aboutsummaryrefslogtreecommitdiffstats
path: root/net/dccp/output.c
blob: fea30cdc0bee00af3096859e3c07cb1355c3745e (plain) (blame)
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
/*
 *  net/dccp/output.c
 *
 *  An implementation of the DCCP protocol
 *  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.
 */

#include <linux/dccp.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>

#include <net/inet_sock.h>
#include <net/sock.h>

#include "ackvec.h"
#include "ccid.h"
#include "dccp.h"

static inline void dccp_event_ack_sent(struct sock *sk)
{
	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
}

static void dccp_skb_entail(struct sock *sk, struct sk_buff *skb)
{
	skb_set_owner_w(skb, sk);
	WARN_ON(sk->sk_send_head);
	sk->sk_send_head = skb;
}

/*
 * All SKB's seen here are completely headerless. It is our
 * job to build the DCCP header, and pass the packet down to
 * IP so it can do the same plus pass the packet off to the
 * device.
 */
static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
{
	if (likely(skb != NULL)) {
		const struct inet_sock *inet = inet_sk(sk);
		const struct inet_connection_sock *icsk = inet_csk(sk);
		struct dccp_sock *dp = dccp_sk(sk);
		struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
		struct dccp_hdr *dh;
		/* XXX For now we're using only 48 bits sequence numbers */
		const u32 dccp_header_size = sizeof(*dh) +
					     sizeof(struct dccp_hdr_ext) +
					  dccp_packet_hdr_len(dcb->dccpd_type);
		int err, set_ack = 1;
		u64 ackno = dp->dccps_gsr;
		/*
		 * Increment GSS here already in case the option code needs it.
		 * Update GSS for real only if option processing below succeeds.
		 */
		dcb->dccpd_seq = ADD48(dp->dccps_gss, 1);

		switch (dcb->dccpd_type) {
		case DCCP_PKT_DATA:
			set_ack = 0;
			/* fall through */
		case DCCP_PKT_DATAACK:
		case DCCP_PKT_RESET:
			break;

		case DCCP_PKT_REQUEST:
			set_ack = 0;
			/* Use ISS on the first (non-retransmitted) Request. */
			if (icsk->icsk_retransmits == 0)
				dcb->dccpd_seq = dp->dccps_iss;
			/* fall through */

		case DCCP_PKT_SYNC:
		case DCCP_PKT_SYNCACK:
			ackno = dcb->dccpd_ack_seq;
			/* fall through */
		default:
			/*
			 * Set owner/destructor: some skbs are allocated via
			 * alloc_skb (e.g. when retransmission may happen).
			 * Only Data, DataAck, and Reset packets should come
			 * through here with skb->sk set.
			 */
			WARN_ON(skb->sk);
			skb_set_owner_w(skb, sk);
			break;
		}

		if (dccp_insert_options(sk, skb)) {
			kfree_skb(skb);
			return -EPROTO;
		}


		/* Build DCCP header and checksum it. */
		dh = dccp_zeroed_hdr(skb, dccp_header_size);
		dh->dccph_type	= dcb->dccpd_type;
		dh->dccph_sport	= inet->sport;
		dh->dccph_dport	= inet->dport;
		dh->dccph_doff	= (dccp_header_size + dcb->dccpd_opt_len) / 4;
		dh->dccph_ccval	= dcb->dccpd_ccval;
		dh->dccph_cscov = dp->dccps_pcslen;
		/* XXX For now we're using only 48 bits sequence numbers */
		dh->dccph_x	= 1;

		dccp_update_gss(sk, dcb->dccpd_seq);
		dccp_hdr_set_seq(dh, dp->dccps_gss);
		if (set_ack)
			dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), ackno);

		switch (dcb->dccpd_type) {
		case DCCP_PKT_REQUEST:
			dccp_hdr_request(skb)->dccph_req_service =
							dp->dccps_service;
			/*
			 * Limit Ack window to ISS <= P.ackno <= GSS, so that
			 * only Responses to Requests we sent are considered.
			 */
			dp->dccps_awl = dp->dccps_iss;
			break;
		case DCCP_PKT_RESET:
			dccp_hdr_reset(skb)->dccph_reset_code =
							dcb->dccpd_reset_code;
			break;
		}

		icsk->icsk_af_ops->send_check(sk, 0, skb);

		if (set_ack)
			dccp_event_ack_sent(sk);

		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);

		err = icsk->icsk_af_ops->queue_xmit(skb, 0);
		return net_xmit_eval(err);
	}
	return -ENOBUFS;
}

/**
 * dccp_determine_ccmps  -  Find out about CCID-specfic packet-size limits
 * We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
 * since the RX CCID is restricted to feedback packets (Acks), which are small
 * in comparison with the data traffic. A value of 0 means "no current CCMPS".
 */
static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
{
	const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;

	if (tx_ccid == NULL || tx_ccid->ccid_ops == NULL)
		return 0;
	return tx_ccid->ccid_ops->ccid_ccmps;
}

unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct dccp_sock *dp = dccp_sk(sk);
	u32 ccmps = dccp_determine_ccmps(dp);
	int cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;

	/* Account for header lengths and IPv4/v6 option overhead */
	cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
		    sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));

	/*
	 * FIXME: this should come from the CCID infrastructure, where, say,
	 * TFRC will say it wants TIMESTAMPS, ELAPSED time, etc, for now lets
	 * put a rough estimate for NDP + TIMESTAMP + TIMESTAMP_ECHO + ELAPSED
	 * TIME + TFRC_OPT_LOSS_EVENT_RATE + TFRC_OPT_RECEIVE_RATE + padding to
	 * make it a multiple of 4
	 */

	cur_mps -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;

	/* And store cached results */
	icsk->icsk_pmtu_cookie = pmtu;
	dp->dccps_mss_cache = cur_mps;

	return cur_mps;
}

EXPORT_SYMBOL_GPL(dccp_sync_mss);

void dccp_write_space(struct sock *sk)
{
	read_lock(&sk->sk_callback_lock);

	if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
		wake_up_interruptible(sk->sk_sleep);
	/* Should agree with poll, otherwise some programs break */
	if (sock_writeable(sk))
		sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);

	read_unlock(&sk->sk_callback_lock);
}

/**
 * dccp_wait_for_ccid - Wait for ccid to tell us we can send a packet
 * @sk:    socket to wait for
 * @skb:   current skb to pass on for waiting
 * @delay: sleep timeout in milliseconds (> 0)
 * This function is called by default when the socket is closed, and
 * when a non-zero linger time is set on the socket. For consistency
 */
static int dccp_wait_for_ccid(struct sock *sk, struct sk_buff *skb, int delay)
{
	struct dccp_sock *dp = dccp_sk(sk);
	DEFINE_WAIT(wait);
	unsigned long jiffdelay;
	int rc;

	do {
		dccp_pr_debug("delayed send by %d msec\n", delay);
		jiffdelay = msecs_to_jiffies(delay);

		prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);

		sk->sk_write_pending++;
		release_sock(sk);
		schedule_timeout(jiffdelay);
		lock_sock(sk);
		sk->sk_write_pending--;

		if (sk->sk_err)
			goto do_error;
		if (signal_pending(current))
			goto do_interrupted;

		rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
	} while ((delay = rc) > 0);
out:
	finish_wait(sk->sk_sleep, &wait);
	return rc;

do_error:
	rc = -EPIPE;
	goto out;
do_interrupted:
	rc = -EINTR;
	goto out;
}

void dccp_write_xmit(struct sock *sk, int block)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;

	while ((skb = skb_peek(&sk->sk_write_queue))) {
		int err = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

		if (err > 0) {
			if (!block) {
				sk_reset_timer(sk, &dp->dccps_xmit_timer,
						msecs_to_jiffies(err)+jiffies);
				break;
			} else
				err = dccp_wait_for_ccid(sk, skb, err);
			if (err && err != -EINTR)
				DCCP_BUG("err=%d after dccp_wait_for_ccid", err);
		}

		skb_dequeue(&sk->sk_write_queue);
		if (err == 0) {
			struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
			const int len = skb->len;

			if (sk->sk_state == DCCP_PARTOPEN) {
				/* See 8.1.5.  Handshake Completion */
				inet_csk_schedule_ack(sk);
				inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
						  inet_csk(sk)->icsk_rto,
						  DCCP_RTO_MAX);
				dcb->dccpd_type = DCCP_PKT_DATAACK;
			} else if (dccp_ack_pending(sk))
				dcb->dccpd_type = DCCP_PKT_DATAACK;
			else
				dcb->dccpd_type = DCCP_PKT_DATA;

			err = dccp_transmit_skb(sk, skb);
			ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
			if (err)
				DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
					 err);
		} else {
			dccp_pr_debug("packet discarded due to err=%d\n", err);
			kfree_skb(skb);
		}
	}
}

/**
 * dccp_retransmit_skb  -  Retransmit Request, Close, or CloseReq packets
 * There are only four retransmittable packet types in DCCP:
 * - Request  in client-REQUEST  state (sec. 8.1.1),
 * - CloseReq in server-CLOSEREQ state (sec. 8.3),
 * - Close    in   node-CLOSING  state (sec. 8.3),
 * - Acks in client-PARTOPEN state (sec. 8.1.5, handled by dccp_delack_timer()).
 * This function expects sk->sk_send_head to contain the original skb.
 */
int dccp_retransmit_skb(struct sock *sk)
{
	WARN_ON(sk->sk_send_head == NULL);

	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
		return -EHOSTUNREACH; /* Routing failure or similar. */

	/* this count is used to distinguish original and retransmitted skb */
	inet_csk(sk)->icsk_retransmits++;

	return dccp_transmit_skb(sk, skb_clone(sk->sk_send_head, GFP_ATOMIC));
}

struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
				   struct request_sock *req)
{
	struct dccp_hdr *dh;
	struct dccp_request_sock *dreq;
	const u32 dccp_header_size = sizeof(struct dccp_hdr) +
				     sizeof(struct dccp_hdr_ext) +
				     sizeof(struct dccp_hdr_response);
	struct sk_buff *skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1,
					   GFP_ATOMIC);
	if (skb == NULL)
		return NULL;

	/* Reserve space for headers. */
	skb_reserve(skb, sk->sk_prot->max_header);

	skb->dst = dst_clone(dst);

	dreq = dccp_rsk(req);
	if (inet_rsk(req)->acked)	/* increase ISS upon retransmission */
		dccp_inc_seqno(&dreq->dreq_iss);
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
	DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;

	/* Resolve feature dependencies resulting from choice of CCID */
	if (dccp_feat_server_ccid_dependencies(dreq))
		goto response_failed;

	if (dccp_insert_options_rsk(dreq, skb))
		goto response_failed;

	/* Build and checksum header */
	dh = dccp_zeroed_hdr(skb, dccp_header_size);

	dh->dccph_sport	= inet_rsk(req)->loc_port;
	dh->dccph_dport	= inet_rsk(req)->rmt_port;
	dh->dccph_doff	= (dccp_header_size +
			   DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
	dh->dccph_type	= DCCP_PKT_RESPONSE;
	dh->dccph_x	= 1;
	dccp_hdr_set_seq(dh, dreq->dreq_iss);
	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
	dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;

	dccp_csum_outgoing(skb);

	/* We use `acked' to remember that a Response was already sent. */
	inet_rsk(req)->acked = 1;
	DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
	return skb;
response_failed:
	kfree_skb(skb);
	return NULL;
}

EXPORT_SYMBOL_GPL(dccp_make_response);

/* answer offending packet in @rcv_skb with Reset from control socket @ctl */
struct sk_buff *dccp_ctl_make_reset(struct sock *sk, struct sk_buff *rcv_skb)
{
	struct dccp_hdr *rxdh = dccp_hdr(rcv_skb), *dh;
	struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
	const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
				       sizeof(struct dccp_hdr_ext) +
				       sizeof(struct dccp_hdr_reset);
	struct dccp_hdr_reset *dhr;
	struct sk_buff *skb;

	skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);
	if (skb == NULL)
		return NULL;

	skb_reserve(skb, sk->sk_prot->max_header);

	/* Swap the send and the receive. */
	dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
	dh->dccph_type	= DCCP_PKT_RESET;
	dh->dccph_sport	= rxdh->dccph_dport;
	dh->dccph_dport	= rxdh->dccph_sport;
	dh->dccph_doff	= dccp_hdr_reset_len / 4;
	dh->dccph_x	= 1;

	dhr = dccp_hdr_reset(skb);
	dhr->dccph_reset_code = dcb->dccpd_reset_code;

	switch (dcb->dccpd_reset_code) {
	case DCCP_RESET_CODE_PACKET_ERROR:
		dhr->dccph_reset_data[0] = rxdh->dccph_type;
		break;
	case DCCP_RESET_CODE_OPTION_ERROR:	/* fall through */
	case DCCP_RESET_CODE_MANDATORY_ERROR:
		memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
		break;
	}
	/*
	 * From RFC 4340, 8.3.1:
	 *   If P.ackno exists, set R.seqno := P.ackno + 1.
	 *   Else set R.seqno := 0.
	 */
	if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
		dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);

	dccp_csum_outgoing(skb);
	return skb;
}

EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);

/* send Reset on established socket, to close or abort the connection */
int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
{
	struct sk_buff *skb;
	/*
	 * FIXME: what if rebuild_header fails?
	 * Should we be doing a rebuild_header here?
	 */
	int err = inet_csk(sk)->icsk_af_ops->rebuild_header(sk);

	if (err != 0)
		return err;

	skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1, GFP_ATOMIC);
	if (skb == NULL)
		return -ENOBUFS;

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	DCCP_SKB_CB(skb)->dccpd_type	   = DCCP_PKT_RESET;
	DCCP_SKB_CB(skb)->dccpd_reset_code = code;

	return dccp_transmit_skb(sk, skb);
}

/*
 * Do all connect socket setups that can be done AF independent.
 */
static inline void dccp_connect_init(struct sock *sk)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);

	dccp_sync_mss(sk, dst_mtu(dst));

	/* Initialise GAR as per 8.5; AWL/AWH are set in dccp_transmit_skb() */
	dp->dccps_gar = dp->dccps_iss;

	icsk->icsk_retransmits = 0;
}

int dccp_connect(struct sock *sk)
{
	struct sk_buff *skb;
	struct inet_connection_sock *icsk = inet_csk(sk);

	/* do not connect if feature negotiation setup fails */
	if (dccp_feat_finalise_settings(dccp_sk(sk)))
		return -EPROTO;

	dccp_connect_init(sk);

	skb = alloc_skb(sk->sk_prot->max_header, sk->sk_allocation);
	if (unlikely(skb == NULL))
		return -ENOBUFS;

	/* Reserve space for headers. */
	skb_reserve(skb, sk->sk_prot->max_header);

	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;

	dccp_skb_entail(sk, skb);
	dccp_transmit_skb(sk, skb_clone(skb, GFP_KERNEL));
	DCCP_INC_STATS(DCCP_MIB_ACTIVEOPENS);

	/* Timer for repeating the REQUEST until an answer. */
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  icsk->icsk_rto, DCCP_RTO_MAX);
	return 0;
}

EXPORT_SYMBOL_GPL(dccp_connect);

void dccp_send_ack(struct sock *sk)
{
	/* If we have been reset, we may not send again. */
	if (sk->sk_state != DCCP_CLOSED) {
		struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header,
						GFP_ATOMIC);

		if (skb == NULL) {
			inet_csk_schedule_ack(sk);
			inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
						  TCP_DELACK_MAX,
						  DCCP_RTO_MAX);
			return;
		}

		/* Reserve space for headers */
		skb_reserve(skb, sk->sk_prot->max_header);
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
		dccp_transmit_skb(sk, skb);
	}
}

EXPORT_SYMBOL_GPL(dccp_send_ack);

#if 0
/* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
void dccp_send_delayed_ack(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	/*
	 * FIXME: tune this timer. elapsed time fixes the skew, so no problem
	 * with using 2s, and active senders also piggyback the ACK into a
	 * DATAACK packet, so this is really for quiescent senders.
	 */
	unsigned long timeout = jiffies + 2 * HZ;

	/* Use new timeout only if there wasn't a older one earlier. */
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 *
		 * FIXME: check the "about to expire" part
		 */
		if (icsk->icsk_ack.blocked) {
			dccp_send_ack(sk);
			return;
		}

		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
	}
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
}
#endif

void dccp_send_sync(struct sock *sk, const u64 ackno,
		    const enum dccp_pkt_type pkt_type)
{
	/*
	 * We are not putting this on the write queue, so
	 * dccp_transmit_skb() will set the ownership to this
	 * sock.
	 */
	struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);

	if (skb == NULL) {
		/* FIXME: how to make sure the sync is sent? */
		DCCP_CRIT("could not send %s", dccp_packet_name(pkt_type));
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
	DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;

	dccp_transmit_skb(sk, skb);
}

EXPORT_SYMBOL_GPL(dccp_send_sync);

/*
 * Send a DCCP_PKT_CLOSE/CLOSEREQ. The caller locks the socket for us. This
 * cannot be allowed to fail queueing a DCCP_PKT_CLOSE/CLOSEREQ frame under
 * any circumstances.
 */
void dccp_send_close(struct sock *sk, const int active)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;
	const gfp_t prio = active ? GFP_KERNEL : GFP_ATOMIC;

	skb = alloc_skb(sk->sk_prot->max_header, prio);
	if (skb == NULL)
		return;

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	if (dp->dccps_role == DCCP_ROLE_SERVER && !dp->dccps_server_timewait)
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSEREQ;
	else
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSE;

	if (active) {
		dccp_write_xmit(sk, 1);
		dccp_skb_entail(sk, skb);
		dccp_transmit_skb(sk, skb_clone(skb, prio));
		/*
		 * Retransmission timer for active-close: RFC 4340, 8.3 requires
		 * to retransmit the Close/CloseReq until the CLOSING/CLOSEREQ
		 * state can be left. The initial timeout is 2 RTTs.
		 * Since RTT measurement is done by the CCIDs, there is no easy
		 * way to get an RTT sample. The fallback RTT from RFC 4340, 3.4
		 * is too low (200ms); we use a high value to avoid unnecessary
		 * retransmissions when the link RTT is > 0.2 seconds.
		 * FIXME: Let main module sample RTTs and use that instead.
		 */
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
					  DCCP_TIMEOUT_INIT, DCCP_RTO_MAX);
	} else
		dccp_transmit_skb(sk, skb);
}