdev;
402                         if (hc->tx_mdev_max > hc->tx_rttvar)
403                                 hc->tx_rttvar = hc->tx_mdev_max;
404                 }
405 
406                 /*
407                  * Decay RTTVAR at most once per flight, exploiting that
408                  *  1) pipe <= cwnd <= Sequence_Window = W  (RFC 4340, 7.5.2)
409                  *  2) AWL = GSS-W+1 <= GAR <= GSS          (RFC 4340, 7.5.1)
410                  * GAR is a useful bound for FlightSize = pipe.
411                  * AWL is probably too low here, as it over-estimates pipe.
412                  */
413                 if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
414                         if (hc->tx_mdev_max < hc->tx_rttvar)
415                                 hc->tx_rttvar -= (hc->tx_rttvar -
416                                                   hc->tx_mdev_max) >> 2;
417                         hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
418                         hc->tx_mdev_max = tcp_rto_min(sk);
419                 }
420         }
421 
422         /*
423          * Set RTO from SRTT and RTTVAR
424          * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
425          * This agrees with RFC 4341, 5:
426          *      "Because DCCP does not retransmit data, DCCP does not require
427          *       TCP's recommended minimum timeout of one second".
428          */
429         hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;
430 
431         if (hc->tx_rto > DCCP_RTO_MAX)
432                 hc->tx_rto = DCCP_RTO_MAX;
433 }
434 
435 static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
436                           unsigned int *maxincr)
437 {
438         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
439         struct dccp_sock *dp = dccp_sk(sk);
440         int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;
441 
442         if (hc->tx_cwnd < dp->dccps_l_seq_win &&
443             r_seq_used < dp->dccps_r_seq_win) {
444                 if (hc->tx_cwnd < hc->tx_ssthresh) {
445                         if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) {
446                                 hc->tx_cwnd += 1;
447                                 *maxincr    -= 1;
448                                 hc->tx_packets_acked = 0;
449                         }
450                 } else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
451                         hc->tx_cwnd += 1;
452                         hc->tx_packets_acked = 0;
453                 }
454         }
455 
456         /*
457          * Adjust the local sequence window and the ack ratio to allow about
458          * 5 times the number of packets in the network (RFC 4340 7.5.2)
459          */
460         if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
461                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2);
462         else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2)
463                 ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U);
464 
465         if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
466                 ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2);
467         else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2)
468                 ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2);
469 
470         /*
471          * FIXME: RTT is sampled several times per acknowledgment (for each
472          * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
473          * This causes the RTT to be over-estimated, since the older entries
474          * in the Ack Vector have earlier sending times.
475          * The cleanest solution is to not use the ccid2s_sent field at all
476          * and instead use DCCP timestamps: requires changes in other places.
477          */
478         ccid2_rtt_estimator(sk, ccid2_jiffies32 - seqp->ccid2s_sent);
479 }
480 
481 static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
482 {
483         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
484 
485         if ((s32)(seqp->ccid2s_sent - hc->tx_last_cong) < 0) {
486                 ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
487                 return;
488         }
489 
490         hc->tx_last_cong = ccid2_jiffies32;
491 
492         hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
493         hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);
494 
495         ccid2_check_l_ack_ratio(sk);
496 }
497 
498 static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
499                                      u8 option, u8 *optval, u8 optlen)
500 {
501         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
502 
503         switch (option) {
504         case DCCPO_ACK_VECTOR_0:
505         case DCCPO_ACK_VECTOR_1:
506                 return dccp_ackvec_parsed_add(&hc->tx_av_chunks, optval, optlen,
507                                               option - DCCPO_ACK_VECTOR_0);
508         }
509         return 0;
510 }
511 
512 static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
513 {
514         struct dccp_sock *dp = dccp_sk(sk);
515         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
516         const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
517         struct dccp_ackvec_parsed *avp;
518         u64 ackno, seqno;
519         struct ccid2_seq *seqp;
520         int done = 0;
521         unsigned int maxincr = 0;
522 
523         /* check reverse path congestion */
524         seqno = DCCP_SKB_CB(skb)->dccpd_seq;
525 
526         /* XXX this whole "algorithm" is broken.  Need to fix it to keep track
527          * of the seqnos of the dupacks so that rpseq and rpdupack are correct
528          * -sorbo.
529          */
530         /* need to bootstrap */
531         if (hc->tx_rpdupack == -1) {
532                 hc->tx_rpdupack = 0;
533                 hc->tx_rpseq    = seqno;
534         } else {
535                 /* check if packet is consecutive */
536                 if (dccp_delta_seqno(hc->tx_rpseq, seqno) == 1)
537                         hc->tx_rpseq = seqno;
538                 /* it's a later packet */
539                 else if (after48(seqno, hc->tx_rpseq)) {
540                         hc->tx_rpdupack++;
541 
542                         /* check if we got enough dupacks */
543                         if (hc->tx_rpdupack >= NUMDUPACK) {
544                                 hc->tx_rpdupack = -1; /* XXX lame */
545                                 hc->tx_rpseq    = 0;
546 #ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
547                                 /*
548                                  * FIXME: Ack Congestion Control is broken; in
549                                  * the current state instabilities occurred with
550                                  * Ack Ratios greater than 1; causing hang-ups
551                                  * and long RTO timeouts. This needs to be fixed
552                                  * before opening up dynamic changes. -- gerrit
553                                  */
554                                 ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
555 #endif
556                         }
557                 }
558         }
559 
560         /* check forward path congestion */
561         if (dccp_packet_without_ack(skb))
562                 return;
563 
564         /* still didn't send out new data packets */
565         if (hc->tx_seqh == hc->tx_seqt)
566                 goto done;
567 
568         ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
569         if (after48(ackno, hc->tx_high_ack))
570                 hc->tx_high_ack = ackno;
571 
572         seqp = hc->tx_seqt;
573         while (before48(seqp->ccid2s_seq, ackno)) {
574                 seqp = seqp->ccid2s_next;
575                 if (seqp == hc->tx_seqh) {
576                         seqp = hc->tx_seqh->ccid2s_prev;
577                         break;
578                 }
579         }
580 
581         /*
582          * In slow-start, cwnd can increase up to a maximum of Ack Ratio/2
583          * packets per acknowledgement. Rounding up avoids that cwnd is not
584          * advanced when Ack Ratio is 1 and gives a slight edge otherwise.
585          */
586         if (hc->tx_cwnd < hc->tx_ssthresh)
587                 maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);
588 
589         /* go through all ack vectors */
590         list_for_each_entry(avp, &hc->tx_av_chunks, node) {
591                 /* go through this ack vector */
592                 for (; avp->len--; avp->vec++) {
593                         u64 ackno_end_rl = SUB48(ackno,
594                                                  dccp_ackvec_runlen(avp->vec));
595 
596                         ccid2_pr_debug("ackvec %llu |%u,%u|\n",
597                                        (unsigned long long)ackno,
598                                        dccp_ackvec_state(avp->vec) >> 6,
599                                        dccp_ackvec_runlen(avp->vec));
600                         /* if the seqno we are analyzing is larger than the
601                          * current ackno, then move towards the tail of our
602                          * seqnos.
603                          */
604                         while (after48(seqp->ccid2s_seq, ackno)) {
605                                 if (seqp == hc->tx_seqt) {
606                                         done = 1;
607                                         break;
608                                 }
609                                 seqp = seqp->ccid2s_prev;
610                         }
611                         if (done)
612                                 break;
613 
614                         /* check all seqnos in the range of the vector
615                          * run length
616                          */
617                         while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
618                                 const u8 state = dccp_ackvec_state(avp->vec);
619 
620                                 /* new packet received or marked */
621                                 if (state != DCCPAV_NOT_RECEIVED &&
622                                     !seqp->ccid2s_acked) {
623                                         if (state == DCCPAV_ECN_MARKED)
624                                                 ccid2_congestion_event(sk,
625                                                                        seqp);
626                                         else
627                                                 ccid2_new_ack(sk, seqp,
628                                                               &maxincr);
629 
630                                         seqp->ccid2s_acked = 1;
631                                         ccid2_pr_debug("Got ack for %llu\n",
632                                                        (unsigned long long)seqp->ccid2s_seq);
633                                         hc->tx_pipe--;
634                                 }
635                                 if (seqp == hc->tx_seqt) {
636                                         done = 1;
637                                         break;
638                                 }
639                                 seqp = seqp->ccid2s_prev;
640                         }
641                         if (done)
642                                 break;
643 
644                         ackno = SUB48(ackno_end_rl, 1);
645                 }
646                 if (done)
647                         break;
648         }
649 
650         /* The state about what is acked should be correct now
651          * Check for NUMDUPACK
652          */
653         seqp = hc->tx_seqt;
654         while (before48(seqp->ccid2s_seq, hc->tx_high_ack)) {
655                 seqp = seqp->ccid2s_next;
656                 if (seqp == hc->tx_seqh) {
657                         seqp = hc->tx_seqh->ccid2s_prev;
658                         break;
659                 }
660         }
661         done = 0;
662         while (1) {
663                 if (seqp->ccid2s_acked) {
664                         done++;
665                         if (done == NUMDUPACK)
666                                 break;
667                 }
668                 if (seqp == hc->tx_seqt)
669                         break;
670                 seqp = seqp->ccid2s_prev;
671         }
672 
673         /* If there are at least 3 acknowledgements, anything unacknowledged
674          * below the last sequence number is considered lost
675          */
676         if (done == NUMDUPACK) {
677                 struct ccid2_seq *last_acked = seqp;
678 
679                 /* check for lost packets */
680                 while (1) {
681                         if (!seqp->ccid2s_acked) {
682                                 ccid2_pr_debug("Packet lost: %llu\n",
683                                                (unsigned long long)seqp->ccid2s_seq);
684                                 /* XXX need to traverse from tail -> head in
685                                  * order to detect multiple congestion events in
686                                  * one ack vector.
687                                  */
688                                 ccid2_congestion_event(sk, seqp);
689                                 hc->tx_pipe--;
690                         }
691                         if (seqp == hc->tx_seqt)
692                                 break;
693                         seqp = seqp->ccid2s_prev;
694                 }
695 
696                 hc->tx_seqt = last_acked;
697         }
698 
699         /* trim acked packets in tail */
700         while (hc->tx_seqt != hc->tx_seqh) {
701                 if (!hc->tx_seqt->ccid2s_acked)
702                         break;
703 
704                 hc->tx_seqt = hc->tx_seqt->ccid2s_next;
705         }
706 
707         /* restart RTO timer if not all outstanding data has been acked */
708         if (hc->tx_pipe == 0)
709                 sk_stop_timer(sk, &hc->tx_rtotimer);
710         else
711                 sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
712 done:
713         /* check if incoming Acks allow pending packets to be sent */
714         if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
715                 dccp_tasklet_schedule(sk);
716         dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
717 }
718 
719 static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
720 {
721         struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
722         struct dccp_sock *dp = dccp_sk(sk);
723         u32 max_ratio;
724 
725         /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
726         hc->tx_ssthresh = ~0U;
727 
728         /* Use larger initial windows (RFC 4341, section 5). */
729         hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
730         hc->tx_expected_wnd = hc->tx_cwnd;
731 
732         /* Make sure that Ack Ratio is enabled and within bounds. */
733         max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
734         if (dp->dccps_l_ack_ratio == 0 || dp->dccps_l_ack_ratio > max_ratio)
735                 dp->dccps_l_ack_ratio = max_ratio;
736 
737         /* XXX init ~ to window size... */
738         if (ccid2_hc_tx_alloc_seq(hc))
739                 return -ENOMEM;
740 
741         hc->tx_rto       = DCCP_TIMEOUT_INIT;
742         hc->tx_rpdupack  = -1;
743         hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_jiffies32;
744         hc->tx_cwnd_used = 0;
745         hc->sk           = sk;
746         timer_setup(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire, 0);
747         INIT_LIST_HEAD(&hc->tx_av_chunks);
748         return 0;
749 }
750 
751 static void ccid2_hc_tx_exit(struct sock *sk)
752 {
753         struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
754         int i;
755 
756         sk_stop_timer(sk, &hc->tx_rtotimer);
757 
758         for (i = 0; i < hc->tx_seqbufc; i++)
759                 kfree(hc->tx_seqbuf[i]);
760         hc->tx_seqbufc = 0;
761         dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
762 }
763 
764 static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
765 {
766         struct ccid2_hc_rx_sock *hc = ccid2_hc_rx_sk(sk);
767 
768         if (!dccp_data_packet(skb))
769                 return;
770 
771         if (++hc->rx_num_data_pkts >= dccp_sk(sk)->dccps_r_ack_ratio) {
772                 dccp_send_ack(sk);
773                 hc->rx_num_data_pkts = 0;
774         }
775 }
776 
777 struct ccid_operations ccid2_ops = {
778         .ccid_id                  = DCCPC_CCID2,
779         .ccid_name                = "TCP-like",
780         .ccid_hc_tx_obj_size      = sizeof(struct ccid2_hc_tx_sock),
781         .ccid_hc_tx_init          = ccid2_hc_tx_init,
782         .ccid_hc_tx_exit          = ccid2_hc_tx_exit,
783         .ccid_hc_tx_send_packet   = ccid2_hc_tx_send_packet,
784         .ccid_hc_tx_packet_sent   = ccid2_hc_tx_packet_sent,
785         .ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
786         .ccid_hc_tx_packet_recv   = ccid2_hc_tx_packet_recv,
787         .ccid_hc_rx_obj_size      = sizeof(struct ccid2_hc_rx_sock),
788         .ccid_hc_rx_packet_recv   = ccid2_hc_rx_packet_recv,
789 };
790 
791 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
792 module_param(ccid2_debug, bool, 0644);
793 MODULE_PARM_DESC(ccid2_debug, "Enable CCID-2 debug messages");
794 #endif
795 

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