Initial import

1 files changed, 788 insertions, 0 deletions

diff --git a/net/sctp/output.c b/net/sctp/output.c
new file mode 100644
index 000000000..abe7c2db2
--- /dev/null
+++ b/net/sctp/output.c
@@ -0,0 +1,788 @@
+/* SCTP kernel implementation
+ * (C) Copyright IBM Corp. 2001, 2004
+ * Copyright (c) 1999-2000 Cisco, Inc.
+ * Copyright (c) 1999-2001 Motorola, Inc.
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * These functions handle output processing.
+ *
+ * This SCTP implementation 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, or (at your option)
+ * any later version.
+ *
+ * This SCTP implementation 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 GNU CC; see the file COPYING.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * Please send any bug reports or fixes you make to the
+ * email address(es):
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *    La Monte H.P. Yarroll <piggy@acm.org>
+ *    Karl Knutson          <karl@athena.chicago.il.us>
+ *    Jon Grimm             <jgrimm@austin.ibm.com>
+ *    Sridhar Samudrala     <sri@us.ibm.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/wait.h>
+#include <linux/time.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <net/inet_ecn.h>
+#include <net/ip.h>
+#include <net/icmp.h>
+#include <net/net_namespace.h>
+
+#include <linux/socket.h> /* for sa_family_t */
+#include <net/sock.h>
+
+#include <net/sctp/sctp.h>
+#include <net/sctp/sm.h>
+#include <net/sctp/checksum.h>
+
+/* Forward declarations for private helpers. */
+static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
+					      struct sctp_chunk *chunk);
+static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
+					   struct sctp_chunk *chunk);
+static void sctp_packet_append_data(struct sctp_packet *packet,
+					   struct sctp_chunk *chunk);
+static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
+					struct sctp_chunk *chunk,
+					u16 chunk_len);
+
+static void sctp_packet_reset(struct sctp_packet *packet)
+{
+	packet->size = packet->overhead;
+	packet->has_cookie_echo = 0;
+	packet->has_sack = 0;
+	packet->has_data = 0;
+	packet->has_auth = 0;
+	packet->ipfragok = 0;
+	packet->auth = NULL;
+}
+
+/* Config a packet.
+ * This appears to be a followup set of initializations.
+ */
+struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
+				       __u32 vtag, int ecn_capable)
+{
+	struct sctp_chunk *chunk = NULL;
+
+	pr_debug("%s: packet:%p vtag:0x%x\n", __func__, packet, vtag);
+
+	packet->vtag = vtag;
+
+	if (ecn_capable && sctp_packet_empty(packet)) {
+		chunk = sctp_get_ecne_prepend(packet->transport->asoc);
+
+		/* If there a is a prepend chunk stick it on the list before
+		 * any other chunks get appended.
+		 */
+		if (chunk)
+			sctp_packet_append_chunk(packet, chunk);
+	}
+
+	return packet;
+}
+
+/* Initialize the packet structure. */
+struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
+				     struct sctp_transport *transport,
+				     __u16 sport, __u16 dport)
+{
+	struct sctp_association *asoc = transport->asoc;
+	size_t overhead;
+
+	pr_debug("%s: packet:%p transport:%p\n", __func__, packet, transport);
+
+	packet->transport = transport;
+	packet->source_port = sport;
+	packet->destination_port = dport;
+	INIT_LIST_HEAD(&packet->chunk_list);
+	if (asoc) {
+		struct sctp_sock *sp = sctp_sk(asoc->base.sk);
+		overhead = sp->pf->af->net_header_len;
+	} else {
+		overhead = sizeof(struct ipv6hdr);
+	}
+	overhead += sizeof(struct sctphdr);
+	packet->overhead = overhead;
+	sctp_packet_reset(packet);
+	packet->vtag = 0;
+
+	return packet;
+}
+
+/* Free a packet.  */
+void sctp_packet_free(struct sctp_packet *packet)
+{
+	struct sctp_chunk *chunk, *tmp;
+
+	pr_debug("%s: packet:%p\n", __func__, packet);
+
+	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
+		list_del_init(&chunk->list);
+		sctp_chunk_free(chunk);
+	}
+}
+
+/* This routine tries to append the chunk to the offered packet. If adding
+ * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
+ * is not present in the packet, it transmits the input packet.
+ * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
+ * as it can fit in the packet, but any more data that does not fit in this
+ * packet can be sent only after receiving the COOKIE_ACK.
+ */
+sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
+				       struct sctp_chunk *chunk,
+				       int one_packet)
+{
+	sctp_xmit_t retval;
+	int error = 0;
+
+	pr_debug("%s: packet:%p chunk:%p\n", __func__, packet, chunk);
+
+	switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
+	case SCTP_XMIT_PMTU_FULL:
+		if (!packet->has_cookie_echo) {
+			error = sctp_packet_transmit(packet);
+			if (error < 0)
+				chunk->skb->sk->sk_err = -error;
+
+			/* If we have an empty packet, then we can NOT ever
+			 * return PMTU_FULL.
+			 */
+			if (!one_packet)
+				retval = sctp_packet_append_chunk(packet,
+								  chunk);
+		}
+		break;
+
+	case SCTP_XMIT_RWND_FULL:
+	case SCTP_XMIT_OK:
+	case SCTP_XMIT_DELAY:
+		break;
+	}
+
+	return retval;
+}
+
+/* Try to bundle an auth chunk into the packet. */
+static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
+					   struct sctp_chunk *chunk)
+{
+	struct sctp_association *asoc = pkt->transport->asoc;
+	struct sctp_chunk *auth;
+	sctp_xmit_t retval = SCTP_XMIT_OK;
+
+	/* if we don't have an association, we can't do authentication */
+	if (!asoc)
+		return retval;
+
+	/* See if this is an auth chunk we are bundling or if
+	 * auth is already bundled.
+	 */
+	if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
+		return retval;
+
+	/* if the peer did not request this chunk to be authenticated,
+	 * don't do it
+	 */
+	if (!chunk->auth)
+		return retval;
+
+	auth = sctp_make_auth(asoc);
+	if (!auth)
+		return retval;
+
+	retval = __sctp_packet_append_chunk(pkt, auth);
+
+	if (retval != SCTP_XMIT_OK)
+		sctp_chunk_free(auth);
+
+	return retval;
+}
+
+/* Try to bundle a SACK with the packet. */
+static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
+					   struct sctp_chunk *chunk)
+{
+	sctp_xmit_t retval = SCTP_XMIT_OK;
+
+	/* If sending DATA and haven't aleady bundled a SACK, try to
+	 * bundle one in to the packet.
+	 */
+	if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
+	    !pkt->has_cookie_echo) {
+		struct sctp_association *asoc;
+		struct timer_list *timer;
+		asoc = pkt->transport->asoc;
+		timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
+
+		/* If the SACK timer is running, we have a pending SACK */
+		if (timer_pending(timer)) {
+			struct sctp_chunk *sack;
+
+			if (pkt->transport->sack_generation !=
+			    pkt->transport->asoc->peer.sack_generation)
+				return retval;
+
+			asoc->a_rwnd = asoc->rwnd;
+			sack = sctp_make_sack(asoc);
+			if (sack) {
+				retval = __sctp_packet_append_chunk(pkt, sack);
+				if (retval != SCTP_XMIT_OK) {
+					sctp_chunk_free(sack);
+					goto out;
+				}
+				asoc->peer.sack_needed = 0;
+				if (del_timer(timer))
+					sctp_association_put(asoc);
+			}
+		}
+	}
+out:
+	return retval;
+}
+
+
+/* Append a chunk to the offered packet reporting back any inability to do
+ * so.
+ */
+static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
+					      struct sctp_chunk *chunk)
+{
+	sctp_xmit_t retval = SCTP_XMIT_OK;
+	__u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
+
+	/* Check to see if this chunk will fit into the packet */
+	retval = sctp_packet_will_fit(packet, chunk, chunk_len);
+	if (retval != SCTP_XMIT_OK)
+		goto finish;
+
+	/* We believe that this chunk is OK to add to the packet */
+	switch (chunk->chunk_hdr->type) {
+	case SCTP_CID_DATA:
+		/* Account for the data being in the packet */
+		sctp_packet_append_data(packet, chunk);
+		/* Disallow SACK bundling after DATA. */
+		packet->has_sack = 1;
+		/* Disallow AUTH bundling after DATA */
+		packet->has_auth = 1;
+		/* Let it be knows that packet has DATA in it */
+		packet->has_data = 1;
+		/* timestamp the chunk for rtx purposes */
+		chunk->sent_at = jiffies;
+		break;
+	case SCTP_CID_COOKIE_ECHO:
+		packet->has_cookie_echo = 1;
+		break;
+
+	case SCTP_CID_SACK:
+		packet->has_sack = 1;
+		if (chunk->asoc)
+			chunk->asoc->stats.osacks++;
+		break;
+
+	case SCTP_CID_AUTH:
+		packet->has_auth = 1;
+		packet->auth = chunk;
+		break;
+	}
+
+	/* It is OK to send this chunk.  */
+	list_add_tail(&chunk->list, &packet->chunk_list);
+	packet->size += chunk_len;
+	chunk->transport = packet->transport;
+finish:
+	return retval;
+}
+
+/* Append a chunk to the offered packet reporting back any inability to do
+ * so.
+ */
+sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
+				     struct sctp_chunk *chunk)
+{
+	sctp_xmit_t retval = SCTP_XMIT_OK;
+
+	pr_debug("%s: packet:%p chunk:%p\n", __func__, packet, chunk);
+
+	/* Data chunks are special.  Before seeing what else we can
+	 * bundle into this packet, check to see if we are allowed to
+	 * send this DATA.
+	 */
+	if (sctp_chunk_is_data(chunk)) {
+		retval = sctp_packet_can_append_data(packet, chunk);
+		if (retval != SCTP_XMIT_OK)
+			goto finish;
+	}
+
+	/* Try to bundle AUTH chunk */
+	retval = sctp_packet_bundle_auth(packet, chunk);
+	if (retval != SCTP_XMIT_OK)
+		goto finish;
+
+	/* Try to bundle SACK chunk */
+	retval = sctp_packet_bundle_sack(packet, chunk);
+	if (retval != SCTP_XMIT_OK)
+		goto finish;
+
+	retval = __sctp_packet_append_chunk(packet, chunk);
+
+finish:
+	return retval;
+}
+
+static void sctp_packet_release_owner(struct sk_buff *skb)
+{
+	sk_free(skb->sk);
+}
+
+static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
+{
+	skb_orphan(skb);
+	skb->sk = sk;
+	skb->destructor = sctp_packet_release_owner;
+
+	/*
+	 * The data chunks have already been accounted for in sctp_sendmsg(),
+	 * therefore only reserve a single byte to keep socket around until
+	 * the packet has been transmitted.
+	 */
+	atomic_inc(&sk->sk_wmem_alloc);
+}
+
+/* All packets are sent to the network through this function from
+ * sctp_outq_tail().
+ *
+ * The return value is a normal kernel error return value.
+ */
+int sctp_packet_transmit(struct sctp_packet *packet)
+{
+	struct sctp_transport *tp = packet->transport;
+	struct sctp_association *asoc = tp->asoc;
+	struct sctphdr *sh;
+	struct sk_buff *nskb;
+	struct sctp_chunk *chunk, *tmp;
+	struct sock *sk;
+	int err = 0;
+	int padding;		/* How much padding do we need?  */
+	__u8 has_data = 0;
+	struct dst_entry *dst;
+	unsigned char *auth = NULL;	/* pointer to auth in skb data */
+
+	pr_debug("%s: packet:%p\n", __func__, packet);
+
+	/* Do NOT generate a chunkless packet. */
+	if (list_empty(&packet->chunk_list))
+		return err;
+
+	/* Set up convenience variables... */
+	chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
+	sk = chunk->skb->sk;
+
+	/* Allocate the new skb.  */
+	nskb = alloc_skb(packet->size + MAX_HEADER, GFP_ATOMIC);
+	if (!nskb)
+		goto nomem;
+
+	/* Make sure the outbound skb has enough header room reserved. */
+	skb_reserve(nskb, packet->overhead + MAX_HEADER);
+
+	/* Set the owning socket so that we know where to get the
+	 * destination IP address.
+	 */
+	sctp_packet_set_owner_w(nskb, sk);
+
+	if (!sctp_transport_dst_check(tp)) {
+		sctp_transport_route(tp, NULL, sctp_sk(sk));
+		if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
+			sctp_assoc_sync_pmtu(sk, asoc);
+		}
+	}
+	dst = dst_clone(tp->dst);
+	if (!dst)
+		goto no_route;
+	skb_dst_set(nskb, dst);
+
+	/* Build the SCTP header.  */
+	sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
+	skb_reset_transport_header(nskb);
+	sh->source = htons(packet->source_port);
+	sh->dest   = htons(packet->destination_port);
+
+	/* From 6.8 Adler-32 Checksum Calculation:
+	 * After the packet is constructed (containing the SCTP common
+	 * header and one or more control or DATA chunks), the
+	 * transmitter shall:
+	 *
+	 * 1) Fill in the proper Verification Tag in the SCTP common
+	 *    header and initialize the checksum field to 0's.
+	 */
+	sh->vtag     = htonl(packet->vtag);
+	sh->checksum = 0;
+
+	/**
+	 * 6.10 Bundling
+	 *
+	 *    An endpoint bundles chunks by simply including multiple
+	 *    chunks in one outbound SCTP packet.  ...
+	 */
+
+	/**
+	 * 3.2  Chunk Field Descriptions
+	 *
+	 * The total length of a chunk (including Type, Length and
+	 * Value fields) MUST be a multiple of 4 bytes.  If the length
+	 * of the chunk is not a multiple of 4 bytes, the sender MUST
+	 * pad the chunk with all zero bytes and this padding is not
+	 * included in the chunk length field.  The sender should
+	 * never pad with more than 3 bytes.
+	 *
+	 * [This whole comment explains WORD_ROUND() below.]
+	 */
+
+	pr_debug("***sctp_transmit_packet***\n");
+
+	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
+		list_del_init(&chunk->list);
+		if (sctp_chunk_is_data(chunk)) {
+			/* 6.3.1 C4) When data is in flight and when allowed
+			 * by rule C5, a new RTT measurement MUST be made each
+			 * round trip.  Furthermore, new RTT measurements
+			 * SHOULD be made no more than once per round-trip
+			 * for a given destination transport address.
+			 */
+
+			if (!chunk->resent && !tp->rto_pending) {
+				chunk->rtt_in_progress = 1;
+				tp->rto_pending = 1;
+			}
+
+			has_data = 1;
+		}
+
+		padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
+		if (padding)
+			memset(skb_put(chunk->skb, padding), 0, padding);
+
+		/* if this is the auth chunk that we are adding,
+		 * store pointer where it will be added and put
+		 * the auth into the packet.
+		 */
+		if (chunk == packet->auth)
+			auth = skb_tail_pointer(nskb);
+
+		memcpy(skb_put(nskb, chunk->skb->len),
+			       chunk->skb->data, chunk->skb->len);
+
+		pr_debug("*** Chunk:%p[%s] %s 0x%x, length:%d, chunk->skb->len:%d, "
+			 "rtt_in_progress:%d\n", chunk,
+			 sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)),
+			 chunk->has_tsn ? "TSN" : "No TSN",
+			 chunk->has_tsn ? ntohl(chunk->subh.data_hdr->tsn) : 0,
+			 ntohs(chunk->chunk_hdr->length), chunk->skb->len,
+			 chunk->rtt_in_progress);
+
+		/*
+		 * If this is a control chunk, this is our last
+		 * reference. Free data chunks after they've been
+		 * acknowledged or have failed.
+		 */
+		if (!sctp_chunk_is_data(chunk))
+			sctp_chunk_free(chunk);
+	}
+
+	/* SCTP-AUTH, Section 6.2
+	 *    The sender MUST calculate the MAC as described in RFC2104 [2]
+	 *    using the hash function H as described by the MAC Identifier and
+	 *    the shared association key K based on the endpoint pair shared key
+	 *    described by the shared key identifier.  The 'data' used for the
+	 *    computation of the AUTH-chunk is given by the AUTH chunk with its
+	 *    HMAC field set to zero (as shown in Figure 6) followed by all
+	 *    chunks that are placed after the AUTH chunk in the SCTP packet.
+	 */
+	if (auth)
+		sctp_auth_calculate_hmac(asoc, nskb,
+					(struct sctp_auth_chunk *)auth,
+					GFP_ATOMIC);
+
+	/* 2) Calculate the Adler-32 checksum of the whole packet,
+	 *    including the SCTP common header and all the
+	 *    chunks.
+	 *
+	 * Note: Adler-32 is no longer applicable, as has been replaced
+	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
+	 */
+	if (!sctp_checksum_disable) {
+		if (!(dst->dev->features & NETIF_F_SCTP_CSUM) ||
+		    (dst_xfrm(dst) != NULL) || packet->ipfragok) {
+			sh->checksum = sctp_compute_cksum(nskb, 0);
+		} else {
+			/* no need to seed pseudo checksum for SCTP */
+			nskb->ip_summed = CHECKSUM_PARTIAL;
+			nskb->csum_start = skb_transport_header(nskb) - nskb->head;
+			nskb->csum_offset = offsetof(struct sctphdr, checksum);
+		}
+	}
+
+	/* IP layer ECN support
+	 * From RFC 2481
+	 *  "The ECN-Capable Transport (ECT) bit would be set by the
+	 *   data sender to indicate that the end-points of the
+	 *   transport protocol are ECN-capable."
+	 *
+	 * Now setting the ECT bit all the time, as it should not cause
+	 * any problems protocol-wise even if our peer ignores it.
+	 *
+	 * Note: The works for IPv6 layer checks this bit too later
+	 * in transmission.  See IP6_ECN_flow_xmit().
+	 */
+	tp->af_specific->ecn_capable(nskb->sk);
+
+	/* Set up the IP options.  */
+	/* BUG: not implemented
+	 * For v4 this all lives somewhere in sk->sk_opt...
+	 */
+
+	/* Dump that on IP!  */
+	if (asoc) {
+		asoc->stats.opackets++;
+		if (asoc->peer.last_sent_to != tp)
+			/* Considering the multiple CPU scenario, this is a
+			 * "correcter" place for last_sent_to.  --xguo
+			 */
+			asoc->peer.last_sent_to = tp;
+	}
+
+	if (has_data) {
+		struct timer_list *timer;
+		unsigned long timeout;
+
+		/* Restart the AUTOCLOSE timer when sending data. */
+		if (sctp_state(asoc, ESTABLISHED) &&
+		    asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE]) {
+			timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
+			timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
+
+			if (!mod_timer(timer, jiffies + timeout))
+				sctp_association_hold(asoc);
+		}
+	}
+
+	pr_debug("***sctp_transmit_packet*** skb->len:%d\n", nskb->len);
+
+	nskb->ignore_df = packet->ipfragok;
+	tp->af_specific->sctp_xmit(nskb, tp);
+
+out:
+	sctp_packet_reset(packet);
+	return err;
+no_route:
+	kfree_skb(nskb);
+
+	if (asoc)
+		IP_INC_STATS(sock_net(asoc->base.sk), IPSTATS_MIB_OUTNOROUTES);
+
+	/* FIXME: Returning the 'err' will effect all the associations
+	 * associated with a socket, although only one of the paths of the
+	 * association is unreachable.
+	 * The real failure of a transport or association can be passed on
+	 * to the user via notifications. So setting this error may not be
+	 * required.
+	 */
+	 /* err = -EHOSTUNREACH; */
+err:
+	/* Control chunks are unreliable so just drop them.  DATA chunks
+	 * will get resent or dropped later.
+	 */
+
+	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
+		list_del_init(&chunk->list);
+		if (!sctp_chunk_is_data(chunk))
+			sctp_chunk_free(chunk);
+	}
+	goto out;
+nomem:
+	err = -ENOMEM;
+	goto err;
+}
+
+/********************************************************************
+ * 2nd Level Abstractions
+ ********************************************************************/
+
+/* This private function check to see if a chunk can be added */
+static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
+					   struct sctp_chunk *chunk)
+{
+	size_t datasize, rwnd, inflight, flight_size;
+	struct sctp_transport *transport = packet->transport;
+	struct sctp_association *asoc = transport->asoc;
+	struct sctp_outq *q = &asoc->outqueue;
+
+	/* RFC 2960 6.1  Transmission of DATA Chunks
+	 *
+	 * A) At any given time, the data sender MUST NOT transmit new data to
+	 * any destination transport address if its peer's rwnd indicates
+	 * that the peer has no buffer space (i.e. rwnd is 0, see Section
+	 * 6.2.1).  However, regardless of the value of rwnd (including if it
+	 * is 0), the data sender can always have one DATA chunk in flight to
+	 * the receiver if allowed by cwnd (see rule B below).  This rule
+	 * allows the sender to probe for a change in rwnd that the sender
+	 * missed due to the SACK having been lost in transit from the data
+	 * receiver to the data sender.
+	 */
+
+	rwnd = asoc->peer.rwnd;
+	inflight = q->outstanding_bytes;
+	flight_size = transport->flight_size;
+
+	datasize = sctp_data_size(chunk);
+
+	if (datasize > rwnd && inflight > 0)
+		/* We have (at least) one data chunk in flight,
+		 * so we can't fall back to rule 6.1 B).
+		 */
+		return SCTP_XMIT_RWND_FULL;
+
+	/* RFC 2960 6.1  Transmission of DATA Chunks
+	 *
+	 * B) At any given time, the sender MUST NOT transmit new data
+	 * to a given transport address if it has cwnd or more bytes
+	 * of data outstanding to that transport address.
+	 */
+	/* RFC 7.2.4 & the Implementers Guide 2.8.
+	 *
+	 * 3) ...
+	 *    When a Fast Retransmit is being performed the sender SHOULD
+	 *    ignore the value of cwnd and SHOULD NOT delay retransmission.
+	 */
+	if (chunk->fast_retransmit != SCTP_NEED_FRTX &&
+	    flight_size >= transport->cwnd)
+		return SCTP_XMIT_RWND_FULL;
+
+	/* Nagle's algorithm to solve small-packet problem:
+	 * Inhibit the sending of new chunks when new outgoing data arrives
+	 * if any previously transmitted data on the connection remains
+	 * unacknowledged.
+	 */
+
+	if (sctp_sk(asoc->base.sk)->nodelay)
+		/* Nagle disabled */
+		return SCTP_XMIT_OK;
+
+	if (!sctp_packet_empty(packet))
+		/* Append to packet */
+		return SCTP_XMIT_OK;
+
+	if (inflight == 0)
+		/* Nothing unacked */
+		return SCTP_XMIT_OK;
+
+	if (!sctp_state(asoc, ESTABLISHED))
+		return SCTP_XMIT_OK;
+
+	/* Check whether this chunk and all the rest of pending data will fit
+	 * or delay in hopes of bundling a full sized packet.
+	 */
+	if (chunk->skb->len + q->out_qlen >= transport->pathmtu - packet->overhead)
+		/* Enough data queued to fill a packet */
+		return SCTP_XMIT_OK;
+
+	/* Don't delay large message writes that may have been fragmented */
+	if (!chunk->msg->can_delay)
+		return SCTP_XMIT_OK;
+
+	/* Defer until all data acked or packet full */
+	return SCTP_XMIT_DELAY;
+}
+
+/* This private function does management things when adding DATA chunk */
+static void sctp_packet_append_data(struct sctp_packet *packet,
+				struct sctp_chunk *chunk)
+{
+	struct sctp_transport *transport = packet->transport;
+	size_t datasize = sctp_data_size(chunk);
+	struct sctp_association *asoc = transport->asoc;
+	u32 rwnd = asoc->peer.rwnd;
+
+	/* Keep track of how many bytes are in flight over this transport. */
+	transport->flight_size += datasize;
+
+	/* Keep track of how many bytes are in flight to the receiver. */
+	asoc->outqueue.outstanding_bytes += datasize;
+
+	/* Update our view of the receiver's rwnd. */
+	if (datasize < rwnd)
+		rwnd -= datasize;
+	else
+		rwnd = 0;
+
+	asoc->peer.rwnd = rwnd;
+	/* Has been accepted for transmission. */
+	if (!asoc->peer.prsctp_capable)
+		chunk->msg->can_abandon = 0;
+	sctp_chunk_assign_tsn(chunk);
+	sctp_chunk_assign_ssn(chunk);
+}
+
+static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
+					struct sctp_chunk *chunk,
+					u16 chunk_len)
+{
+	size_t psize;
+	size_t pmtu;
+	int too_big;
+	sctp_xmit_t retval = SCTP_XMIT_OK;
+
+	psize = packet->size;
+	pmtu  = ((packet->transport->asoc) ?
+		(packet->transport->asoc->pathmtu) :
+		(packet->transport->pathmtu));
+
+	too_big = (psize + chunk_len > pmtu);
+
+	/* Decide if we need to fragment or resubmit later. */
+	if (too_big) {
+		/* It's OK to fragmet at IP level if any one of the following
+		 * is true:
+		 * 	1. The packet is empty (meaning this chunk is greater
+		 * 	   the MTU)
+		 * 	2. The chunk we are adding is a control chunk
+		 * 	3. The packet doesn't have any data in it yet and data
+		 * 	requires authentication.
+		 */
+		if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
+		    (!packet->has_data && chunk->auth)) {
+			/* We no longer do re-fragmentation.
+			 * Just fragment at the IP layer, if we
+			 * actually hit this condition
+			 */
+			packet->ipfragok = 1;
+		} else {
+			retval = SCTP_XMIT_PMTU_FULL;
+		}
+	}
+
+	return retval;
+}