usb-storage: clean up unusual_devs.h
[linux-2.6/mini2440.git] / net / sctp / output.c
blobc3f417f7ec6e8d305ae3e50ef7aa15fd33170080
1 /* SCTP kernel implementation
2 * (C) Copyright IBM Corp. 2001, 2004
3 * Copyright (c) 1999-2000 Cisco, Inc.
4 * Copyright (c) 1999-2001 Motorola, Inc.
6 * This file is part of the SCTP kernel implementation
8 * These functions handle output processing.
10 * This SCTP implementation is free software;
11 * you can redistribute it and/or modify it under the terms of
12 * the GNU General Public License as published by
13 * the Free Software Foundation; either version 2, or (at your option)
14 * any later version.
16 * This SCTP implementation is distributed in the hope that it
17 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
18 * ************************
19 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
20 * See the GNU General Public License for more details.
22 * You should have received a copy of the GNU General Public License
23 * along with GNU CC; see the file COPYING. If not, write to
24 * the Free Software Foundation, 59 Temple Place - Suite 330,
25 * Boston, MA 02111-1307, USA.
27 * Please send any bug reports or fixes you make to the
28 * email address(es):
29 * lksctp developers <lksctp-developers@lists.sourceforge.net>
31 * Or submit a bug report through the following website:
32 * http://www.sf.net/projects/lksctp
34 * Written or modified by:
35 * La Monte H.P. Yarroll <piggy@acm.org>
36 * Karl Knutson <karl@athena.chicago.il.us>
37 * Jon Grimm <jgrimm@austin.ibm.com>
38 * Sridhar Samudrala <sri@us.ibm.com>
40 * Any bugs reported given to us we will try to fix... any fixes shared will
41 * be incorporated into the next SCTP release.
44 #include <linux/types.h>
45 #include <linux/kernel.h>
46 #include <linux/wait.h>
47 #include <linux/time.h>
48 #include <linux/ip.h>
49 #include <linux/ipv6.h>
50 #include <linux/init.h>
51 #include <net/inet_ecn.h>
52 #include <net/icmp.h>
53 #include <net/net_namespace.h>
55 #ifndef TEST_FRAME
56 #include <net/tcp.h>
57 #endif /* TEST_FRAME (not defined) */
59 #include <linux/socket.h> /* for sa_family_t */
60 #include <net/sock.h>
62 #include <net/sctp/sctp.h>
63 #include <net/sctp/sm.h>
64 #include <net/sctp/checksum.h>
66 /* Forward declarations for private helpers. */
67 static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
68 struct sctp_chunk *chunk);
70 /* Config a packet.
71 * This appears to be a followup set of initializations.
73 struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
74 __u32 vtag, int ecn_capable)
76 struct sctp_chunk *chunk = NULL;
78 SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
79 packet, vtag);
81 packet->vtag = vtag;
82 packet->has_cookie_echo = 0;
83 packet->has_sack = 0;
84 packet->has_auth = 0;
85 packet->has_data = 0;
86 packet->ipfragok = 0;
87 packet->auth = NULL;
89 if (ecn_capable && sctp_packet_empty(packet)) {
90 chunk = sctp_get_ecne_prepend(packet->transport->asoc);
92 /* If there a is a prepend chunk stick it on the list before
93 * any other chunks get appended.
95 if (chunk)
96 sctp_packet_append_chunk(packet, chunk);
99 return packet;
102 /* Initialize the packet structure. */
103 struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
104 struct sctp_transport *transport,
105 __u16 sport, __u16 dport)
107 struct sctp_association *asoc = transport->asoc;
108 size_t overhead;
110 SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
111 packet, transport);
113 packet->transport = transport;
114 packet->source_port = sport;
115 packet->destination_port = dport;
116 INIT_LIST_HEAD(&packet->chunk_list);
117 if (asoc) {
118 struct sctp_sock *sp = sctp_sk(asoc->base.sk);
119 overhead = sp->pf->af->net_header_len;
120 } else {
121 overhead = sizeof(struct ipv6hdr);
123 overhead += sizeof(struct sctphdr);
124 packet->overhead = overhead;
125 packet->size = overhead;
126 packet->vtag = 0;
127 packet->has_cookie_echo = 0;
128 packet->has_sack = 0;
129 packet->has_auth = 0;
130 packet->has_data = 0;
131 packet->ipfragok = 0;
132 packet->malloced = 0;
133 packet->auth = NULL;
134 return packet;
137 /* Free a packet. */
138 void sctp_packet_free(struct sctp_packet *packet)
140 struct sctp_chunk *chunk, *tmp;
142 SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
144 list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
145 list_del_init(&chunk->list);
146 sctp_chunk_free(chunk);
149 if (packet->malloced)
150 kfree(packet);
153 /* This routine tries to append the chunk to the offered packet. If adding
154 * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
155 * is not present in the packet, it transmits the input packet.
156 * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
157 * as it can fit in the packet, but any more data that does not fit in this
158 * packet can be sent only after receiving the COOKIE_ACK.
160 sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
161 struct sctp_chunk *chunk,
162 int one_packet)
164 sctp_xmit_t retval;
165 int error = 0;
167 SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
168 packet, chunk);
170 switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
171 case SCTP_XMIT_PMTU_FULL:
172 if (!packet->has_cookie_echo) {
173 error = sctp_packet_transmit(packet);
174 if (error < 0)
175 chunk->skb->sk->sk_err = -error;
177 /* If we have an empty packet, then we can NOT ever
178 * return PMTU_FULL.
180 if (!one_packet)
181 retval = sctp_packet_append_chunk(packet,
182 chunk);
184 break;
186 case SCTP_XMIT_RWND_FULL:
187 case SCTP_XMIT_OK:
188 case SCTP_XMIT_NAGLE_DELAY:
189 break;
192 return retval;
195 /* Try to bundle an auth chunk into the packet. */
196 static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
197 struct sctp_chunk *chunk)
199 struct sctp_association *asoc = pkt->transport->asoc;
200 struct sctp_chunk *auth;
201 sctp_xmit_t retval = SCTP_XMIT_OK;
203 /* if we don't have an association, we can't do authentication */
204 if (!asoc)
205 return retval;
207 /* See if this is an auth chunk we are bundling or if
208 * auth is already bundled.
210 if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->auth)
211 return retval;
213 /* if the peer did not request this chunk to be authenticated,
214 * don't do it
216 if (!chunk->auth)
217 return retval;
219 auth = sctp_make_auth(asoc);
220 if (!auth)
221 return retval;
223 retval = sctp_packet_append_chunk(pkt, auth);
225 return retval;
228 /* Try to bundle a SACK with the packet. */
229 static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
230 struct sctp_chunk *chunk)
232 sctp_xmit_t retval = SCTP_XMIT_OK;
234 /* If sending DATA and haven't aleady bundled a SACK, try to
235 * bundle one in to the packet.
237 if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
238 !pkt->has_cookie_echo) {
239 struct sctp_association *asoc;
240 asoc = pkt->transport->asoc;
242 if (asoc->a_rwnd > asoc->rwnd) {
243 struct sctp_chunk *sack;
244 asoc->a_rwnd = asoc->rwnd;
245 sack = sctp_make_sack(asoc);
246 if (sack) {
247 struct timer_list *timer;
248 retval = sctp_packet_append_chunk(pkt, sack);
249 asoc->peer.sack_needed = 0;
250 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
251 if (timer_pending(timer) && del_timer(timer))
252 sctp_association_put(asoc);
256 return retval;
259 /* Append a chunk to the offered packet reporting back any inability to do
260 * so.
262 sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
263 struct sctp_chunk *chunk)
265 sctp_xmit_t retval = SCTP_XMIT_OK;
266 __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
267 size_t psize;
268 size_t pmtu;
269 int too_big;
271 SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
272 chunk);
274 /* Try to bundle AUTH chunk */
275 retval = sctp_packet_bundle_auth(packet, chunk);
276 if (retval != SCTP_XMIT_OK)
277 goto finish;
279 /* Try to bundle SACK chunk */
280 retval = sctp_packet_bundle_sack(packet, chunk);
281 if (retval != SCTP_XMIT_OK)
282 goto finish;
284 psize = packet->size;
285 pmtu = ((packet->transport->asoc) ?
286 (packet->transport->asoc->pathmtu) :
287 (packet->transport->pathmtu));
289 too_big = (psize + chunk_len > pmtu);
291 /* Decide if we need to fragment or resubmit later. */
292 if (too_big) {
293 /* It's OK to fragmet at IP level if any one of the following
294 * is true:
295 * 1. The packet is empty (meaning this chunk is greater
296 * the MTU)
297 * 2. The chunk we are adding is a control chunk
298 * 3. The packet doesn't have any data in it yet and data
299 * requires authentication.
301 if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
302 (!packet->has_data && chunk->auth)) {
303 /* We no longer do re-fragmentation.
304 * Just fragment at the IP layer, if we
305 * actually hit this condition
307 packet->ipfragok = 1;
308 goto append;
310 } else {
311 retval = SCTP_XMIT_PMTU_FULL;
312 goto finish;
316 append:
317 /* We believe that this chunk is OK to add to the packet (as
318 * long as we have the cwnd for it).
321 /* DATA is a special case since we must examine both rwnd and cwnd
322 * before we send DATA.
324 switch (chunk->chunk_hdr->type) {
325 case SCTP_CID_DATA:
326 retval = sctp_packet_append_data(packet, chunk);
327 /* Disallow SACK bundling after DATA. */
328 packet->has_sack = 1;
329 /* Disallow AUTH bundling after DATA */
330 packet->has_auth = 1;
331 /* Let it be knows that packet has DATA in it */
332 packet->has_data = 1;
333 if (SCTP_XMIT_OK != retval)
334 goto finish;
335 break;
336 case SCTP_CID_COOKIE_ECHO:
337 packet->has_cookie_echo = 1;
338 break;
340 case SCTP_CID_SACK:
341 packet->has_sack = 1;
342 break;
344 case SCTP_CID_AUTH:
345 packet->has_auth = 1;
346 packet->auth = chunk;
347 break;
350 /* It is OK to send this chunk. */
351 list_add_tail(&chunk->list, &packet->chunk_list);
352 packet->size += chunk_len;
353 chunk->transport = packet->transport;
354 finish:
355 return retval;
358 /* All packets are sent to the network through this function from
359 * sctp_outq_tail().
361 * The return value is a normal kernel error return value.
363 int sctp_packet_transmit(struct sctp_packet *packet)
365 struct sctp_transport *tp = packet->transport;
366 struct sctp_association *asoc = tp->asoc;
367 struct sctphdr *sh;
368 __be32 crc32 = __constant_cpu_to_be32(0);
369 struct sk_buff *nskb;
370 struct sctp_chunk *chunk, *tmp;
371 struct sock *sk;
372 int err = 0;
373 int padding; /* How much padding do we need? */
374 __u8 has_data = 0;
375 struct dst_entry *dst = tp->dst;
376 unsigned char *auth = NULL; /* pointer to auth in skb data */
377 __u32 cksum_buf_len = sizeof(struct sctphdr);
379 SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
381 /* Do NOT generate a chunkless packet. */
382 if (list_empty(&packet->chunk_list))
383 return err;
385 /* Set up convenience variables... */
386 chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
387 sk = chunk->skb->sk;
389 /* Allocate the new skb. */
390 nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
391 if (!nskb)
392 goto nomem;
394 /* Make sure the outbound skb has enough header room reserved. */
395 skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
397 /* Set the owning socket so that we know where to get the
398 * destination IP address.
400 skb_set_owner_w(nskb, sk);
402 /* The 'obsolete' field of dst is set to 2 when a dst is freed. */
403 if (!dst || (dst->obsolete > 1)) {
404 dst_release(dst);
405 sctp_transport_route(tp, NULL, sctp_sk(sk));
406 if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
407 sctp_assoc_sync_pmtu(asoc);
410 nskb->dst = dst_clone(tp->dst);
411 if (!nskb->dst)
412 goto no_route;
413 dst = nskb->dst;
415 /* Build the SCTP header. */
416 sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
417 sh->source = htons(packet->source_port);
418 sh->dest = htons(packet->destination_port);
420 /* From 6.8 Adler-32 Checksum Calculation:
421 * After the packet is constructed (containing the SCTP common
422 * header and one or more control or DATA chunks), the
423 * transmitter shall:
425 * 1) Fill in the proper Verification Tag in the SCTP common
426 * header and initialize the checksum field to 0's.
428 sh->vtag = htonl(packet->vtag);
429 sh->checksum = 0;
432 * 6.10 Bundling
434 * An endpoint bundles chunks by simply including multiple
435 * chunks in one outbound SCTP packet. ...
439 * 3.2 Chunk Field Descriptions
441 * The total length of a chunk (including Type, Length and
442 * Value fields) MUST be a multiple of 4 bytes. If the length
443 * of the chunk is not a multiple of 4 bytes, the sender MUST
444 * pad the chunk with all zero bytes and this padding is not
445 * included in the chunk length field. The sender should
446 * never pad with more than 3 bytes.
448 * [This whole comment explains WORD_ROUND() below.]
450 SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
451 list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
452 list_del_init(&chunk->list);
453 if (sctp_chunk_is_data(chunk)) {
455 if (!chunk->has_tsn) {
456 sctp_chunk_assign_ssn(chunk);
457 sctp_chunk_assign_tsn(chunk);
459 /* 6.3.1 C4) When data is in flight and when allowed
460 * by rule C5, a new RTT measurement MUST be made each
461 * round trip. Furthermore, new RTT measurements
462 * SHOULD be made no more than once per round-trip
463 * for a given destination transport address.
466 if (!tp->rto_pending) {
467 chunk->rtt_in_progress = 1;
468 tp->rto_pending = 1;
470 } else
471 chunk->resent = 1;
473 chunk->sent_at = jiffies;
474 has_data = 1;
477 padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
478 if (padding)
479 memset(skb_put(chunk->skb, padding), 0, padding);
481 /* if this is the auth chunk that we are adding,
482 * store pointer where it will be added and put
483 * the auth into the packet.
485 if (chunk == packet->auth)
486 auth = skb_tail_pointer(nskb);
488 cksum_buf_len += chunk->skb->len;
489 memcpy(skb_put(nskb, chunk->skb->len),
490 chunk->skb->data, chunk->skb->len);
492 SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
493 "*** Chunk", chunk,
494 sctp_cname(SCTP_ST_CHUNK(
495 chunk->chunk_hdr->type)),
496 chunk->has_tsn ? "TSN" : "No TSN",
497 chunk->has_tsn ?
498 ntohl(chunk->subh.data_hdr->tsn) : 0,
499 "length", ntohs(chunk->chunk_hdr->length),
500 "chunk->skb->len", chunk->skb->len,
501 "rtt_in_progress", chunk->rtt_in_progress);
504 * If this is a control chunk, this is our last
505 * reference. Free data chunks after they've been
506 * acknowledged or have failed.
508 if (!sctp_chunk_is_data(chunk))
509 sctp_chunk_free(chunk);
512 /* SCTP-AUTH, Section 6.2
513 * The sender MUST calculate the MAC as described in RFC2104 [2]
514 * using the hash function H as described by the MAC Identifier and
515 * the shared association key K based on the endpoint pair shared key
516 * described by the shared key identifier. The 'data' used for the
517 * computation of the AUTH-chunk is given by the AUTH chunk with its
518 * HMAC field set to zero (as shown in Figure 6) followed by all
519 * chunks that are placed after the AUTH chunk in the SCTP packet.
521 if (auth)
522 sctp_auth_calculate_hmac(asoc, nskb,
523 (struct sctp_auth_chunk *)auth,
524 GFP_ATOMIC);
526 /* 2) Calculate the Adler-32 checksum of the whole packet,
527 * including the SCTP common header and all the
528 * chunks.
530 * Note: Adler-32 is no longer applicable, as has been replaced
531 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
533 if (!(dst->dev->features & NETIF_F_NO_CSUM)) {
534 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
535 crc32 = sctp_end_cksum(crc32);
536 } else
537 nskb->ip_summed = CHECKSUM_UNNECESSARY;
539 /* 3) Put the resultant value into the checksum field in the
540 * common header, and leave the rest of the bits unchanged.
542 sh->checksum = crc32;
544 /* IP layer ECN support
545 * From RFC 2481
546 * "The ECN-Capable Transport (ECT) bit would be set by the
547 * data sender to indicate that the end-points of the
548 * transport protocol are ECN-capable."
550 * Now setting the ECT bit all the time, as it should not cause
551 * any problems protocol-wise even if our peer ignores it.
553 * Note: The works for IPv6 layer checks this bit too later
554 * in transmission. See IP6_ECN_flow_xmit().
556 (*tp->af_specific->ecn_capable)(nskb->sk);
558 /* Set up the IP options. */
559 /* BUG: not implemented
560 * For v4 this all lives somewhere in sk->sk_opt...
563 /* Dump that on IP! */
564 if (asoc && asoc->peer.last_sent_to != tp) {
565 /* Considering the multiple CPU scenario, this is a
566 * "correcter" place for last_sent_to. --xguo
568 asoc->peer.last_sent_to = tp;
571 if (has_data) {
572 struct timer_list *timer;
573 unsigned long timeout;
575 tp->last_time_used = jiffies;
577 /* Restart the AUTOCLOSE timer when sending data. */
578 if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
579 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
580 timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
582 if (!mod_timer(timer, jiffies + timeout))
583 sctp_association_hold(asoc);
587 SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
588 nskb->len);
590 nskb->local_df = packet->ipfragok;
591 (*tp->af_specific->sctp_xmit)(nskb, tp);
593 out:
594 packet->size = packet->overhead;
595 return err;
596 no_route:
597 kfree_skb(nskb);
598 IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
600 /* FIXME: Returning the 'err' will effect all the associations
601 * associated with a socket, although only one of the paths of the
602 * association is unreachable.
603 * The real failure of a transport or association can be passed on
604 * to the user via notifications. So setting this error may not be
605 * required.
607 /* err = -EHOSTUNREACH; */
608 err:
609 /* Control chunks are unreliable so just drop them. DATA chunks
610 * will get resent or dropped later.
613 list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
614 list_del_init(&chunk->list);
615 if (!sctp_chunk_is_data(chunk))
616 sctp_chunk_free(chunk);
618 goto out;
619 nomem:
620 err = -ENOMEM;
621 goto err;
624 /********************************************************************
625 * 2nd Level Abstractions
626 ********************************************************************/
628 /* This private function handles the specifics of appending DATA chunks. */
629 static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
630 struct sctp_chunk *chunk)
632 sctp_xmit_t retval = SCTP_XMIT_OK;
633 size_t datasize, rwnd, inflight;
634 struct sctp_transport *transport = packet->transport;
635 __u32 max_burst_bytes;
636 struct sctp_association *asoc = transport->asoc;
637 struct sctp_sock *sp = sctp_sk(asoc->base.sk);
638 struct sctp_outq *q = &asoc->outqueue;
640 /* RFC 2960 6.1 Transmission of DATA Chunks
642 * A) At any given time, the data sender MUST NOT transmit new data to
643 * any destination transport address if its peer's rwnd indicates
644 * that the peer has no buffer space (i.e. rwnd is 0, see Section
645 * 6.2.1). However, regardless of the value of rwnd (including if it
646 * is 0), the data sender can always have one DATA chunk in flight to
647 * the receiver if allowed by cwnd (see rule B below). This rule
648 * allows the sender to probe for a change in rwnd that the sender
649 * missed due to the SACK having been lost in transit from the data
650 * receiver to the data sender.
653 rwnd = asoc->peer.rwnd;
654 inflight = asoc->outqueue.outstanding_bytes;
656 datasize = sctp_data_size(chunk);
658 if (datasize > rwnd) {
659 if (inflight > 0) {
660 /* We have (at least) one data chunk in flight,
661 * so we can't fall back to rule 6.1 B).
663 retval = SCTP_XMIT_RWND_FULL;
664 goto finish;
668 /* sctpimpguide-05 2.14.2
669 * D) When the time comes for the sender to
670 * transmit new DATA chunks, the protocol parameter Max.Burst MUST
671 * first be applied to limit how many new DATA chunks may be sent.
672 * The limit is applied by adjusting cwnd as follows:
673 * if ((flightsize + Max.Burst * MTU) < cwnd)
674 * cwnd = flightsize + Max.Burst * MTU
676 max_burst_bytes = asoc->max_burst * asoc->pathmtu;
677 if ((transport->flight_size + max_burst_bytes) < transport->cwnd) {
678 transport->cwnd = transport->flight_size + max_burst_bytes;
679 SCTP_DEBUG_PRINTK("%s: cwnd limited by max_burst: "
680 "transport: %p, cwnd: %d, "
681 "ssthresh: %d, flight_size: %d, "
682 "pba: %d\n",
683 __func__, transport,
684 transport->cwnd,
685 transport->ssthresh,
686 transport->flight_size,
687 transport->partial_bytes_acked);
690 /* RFC 2960 6.1 Transmission of DATA Chunks
692 * B) At any given time, the sender MUST NOT transmit new data
693 * to a given transport address if it has cwnd or more bytes
694 * of data outstanding to that transport address.
696 /* RFC 7.2.4 & the Implementers Guide 2.8.
698 * 3) ...
699 * When a Fast Retransmit is being performed the sender SHOULD
700 * ignore the value of cwnd and SHOULD NOT delay retransmission.
702 if (chunk->fast_retransmit != SCTP_NEED_FRTX)
703 if (transport->flight_size >= transport->cwnd) {
704 retval = SCTP_XMIT_RWND_FULL;
705 goto finish;
708 /* Nagle's algorithm to solve small-packet problem:
709 * Inhibit the sending of new chunks when new outgoing data arrives
710 * if any previously transmitted data on the connection remains
711 * unacknowledged.
713 if (!sp->nodelay && sctp_packet_empty(packet) &&
714 q->outstanding_bytes && sctp_state(asoc, ESTABLISHED)) {
715 unsigned len = datasize + q->out_qlen;
717 /* Check whether this chunk and all the rest of pending
718 * data will fit or delay in hopes of bundling a full
719 * sized packet.
721 if (len < asoc->frag_point) {
722 retval = SCTP_XMIT_NAGLE_DELAY;
723 goto finish;
727 /* Keep track of how many bytes are in flight over this transport. */
728 transport->flight_size += datasize;
730 /* Keep track of how many bytes are in flight to the receiver. */
731 asoc->outqueue.outstanding_bytes += datasize;
733 /* Update our view of the receiver's rwnd. Include sk_buff overhead
734 * while updating peer.rwnd so that it reduces the chances of a
735 * receiver running out of receive buffer space even when receive
736 * window is still open. This can happen when a sender is sending
737 * sending small messages.
739 datasize += sizeof(struct sk_buff);
740 if (datasize < rwnd)
741 rwnd -= datasize;
742 else
743 rwnd = 0;
745 asoc->peer.rwnd = rwnd;
746 /* Has been accepted for transmission. */
747 if (!asoc->peer.prsctp_capable)
748 chunk->msg->can_abandon = 0;
750 finish:
751 return retval;