ccid2.c 23.1 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784
/*
 *  Copyright (c) 2005, 2006 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 *
 *  Changes to meet Linux coding standards, and DCCP infrastructure fixes.
 *
 *  Copyright (c) 2006 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * This implementation should follow RFC 4341
 */
#include <linux/slab.h>
#include "../feat.h"
#include "ccid2.h"


#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
static bool ccid2_debug;
#define ccid2_pr_debug(format, a...)	DCCP_PR_DEBUG(ccid2_debug, format, ##a)
#else
#define ccid2_pr_debug(format, a...)
#endif

static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hc)
{
	struct ccid2_seq *seqp;
	int i;

	/* check if we have space to preserve the pointer to the buffer */
	if (hc->tx_seqbufc >= (sizeof(hc->tx_seqbuf) /
			       sizeof(struct ccid2_seq *)))
		return -ENOMEM;

	/* allocate buffer and initialize linked list */
	seqp = kmalloc(CCID2_SEQBUF_LEN * sizeof(struct ccid2_seq), gfp_any());
	if (seqp == NULL)
		return -ENOMEM;

	for (i = 0; i < (CCID2_SEQBUF_LEN - 1); i++) {
		seqp[i].ccid2s_next = &seqp[i + 1];
		seqp[i + 1].ccid2s_prev = &seqp[i];
	}
	seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = seqp;
	seqp->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];

	/* This is the first allocation.  Initiate the head and tail.  */
	if (hc->tx_seqbufc == 0)
		hc->tx_seqh = hc->tx_seqt = seqp;
	else {
		/* link the existing list with the one we just created */
		hc->tx_seqh->ccid2s_next = seqp;
		seqp->ccid2s_prev = hc->tx_seqh;

		hc->tx_seqt->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
		seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = hc->tx_seqt;
	}

	/* store the original pointer to the buffer so we can free it */
	hc->tx_seqbuf[hc->tx_seqbufc] = seqp;
	hc->tx_seqbufc++;

	return 0;
}

static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
{
	if (ccid2_cwnd_network_limited(ccid2_hc_tx_sk(sk)))
		return CCID_PACKET_WILL_DEQUEUE_LATER;
	return CCID_PACKET_SEND_AT_ONCE;
}

static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
{
	u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);

	/*
	 * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
	 * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
	 * acceptable since this causes starvation/deadlock whenever cwnd < 2.
	 * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
	 */
	if (val == 0 || val > max_ratio) {
		DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
		val = max_ratio;
	}
	dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
				   min_t(u32, val, DCCPF_ACK_RATIO_MAX));
}

static void ccid2_check_l_ack_ratio(struct sock *sk)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);

	/*
	 * After a loss, idle period, application limited period, or RTO we
	 * need to check that the ack ratio is still less than the congestion
	 * window. Otherwise, we will send an entire congestion window of
	 * packets and got no response because we haven't sent ack ratio
	 * packets yet.
	 * If the ack ratio does need to be reduced, we reduce it to half of
	 * the congestion window (or 1 if that's zero) instead of to the
	 * congestion window. This prevents problems if one ack is lost.
	 */
	if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
		ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
}

static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
{
	dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
				   clamp_val(val, DCCPF_SEQ_WMIN,
						  DCCPF_SEQ_WMAX));
}

static void ccid2_hc_tx_rto_expire(unsigned long data)
{
	struct sock *sk = (struct sock *)data;
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);

	bh_lock_sock(sk);
	if (sock_owned_by_user(sk)) {
		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
		goto out;
	}

	ccid2_pr_debug("RTO_EXPIRE\n");

	/* back-off timer */
	hc->tx_rto <<= 1;
	if (hc->tx_rto > DCCP_RTO_MAX)
		hc->tx_rto = DCCP_RTO_MAX;

	/* adjust pipe, cwnd etc */
	hc->tx_ssthresh = hc->tx_cwnd / 2;
	if (hc->tx_ssthresh < 2)
		hc->tx_ssthresh = 2;
	hc->tx_cwnd	= 1;
	hc->tx_pipe	= 0;

	/* clear state about stuff we sent */
	hc->tx_seqt = hc->tx_seqh;
	hc->tx_packets_acked = 0;

	/* clear ack ratio state. */
	hc->tx_rpseq    = 0;
	hc->tx_rpdupack = -1;
	ccid2_change_l_ack_ratio(sk, 1);

	/* if we were blocked before, we may now send cwnd=1 packet */
	if (sender_was_blocked)
		tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
	/* restart backed-off timer */
	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
out:
	bh_unlock_sock(sk);
	sock_put(sk);
}

/*
 *	Congestion window validation (RFC 2861).
 */
static bool ccid2_do_cwv = true;
module_param(ccid2_do_cwv, bool, 0644);
MODULE_PARM_DESC(ccid2_do_cwv, "Perform RFC2861 Congestion Window Validation");

/**
 * ccid2_update_used_window  -  Track how much of cwnd is actually used
 * This is done in addition to CWV. The sender needs to have an idea of how many
 * packets may be in flight, to set the local Sequence Window value accordingly
 * (RFC 4340, 7.5.2). The CWV mechanism is exploited to keep track of the
 * maximum-used window. We use an EWMA low-pass filter to filter out noise.
 */
static void ccid2_update_used_window(struct ccid2_hc_tx_sock *hc, u32 new_wnd)
{
	hc->tx_expected_wnd = (3 * hc->tx_expected_wnd + new_wnd) / 4;
}

/* This borrows the code of tcp_cwnd_application_limited() */
static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	/* don't reduce cwnd below the initial window (IW) */
	u32 init_win = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache),
	    win_used = max(hc->tx_cwnd_used, init_win);

	if (win_used < hc->tx_cwnd) {
		hc->tx_ssthresh = max(hc->tx_ssthresh,
				     (hc->tx_cwnd >> 1) + (hc->tx_cwnd >> 2));
		hc->tx_cwnd = (hc->tx_cwnd + win_used) >> 1;
	}
	hc->tx_cwnd_used  = 0;
	hc->tx_cwnd_stamp = now;

	ccid2_check_l_ack_ratio(sk);
}

/* This borrows the code of tcp_cwnd_restart() */
static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	u32 cwnd = hc->tx_cwnd, restart_cwnd,
	    iwnd = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache);

	hc->tx_ssthresh = max(hc->tx_ssthresh, (cwnd >> 1) + (cwnd >> 2));

	/* don't reduce cwnd below the initial window (IW) */
	restart_cwnd = min(cwnd, iwnd);
	cwnd >>= (now - hc->tx_lsndtime) / hc->tx_rto;
	hc->tx_cwnd = max(cwnd, restart_cwnd);

	hc->tx_cwnd_stamp = now;
	hc->tx_cwnd_used  = 0;

	ccid2_check_l_ack_ratio(sk);
}

static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	const u32 now = ccid2_time_stamp;
	struct ccid2_seq *next;

	/* slow-start after idle periods (RFC 2581, RFC 2861) */
	if (ccid2_do_cwv && !hc->tx_pipe &&
	    (s32)(now - hc->tx_lsndtime) >= hc->tx_rto)
		ccid2_cwnd_restart(sk, now);

	hc->tx_lsndtime = now;
	hc->tx_pipe    += 1;

	/* see whether cwnd was fully used (RFC 2861), update expected window */
	if (ccid2_cwnd_network_limited(hc)) {
		ccid2_update_used_window(hc, hc->tx_cwnd);
		hc->tx_cwnd_used  = 0;
		hc->tx_cwnd_stamp = now;
	} else {
		if (hc->tx_pipe > hc->tx_cwnd_used)
			hc->tx_cwnd_used = hc->tx_pipe;

		ccid2_update_used_window(hc, hc->tx_cwnd_used);

		if (ccid2_do_cwv && (s32)(now - hc->tx_cwnd_stamp) >= hc->tx_rto)
			ccid2_cwnd_application_limited(sk, now);
	}

	hc->tx_seqh->ccid2s_seq   = dp->dccps_gss;
	hc->tx_seqh->ccid2s_acked = 0;
	hc->tx_seqh->ccid2s_sent  = now;

	next = hc->tx_seqh->ccid2s_next;
	/* check if we need to alloc more space */
	if (next == hc->tx_seqt) {
		if (ccid2_hc_tx_alloc_seq(hc)) {
			DCCP_CRIT("packet history - out of memory!");
			/* FIXME: find a more graceful way to bail out */
			return;
		}
		next = hc->tx_seqh->ccid2s_next;
		BUG_ON(next == hc->tx_seqt);
	}
	hc->tx_seqh = next;

	ccid2_pr_debug("cwnd=%d pipe=%d\n", hc->tx_cwnd, hc->tx_pipe);

	/*
	 * FIXME: The code below is broken and the variables have been removed
	 * from the socket struct. The `ackloss' variable was always set to 0,
	 * and with arsent there are several problems:
	 *  (i) it doesn't just count the number of Acks, but all sent packets;
	 *  (ii) it is expressed in # of packets, not # of windows, so the
	 *  comparison below uses the wrong formula: Appendix A of RFC 4341
	 *  comes up with the number K = cwnd / (R^2 - R) of consecutive windows
	 *  of data with no lost or marked Ack packets. If arsent were the # of
	 *  consecutive Acks received without loss, then Ack Ratio needs to be
	 *  decreased by 1 when
	 *	      arsent >=  K * cwnd / R  =  cwnd^2 / (R^3 - R^2)
	 *  where cwnd / R is the number of Acks received per window of data
	 *  (cf. RFC 4341, App. A). The problems are that
	 *  - arsent counts other packets as well;
	 *  - the comparison uses a formula different from RFC 4341;
	 *  - computing a cubic/quadratic equation each time is too complicated.
	 *  Hence a different algorithm is needed.
	 */
#if 0
	/* Ack Ratio.  Need to maintain a concept of how many windows we sent */
	hc->tx_arsent++;
	/* We had an ack loss in this window... */
	if (hc->tx_ackloss) {
		if (hc->tx_arsent >= hc->tx_cwnd) {
			hc->tx_arsent  = 0;
			hc->tx_ackloss = 0;
		}
	} else {
		/* No acks lost up to now... */
		/* decrease ack ratio if enough packets were sent */
		if (dp->dccps_l_ack_ratio > 1) {
			/* XXX don't calculate denominator each time */
			int denom = dp->dccps_l_ack_ratio * dp->dccps_l_ack_ratio -
				    dp->dccps_l_ack_ratio;

			denom = hc->tx_cwnd * hc->tx_cwnd / denom;

			if (hc->tx_arsent >= denom) {
				ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
				hc->tx_arsent = 0;
			}
		} else {
			/* we can't increase ack ratio further [1] */
			hc->tx_arsent = 0; /* or maybe set it to cwnd*/
		}
	}
#endif

	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
	do {
		struct ccid2_seq *seqp = hc->tx_seqt;

		while (seqp != hc->tx_seqh) {
			ccid2_pr_debug("out seq=%llu acked=%d time=%u\n",
				       (unsigned long long)seqp->ccid2s_seq,
				       seqp->ccid2s_acked, seqp->ccid2s_sent);
			seqp = seqp->ccid2s_next;
		}
	} while (0);
	ccid2_pr_debug("=========\n");
#endif
}

/**
 * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
 * This code is almost identical with TCP's tcp_rtt_estimator(), since
 * - it has a higher sampling frequency (recommended by RFC 1323),
 * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
 * - it is simple (cf. more complex proposals such as Eifel timer or research
 *   which suggests that the gain should be set according to window size),
 * - in tests it was found to work well with CCID2 [gerrit].
 */
static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	long m = mrtt ? : 1;

	if (hc->tx_srtt == 0) {
		/* First measurement m */
		hc->tx_srtt = m << 3;
		hc->tx_mdev = m << 1;

		hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
		hc->tx_rttvar   = hc->tx_mdev_max;

		hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
	} else {
		/* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
		m -= (hc->tx_srtt >> 3);
		hc->tx_srtt += m;

		/* Similarly, update scaled mdev with regard to |m| */
		if (m < 0) {
			m = -m;
			m -= (hc->tx_mdev >> 2);
			/*
			 * This neutralises RTO increase when RTT < SRTT - mdev
			 * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
			 * in Linux TCP", USENIX 2002, pp. 49-62).
			 */
			if (m > 0)
				m >>= 3;
		} else {
			m -= (hc->tx_mdev >> 2);
		}
		hc->tx_mdev += m;

		if (hc->tx_mdev > hc->tx_mdev_max) {
			hc->tx_mdev_max = hc->tx_mdev;
			if (hc->tx_mdev_max > hc->tx_rttvar)
				hc->tx_rttvar = hc->tx_mdev_max;
		}

		/*
		 * Decay RTTVAR at most once per flight, exploiting that
		 *  1) pipe <= cwnd <= Sequence_Window = W  (RFC 4340, 7.5.2)
		 *  2) AWL = GSS-W+1 <= GAR <= GSS          (RFC 4340, 7.5.1)
		 * GAR is a useful bound for FlightSize = pipe.
		 * AWL is probably too low here, as it over-estimates pipe.
		 */
		if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
			if (hc->tx_mdev_max < hc->tx_rttvar)
				hc->tx_rttvar -= (hc->tx_rttvar -
						  hc->tx_mdev_max) >> 2;
			hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
			hc->tx_mdev_max = tcp_rto_min(sk);
		}
	}

	/*
	 * Set RTO from SRTT and RTTVAR
	 * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
	 * This agrees with RFC 4341, 5:
	 *	"Because DCCP does not retransmit data, DCCP does not require
	 *	 TCP's recommended minimum timeout of one second".
	 */
	hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;

	if (hc->tx_rto > DCCP_RTO_MAX)
		hc->tx_rto = DCCP_RTO_MAX;
}

static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
			  unsigned int *maxincr)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	struct dccp_sock *dp = dccp_sk(sk);
	int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;

	if (hc->tx_cwnd < dp->dccps_l_seq_win &&
	    r_seq_used < dp->dccps_r_seq_win) {
		if (hc->tx_cwnd < hc->tx_ssthresh) {
			if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) {
				hc->tx_cwnd += 1;
				*maxincr    -= 1;
				hc->tx_packets_acked = 0;
			}
		} else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
			hc->tx_cwnd += 1;
			hc->tx_packets_acked = 0;
		}
	}

	/*
	 * Adjust the local sequence window and the ack ratio to allow about
	 * 5 times the number of packets in the network (RFC 4340 7.5.2)
	 */
	if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2);
	else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2)
		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U);

	if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2);
	else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2)
		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2);

	/*
	 * FIXME: RTT is sampled several times per acknowledgment (for each
	 * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
	 * This causes the RTT to be over-estimated, since the older entries
	 * in the Ack Vector have earlier sending times.
	 * The cleanest solution is to not use the ccid2s_sent field at all
	 * and instead use DCCP timestamps: requires changes in other places.
	 */
	ccid2_rtt_estimator(sk, ccid2_time_stamp - seqp->ccid2s_sent);
}

static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);

	if ((s32)(seqp->ccid2s_sent - hc->tx_last_cong) < 0) {
		ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
		return;
	}

	hc->tx_last_cong = ccid2_time_stamp;

	hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
	hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);

	ccid2_check_l_ack_ratio(sk);
}

static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
				     u8 option, u8 *optval, u8 optlen)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);

	switch (option) {
	case DCCPO_ACK_VECTOR_0:
	case DCCPO_ACK_VECTOR_1:
		return dccp_ackvec_parsed_add(&hc->tx_av_chunks, optval, optlen,
					      option - DCCPO_ACK_VECTOR_0);
	}
	return 0;
}

static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
	struct dccp_ackvec_parsed *avp;
	u64 ackno, seqno;
	struct ccid2_seq *seqp;
	int done = 0;
	unsigned int maxincr = 0;

	/* check reverse path congestion */
	seqno = DCCP_SKB_CB(skb)->dccpd_seq;

	/* XXX this whole "algorithm" is broken.  Need to fix it to keep track
	 * of the seqnos of the dupacks so that rpseq and rpdupack are correct
	 * -sorbo.
	 */
	/* need to bootstrap */
	if (hc->tx_rpdupack == -1) {
		hc->tx_rpdupack = 0;
		hc->tx_rpseq    = seqno;
	} else {
		/* check if packet is consecutive */
		if (dccp_delta_seqno(hc->tx_rpseq, seqno) == 1)
			hc->tx_rpseq = seqno;
		/* it's a later packet */
		else if (after48(seqno, hc->tx_rpseq)) {
			hc->tx_rpdupack++;

			/* check if we got enough dupacks */
			if (hc->tx_rpdupack >= NUMDUPACK) {
				hc->tx_rpdupack = -1; /* XXX lame */
				hc->tx_rpseq    = 0;
#ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
				/*
				 * FIXME: Ack Congestion Control is broken; in
				 * the current state instabilities occurred with
				 * Ack Ratios greater than 1; causing hang-ups
				 * and long RTO timeouts. This needs to be fixed
				 * before opening up dynamic changes. -- gerrit
				 */
				ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
#endif
			}
		}
	}

	/* check forward path congestion */
	if (dccp_packet_without_ack(skb))
		return;

	/* still didn't send out new data packets */
	if (hc->tx_seqh == hc->tx_seqt)
		goto done;

	ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
	if (after48(ackno, hc->tx_high_ack))
		hc->tx_high_ack = ackno;

	seqp = hc->tx_seqt;
	while (before48(seqp->ccid2s_seq, ackno)) {
		seqp = seqp->ccid2s_next;
		if (seqp == hc->tx_seqh) {
			seqp = hc->tx_seqh->ccid2s_prev;
			break;
		}
	}

	/*
	 * In slow-start, cwnd can increase up to a maximum of Ack Ratio/2
	 * packets per acknowledgement. Rounding up avoids that cwnd is not
	 * advanced when Ack Ratio is 1 and gives a slight edge otherwise.
	 */
	if (hc->tx_cwnd < hc->tx_ssthresh)
		maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);

	/* go through all ack vectors */
	list_for_each_entry(avp, &hc->tx_av_chunks, node) {
		/* go through this ack vector */
		for (; avp->len--; avp->vec++) {
			u64 ackno_end_rl = SUB48(ackno,
						 dccp_ackvec_runlen(avp->vec));

			ccid2_pr_debug("ackvec %llu |%u,%u|\n",
				       (unsigned long long)ackno,
				       dccp_ackvec_state(avp->vec) >> 6,
				       dccp_ackvec_runlen(avp->vec));
			/* if the seqno we are analyzing is larger than the
			 * current ackno, then move towards the tail of our
			 * seqnos.
			 */
			while (after48(seqp->ccid2s_seq, ackno)) {
				if (seqp == hc->tx_seqt) {
					done = 1;
					break;
				}
				seqp = seqp->ccid2s_prev;
			}
			if (done)
				break;

			/* check all seqnos in the range of the vector
			 * run length
			 */
			while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
				const u8 state = dccp_ackvec_state(avp->vec);

				/* new packet received or marked */
				if (state != DCCPAV_NOT_RECEIVED &&
				    !seqp->ccid2s_acked) {
					if (state == DCCPAV_ECN_MARKED)
						ccid2_congestion_event(sk,
								       seqp);
					else
						ccid2_new_ack(sk, seqp,
							      &maxincr);

					seqp->ccid2s_acked = 1;
					ccid2_pr_debug("Got ack for %llu\n",
						       (unsigned long long)seqp->ccid2s_seq);
					hc->tx_pipe--;
				}
				if (seqp == hc->tx_seqt) {
					done = 1;
					break;
				}
				seqp = seqp->ccid2s_prev;
			}
			if (done)
				break;

			ackno = SUB48(ackno_end_rl, 1);
		}
		if (done)
			break;
	}

	/* The state about what is acked should be correct now
	 * Check for NUMDUPACK
	 */
	seqp = hc->tx_seqt;
	while (before48(seqp->ccid2s_seq, hc->tx_high_ack)) {
		seqp = seqp->ccid2s_next;
		if (seqp == hc->tx_seqh) {
			seqp = hc->tx_seqh->ccid2s_prev;
			break;
		}
	}
	done = 0;
	while (1) {
		if (seqp->ccid2s_acked) {
			done++;
			if (done == NUMDUPACK)
				break;
		}
		if (seqp == hc->tx_seqt)
			break;
		seqp = seqp->ccid2s_prev;
	}

	/* If there are at least 3 acknowledgements, anything unacknowledged
	 * below the last sequence number is considered lost
	 */
	if (done == NUMDUPACK) {
		struct ccid2_seq *last_acked = seqp;

		/* check for lost packets */
		while (1) {
			if (!seqp->ccid2s_acked) {
				ccid2_pr_debug("Packet lost: %llu\n",
					       (unsigned long long)seqp->ccid2s_seq);
				/* XXX need to traverse from tail -> head in
				 * order to detect multiple congestion events in
				 * one ack vector.
				 */
				ccid2_congestion_event(sk, seqp);
				hc->tx_pipe--;
			}
			if (seqp == hc->tx_seqt)
				break;
			seqp = seqp->ccid2s_prev;
		}

		hc->tx_seqt = last_acked;
	}

	/* trim acked packets in tail */
	while (hc->tx_seqt != hc->tx_seqh) {
		if (!hc->tx_seqt->ccid2s_acked)
			break;

		hc->tx_seqt = hc->tx_seqt->ccid2s_next;
	}

	/* restart RTO timer if not all outstanding data has been acked */
	if (hc->tx_pipe == 0)
		sk_stop_timer(sk, &hc->tx_rtotimer);
	else
		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
done:
	/* check if incoming Acks allow pending packets to be sent */
	if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
		tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
	dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
}

static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
{
	struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
	struct dccp_sock *dp = dccp_sk(sk);
	u32 max_ratio;

	/* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
	hc->tx_ssthresh = ~0U;

	/* Use larger initial windows (RFC 4341, section 5). */
	hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
	hc->tx_expected_wnd = hc->tx_cwnd;

	/* Make sure that Ack Ratio is enabled and within bounds. */
	max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
	if (dp->dccps_l_ack_ratio == 0 || dp->dccps_l_ack_ratio > max_ratio)
		dp->dccps_l_ack_ratio = max_ratio;

	/* XXX init ~ to window size... */
	if (ccid2_hc_tx_alloc_seq(hc))
		return -ENOMEM;

	hc->tx_rto	 = DCCP_TIMEOUT_INIT;
	hc->tx_rpdupack  = -1;
	hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_time_stamp;
	hc->tx_cwnd_used = 0;
	setup_timer(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire,
			(unsigned long)sk);
	INIT_LIST_HEAD(&hc->tx_av_chunks);
	return 0;
}

static void ccid2_hc_tx_exit(struct sock *sk)
{
	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
	int i;

	sk_stop_timer(sk, &hc->tx_rtotimer);

	for (i = 0; i < hc->tx_seqbufc; i++)
		kfree(hc->tx_seqbuf[i]);
	hc->tx_seqbufc = 0;
}

static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
	struct ccid2_hc_rx_sock *hc = ccid2_hc_rx_sk(sk);

	if (!dccp_data_packet(skb))
		return;

	if (++hc->rx_num_data_pkts >= dccp_sk(sk)->dccps_r_ack_ratio) {
		dccp_send_ack(sk);
		hc->rx_num_data_pkts = 0;
	}
}

struct ccid_operations ccid2_ops = {
	.ccid_id		  = DCCPC_CCID2,
	.ccid_name		  = "TCP-like",
	.ccid_hc_tx_obj_size	  = sizeof(struct ccid2_hc_tx_sock),
	.ccid_hc_tx_init	  = ccid2_hc_tx_init,
	.ccid_hc_tx_exit	  = ccid2_hc_tx_exit,
	.ccid_hc_tx_send_packet	  = ccid2_hc_tx_send_packet,
	.ccid_hc_tx_packet_sent	  = ccid2_hc_tx_packet_sent,
	.ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
	.ccid_hc_tx_packet_recv	  = ccid2_hc_tx_packet_recv,
	.ccid_hc_rx_obj_size	  = sizeof(struct ccid2_hc_rx_sock),
	.ccid_hc_rx_packet_recv	  = ccid2_hc_rx_packet_recv,
};

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
module_param(ccid2_debug, bool, 0644);
MODULE_PARM_DESC(ccid2_debug, "Enable CCID-2 debug messages");
#endif