sctp: introduce stream scheduler foundations

This patch introduces the hooks necessary to do stream scheduling, as
per RFC Draft ndata.  It also introduces the first scheduler, which is
what we do today but now factored out: first come first served (FCFS).

With stream scheduling now we have to track which chunk was enqueued on
which stream and be able to select another other than the in front of
the main outqueue. So we introduce a list on sctp_stream_out_ext
structure for this purpose.

We reuse sctp_chunk->transmitted_list space for the list above, as the
chunk cannot belong to the two lists at the same time. By using the
union in there, we can have distinct names for these moments.

sctp_sched_ops are the operations expected to be implemented by each
scheduler. The dequeueing is a bit particular to this implementation but
it is to match how we dequeue packets today. We first dequeue and then
check if it fits the packet and if not, we requeue it at head. Thus why
we don't have a peek operation but have dequeue_done instead, which is
called once the chunk can be safely considered as transmitted.

The check removed from sctp_outq_flush is now performed by
sctp_stream_outq_migrate, which is only called during assoc setup.
(sctp_sendmsg() also checks for it)

The only operation that is foreseen but not yet added here is a way to
signalize that a new packet is starting or that the packet is done, for
round robin scheduler per packet, but is intentionally left to the
patch that actually implements it.

Support for I-DATA chunks, also described in this RFC, with user message
interleaving is straightforward as it just requires the schedulers to
probe for the feature and ignore datamsg boundaries when dequeueing.

See-also: https://tools.ietf.org/html/draft-ietf-tsvwg-sctp-ndata-13Tested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/stream_sched.h

+/* SCTP kernel implementation
+ * (C) Copyright Red Hat Inc. 2017
+ *
+ * These are definitions used by the stream schedulers, defined in RFC
+ * draft ndata (https://tools.ietf.org/html/draft-ietf-tsvwg-sctp-ndata-11)
+ *
+ * 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 addresses:
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *   Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
+ */
+
+#ifndef __sctp_stream_sched_h__
+#define __sctp_stream_sched_h__
+
+struct sctp_sched_ops {
+	/* Property handling for a given stream */
+	int (*set)(struct sctp_stream *stream, __u16 sid, __u16 value,
+		   gfp_t gfp);
+	int (*get)(struct sctp_stream *stream, __u16 sid, __u16 *value);
+
+	/* Init the specific scheduler */
+	int (*init)(struct sctp_stream *stream);
+	/* Init a stream */
+	int (*init_sid)(struct sctp_stream *stream, __u16 sid, gfp_t gfp);
+	/* Frees the entire thing */
+	void (*free)(struct sctp_stream *stream);
+
+	/* Enqueue a chunk */
+	void (*enqueue)(struct sctp_outq *q, struct sctp_datamsg *msg);
+	/* Dequeue a chunk */
+	struct sctp_chunk *(*dequeue)(struct sctp_outq *q);
+	/* Called only if the chunk fit the packet */
+	void (*dequeue_done)(struct sctp_outq *q, struct sctp_chunk *chunk);
+	/* Sched all chunks already enqueued */
+	void (*sched_all)(struct sctp_stream *steam);
+	/* Unched all chunks already enqueued */
+	void (*unsched_all)(struct sctp_stream *steam);
+};
+
+int sctp_sched_set_sched(struct sctp_association *asoc,
+			 enum sctp_sched_type sched);
+int sctp_sched_get_sched(struct sctp_association *asoc);
+int sctp_sched_set_value(struct sctp_association *asoc, __u16 sid,
+			 __u16 value, gfp_t gfp);
+int sctp_sched_get_value(struct sctp_association *asoc, __u16 sid,
+			 __u16 *value);
+void sctp_sched_dequeue_done(struct sctp_outq *q, struct sctp_chunk *ch);
+
+void sctp_sched_dequeue_common(struct sctp_outq *q, struct sctp_chunk *ch);
+int sctp_sched_init_sid(struct sctp_stream *stream, __u16 sid, gfp_t gfp);
+struct sctp_sched_ops *sctp_sched_ops_from_stream(struct sctp_stream *stream);
+
+#endif /* __sctp_stream_sched_h__ */

include/net/sctp/structs.h

@@ -84,7 +84,6 @@ struct sctp_ulpq;
 struct sctp_ep_common;
 struct crypto_shash;
 struct sctp_stream;
-struct sctp_stream_out;
 
 
 #include <net/sctp/tsnmap.h>
@@ -531,8 +530,12 @@ struct sctp_chunk {
 	/* How many times this chunk have been sent, for prsctp RTX policy */
 	int sent_count;
 
+	union {
 		/* This is our link to the per-transport transmitted list.  */
 		struct list_head transmitted_list;
+		/* List in specific stream outq */
+		struct list_head stream_list;
+	};
 
 	/* This field is used by chunks that hold fragmented data.
 	 * For the first fragment this is the list that holds the rest of
@@ -1019,6 +1022,9 @@ struct sctp_outq {
 	/* Data pending that has never been transmitted.  */
 	struct list_head out_chunk_list;
 
+	/* Stream scheduler being used */
+	struct sctp_sched_ops *sched;
+
 	unsigned int out_qlen;	/* Total length of queued data chunks. */
 
 	/* Error of send failed, may used in SCTP_SEND_FAILED event. */
@@ -1325,6 +1331,7 @@ struct sctp_inithdr_host {
 struct sctp_stream_out_ext {
 	__u64 abandoned_unsent[SCTP_PR_INDEX(MAX) + 1];
 	__u64 abandoned_sent[SCTP_PR_INDEX(MAX) + 1];
+	struct list_head outq; /* chunks enqueued by this stream */
 };
 
 struct sctp_stream_out {
@@ -1342,6 +1349,8 @@ struct sctp_stream {
 	struct sctp_stream_in *in;
 	__u16 outcnt;
 	__u16 incnt;
+	/* Current stream being sent, if any */
+	struct sctp_stream_out *out_curr;
 };
 
 #define SCTP_STREAM_CLOSED		0x00

include/uapi/linux/sctp.h

@@ -1088,4 +1088,10 @@ struct sctp_add_streams {
 	uint16_t sas_outstrms;
 };
 
+/* SCTP Stream schedulers */
+enum sctp_sched_type {
+	SCTP_SS_FCFS,
+	SCTP_SS_MAX = SCTP_SS_FCFS
+};
+
 #endif /* _UAPI_SCTP_H */

net/sctp/Makefile

@@ -12,7 +12,7 @@ sctp-y := sm_statetable.o sm_statefuns.o sm_sideeffect.o \
 	  inqueue.o outqueue.o ulpqueue.o \
 	  tsnmap.o bind_addr.o socket.o primitive.o \
 	  output.o input.o debug.o stream.o auth.o \
-	  offload.o
+	  offload.o stream_sched.o
 
 sctp_probe-y := probe.o
 

net/sctp/outqueue.c

@@ -50,6 +50,7 @@
 
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
 
 /* Declare internal functions here.  */
 static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn);
@@ -74,30 +75,36 @@ static void sctp_outq_flush(struct sctp_outq *q, int rtx_timeout, gfp_t gfp);
 static inline void sctp_outq_head_data(struct sctp_outq *q,
 				       struct sctp_chunk *ch)
 {
+	struct sctp_stream_out_ext *oute;
+	__u16 stream;
+
 	list_add(&ch->list, &q->out_chunk_list);
 	q->out_qlen += ch->skb->len;
+
+	stream = sctp_chunk_stream_no(ch);
+	oute = q->asoc->stream.out[stream].ext;
+	list_add(&ch->stream_list, &oute->outq);
 }
 
 /* Take data from the front of the queue. */
 static inline struct sctp_chunk *sctp_outq_dequeue_data(struct sctp_outq *q)
 {
-	struct sctp_chunk *ch = NULL;
-
-	if (!list_empty(&q->out_chunk_list)) {
-		struct list_head *entry = q->out_chunk_list.next;
-
-		ch = list_entry(entry, struct sctp_chunk, list);
-		list_del_init(entry);
-		q->out_qlen -= ch->skb->len;
-	}
-	return ch;
+	return q->sched->dequeue(q);
 }
+
 /* Add data chunk to the end of the queue. */
 static inline void sctp_outq_tail_data(struct sctp_outq *q,
 				       struct sctp_chunk *ch)
 {
+	struct sctp_stream_out_ext *oute;
+	__u16 stream;
+
 	list_add_tail(&ch->list, &q->out_chunk_list);
 	q->out_qlen += ch->skb->len;
+
+	stream = sctp_chunk_stream_no(ch);
+	oute = q->asoc->stream.out[stream].ext;
+	list_add_tail(&ch->stream_list, &oute->outq);
 }
 
 /*
@@ -207,6 +214,7 @@ void sctp_outq_init(struct sctp_association *asoc, struct sctp_outq *q)
 	INIT_LIST_HEAD(&q->retransmit);
 	INIT_LIST_HEAD(&q->sacked);
 	INIT_LIST_HEAD(&q->abandoned);
+	sctp_sched_set_sched(asoc, SCTP_SS_FCFS);
 }
 
 /* Free the outqueue structure and any related pending chunks.
@@ -258,6 +266,7 @@ static void __sctp_outq_teardown(struct sctp_outq *q)
 
 	/* Throw away any leftover data chunks. */
 	while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
+		sctp_sched_dequeue_done(q, chunk);
 
 		/* Mark as send failure. */
 		sctp_chunk_fail(chunk, q->error);
@@ -391,13 +400,14 @@ static int sctp_prsctp_prune_unsent(struct sctp_association *asoc,
 	struct sctp_outq *q = &asoc->outqueue;
 	struct sctp_chunk *chk, *temp;
 
+	q->sched->unsched_all(&asoc->stream);
+
 	list_for_each_entry_safe(chk, temp, &q->out_chunk_list, list) {
 		if (!SCTP_PR_PRIO_ENABLED(chk->sinfo.sinfo_flags) ||
 		    chk->sinfo.sinfo_timetolive <= sinfo->sinfo_timetolive)
 			continue;
 
-		list_del_init(&chk->list);
-		q->out_qlen -= chk->skb->len;
+		sctp_sched_dequeue_common(q, chk);
 		asoc->sent_cnt_removable--;
 		asoc->abandoned_unsent[SCTP_PR_INDEX(PRIO)]++;
 		if (chk->sinfo.sinfo_stream < asoc->stream.outcnt) {
@@ -415,6 +425,8 @@ static int sctp_prsctp_prune_unsent(struct sctp_association *asoc,
 			break;
 	}
 
+	q->sched->sched_all(&asoc->stream);
+
 	return msg_len;
 }
 
@@ -1033,22 +1045,9 @@ static void sctp_outq_flush(struct sctp_outq *q, int rtx_timeout, gfp_t gfp)
 		while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
 			__u32 sid = ntohs(chunk->subh.data_hdr->stream);
 
-			/* RFC 2960 6.5 Every DATA chunk MUST carry a valid
-			 * stream identifier.
-			 */
-			if (chunk->sinfo.sinfo_stream >= asoc->stream.outcnt) {
-
-				/* Mark as failed send. */
-				sctp_chunk_fail(chunk, SCTP_ERROR_INV_STRM);
-				if (asoc->peer.prsctp_capable &&
-				    SCTP_PR_PRIO_ENABLED(chunk->sinfo.sinfo_flags))
-					asoc->sent_cnt_removable--;
-				sctp_chunk_free(chunk);
-				continue;
-			}
-
 			/* Has this chunk expired? */
 			if (sctp_chunk_abandoned(chunk)) {
+				sctp_sched_dequeue_done(q, chunk);
 				sctp_chunk_fail(chunk, 0);
 				sctp_chunk_free(chunk);
 				continue;
@@ -1070,6 +1069,7 @@ static void sctp_outq_flush(struct sctp_outq *q, int rtx_timeout, gfp_t gfp)
 				new_transport = asoc->peer.active_path;
 			if (new_transport->state == SCTP_UNCONFIRMED) {
 				WARN_ONCE(1, "Attempt to send packet on unconfirmed path.");
+				sctp_sched_dequeue_done(q, chunk);
 				sctp_chunk_fail(chunk, 0);
 				sctp_chunk_free(chunk);
 				continue;
@@ -1133,6 +1133,11 @@ static void sctp_outq_flush(struct sctp_outq *q, int rtx_timeout, gfp_t gfp)
 				else
 					asoc->stats.oodchunks++;
 
+				/* Only now it's safe to consider this
+				 * chunk as sent, sched-wise.
+				 */
+				sctp_sched_dequeue_done(q, chunk);
+
 				break;
 
 			default:

net/sctp/sm_sideeffect.c

@@ -50,6 +50,7 @@
 #include <net/sock.h>
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
 
 static int sctp_cmd_interpreter(enum sctp_event event_type,
 				union sctp_subtype subtype,
@@ -1089,6 +1090,8 @@ static void sctp_cmd_send_msg(struct sctp_association *asoc,
 
 	list_for_each_entry(chunk, &msg->chunks, frag_list)
 		sctp_outq_tail(&asoc->outqueue, chunk, gfp);
+
+	asoc->outqueue.sched->enqueue(&asoc->outqueue, msg);
 }
 
 

net/sctp/stream.c

@@ -32,8 +32,61 @@
  *    Xin Long <lucien.xin@gmail.com>
  */
 
+#include <linux/list.h>
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
+
+/* Migrates chunks from stream queues to new stream queues if needed,
+ * but not across associations. Also, removes those chunks to streams
+ * higher than the new max.
+ */
+static void sctp_stream_outq_migrate(struct sctp_stream *stream,
+				     struct sctp_stream *new, __u16 outcnt)
+{
+	struct sctp_association *asoc;
+	struct sctp_chunk *ch, *temp;
+	struct sctp_outq *outq;
+	int i;
+
+	asoc = container_of(stream, struct sctp_association, stream);
+	outq = &asoc->outqueue;
+
+	list_for_each_entry_safe(ch, temp, &outq->out_chunk_list, list) {
+		__u16 sid = sctp_chunk_stream_no(ch);
+
+		if (sid < outcnt)
+			continue;
+
+		sctp_sched_dequeue_common(outq, ch);
+		/* No need to call dequeue_done here because
+		 * the chunks are not scheduled by now.
+		 */
+
+		/* Mark as failed send. */
+		sctp_chunk_fail(ch, SCTP_ERROR_INV_STRM);
+		if (asoc->peer.prsctp_capable &&
+		    SCTP_PR_PRIO_ENABLED(ch->sinfo.sinfo_flags))
+			asoc->sent_cnt_removable--;
+
+		sctp_chunk_free(ch);
+	}
+
+	if (new) {
+		/* Here we actually move the old ext stuff into the new
+		 * buffer, because we want to keep it. Then
+		 * sctp_stream_update will swap ->out pointers.
+		 */
+		for (i = 0; i < outcnt; i++) {
+			kfree(new->out[i].ext);
+			new->out[i].ext = stream->out[i].ext;
+			stream->out[i].ext = NULL;
+		}
+	}
+
+	for (i = outcnt; i < stream->outcnt; i++)
+		kfree(stream->out[i].ext);
+}
 
 static int sctp_stream_alloc_out(struct sctp_stream *stream, __u16 outcnt,
 				 gfp_t gfp)
@@ -87,7 +140,8 @@ static int sctp_stream_alloc_in(struct sctp_stream *stream, __u16 incnt,
 int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
 		     gfp_t gfp)
 {
-	int i;
+	struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream);
+	int i, ret = 0;
 
 	gfp |= __GFP_NOWARN;
 
@@ -97,6 +151,11 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
 	if (outcnt == stream->outcnt)
 		goto in;
 
+	/* Filter out chunks queued on streams that won't exist anymore */
+	sched->unsched_all(stream);
+	sctp_stream_outq_migrate(stream, NULL, outcnt);
+	sched->sched_all(stream);
+
 	i = sctp_stream_alloc_out(stream, outcnt, gfp);
 	if (i)
 		return i;
@@ -105,20 +164,27 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
 	for (i = 0; i < stream->outcnt; i++)
 		stream->out[i].state = SCTP_STREAM_OPEN;
 
+	sched->init(stream);
+
 in:
 	if (!incnt)
-		return 0;
+		goto out;
 
 	i = sctp_stream_alloc_in(stream, incnt, gfp);
 	if (i) {
-		kfree(stream->out);
-		stream->out = NULL;
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto free;
 	}
 
 	stream->incnt = incnt;
+	goto out;
 
-	return 0;
+free:
+	sched->free(stream);
+	kfree(stream->out);
+	stream->out = NULL;
+out:
+	return ret;
 }
 
 int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)
@@ -130,13 +196,15 @@ int sctp_stream_init_ext(struct sctp_stream *stream, __u16 sid)
 		return -ENOMEM;
 	stream->out[sid].ext = soute;
 
-	return 0;
+	return sctp_sched_init_sid(stream, sid, GFP_KERNEL);
 }
 
 void sctp_stream_free(struct sctp_stream *stream)
 {
+	struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream);
 	int i;
 
+	sched->free(stream);
 	for (i = 0; i < stream->outcnt; i++)
 		kfree(stream->out[i].ext);
 	kfree(stream->out);
@@ -156,6 +224,10 @@ void sctp_stream_clear(struct sctp_stream *stream)
 
 void sctp_stream_update(struct sctp_stream *stream, struct sctp_stream *new)
 {
+	struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream);
+
+	sched->unsched_all(stream);
+	sctp_stream_outq_migrate(stream, new, new->outcnt);
 	sctp_stream_free(stream);
 
 	stream->out = new->out;
@@ -163,6 +235,8 @@ void sctp_stream_update(struct sctp_stream *stream, struct sctp_stream *new)
 	stream->outcnt = new->outcnt;
 	stream->incnt  = new->incnt;
 
+	sched->sched_all(stream);
+
 	new->out = NULL;
 	new->in  = NULL;
 }

net/sctp/stream_sched.c

+/* SCTP kernel implementation
+ * (C) Copyright Red Hat Inc. 2017
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * These functions manipulate sctp stream queue/scheduling.
+ *
+ * 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 addresched(es):
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *    Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
+ */
+
+#include <linux/list.h>
+#include <net/sctp/sctp.h>
+#include <net/sctp/sm.h>
+#include <net/sctp/stream_sched.h>
+
+/* First Come First Serve (a.k.a. FIFO)
+ * RFC DRAFT ndata Section 3.1
+ */
+static int sctp_sched_fcfs_set(struct sctp_stream *stream, __u16 sid,
+			       __u16 value, gfp_t gfp)
+{
+	return 0;
+}
+
+static int sctp_sched_fcfs_get(struct sctp_stream *stream, __u16 sid,
+			       __u16 *value)
+{
+	*value = 0;
+	return 0;
+}
+
+static int sctp_sched_fcfs_init(struct sctp_stream *stream)
+{
+	return 0;
+}
+
+static int sctp_sched_fcfs_init_sid(struct sctp_stream *stream, __u16 sid,
+				    gfp_t gfp)
+{
+	return 0;
+}
+
+static void sctp_sched_fcfs_free(struct sctp_stream *stream)
+{
+}
+
+static void sctp_sched_fcfs_enqueue(struct sctp_outq *q,
+				    struct sctp_datamsg *msg)
+{
+}
+
+static struct sctp_chunk *sctp_sched_fcfs_dequeue(struct sctp_outq *q)
+{
+	struct sctp_stream *stream = &q->asoc->stream;
+	struct sctp_chunk *ch = NULL;
+	struct list_head *entry;
+
+	if (list_empty(&q->out_chunk_list))
+		goto out;
+
+	if (stream->out_curr) {
+		ch = list_entry(stream->out_curr->ext->outq.next,
+				struct sctp_chunk, stream_list);
+	} else {
+		entry = q->out_chunk_list.next;
+		ch = list_entry(entry, struct sctp_chunk, list);
+	}
+
+	sctp_sched_dequeue_common(q, ch);
+
+out:
+	return ch;
+}
+
+static void sctp_sched_fcfs_dequeue_done(struct sctp_outq *q,
+					 struct sctp_chunk *chunk)
+{
+}
+
+static void sctp_sched_fcfs_sched_all(struct sctp_stream *stream)
+{
+}
+
+static void sctp_sched_fcfs_unsched_all(struct sctp_stream *stream)
+{
+}
+
+static struct sctp_sched_ops sctp_sched_fcfs = {
+	.set = sctp_sched_fcfs_set,
+	.get = sctp_sched_fcfs_get,
+	.init = sctp_sched_fcfs_init,
+	.init_sid = sctp_sched_fcfs_init_sid,
+	.free = sctp_sched_fcfs_free,
+	.enqueue = sctp_sched_fcfs_enqueue,
+	.dequeue = sctp_sched_fcfs_dequeue,
+	.dequeue_done = sctp_sched_fcfs_dequeue_done,
+	.sched_all = sctp_sched_fcfs_sched_all,
+	.unsched_all = sctp_sched_fcfs_unsched_all,
+};
+
+/* API to other parts of the stack */
+
+struct sctp_sched_ops *sctp_sched_ops[] = {
+	&sctp_sched_fcfs,
+};
+
+int sctp_sched_set_sched(struct sctp_association *asoc,
+			 enum sctp_sched_type sched)
+{
+	struct sctp_sched_ops *n = sctp_sched_ops[sched];
+	struct sctp_sched_ops *old = asoc->outqueue.sched;
+	struct sctp_datamsg *msg = NULL;
+	struct sctp_chunk *ch;
+	int i, ret = 0;
+
+	if (old == n)
+		return ret;
+
+	if (sched > SCTP_SS_MAX)
+		return -EINVAL;
+
+	if (old) {
+		old->free(&asoc->stream);
+
+		/* Give the next scheduler a clean slate. */
+		for (i = 0; i < asoc->stream.outcnt; i++) {
+			void *p = asoc->stream.out[i].ext;
+
+			if (!p)
+				continue;
+
+			p += offsetofend(struct sctp_stream_out_ext, outq);
+			memset(p, 0, sizeof(struct sctp_stream_out_ext) -
+				     offsetofend(struct sctp_stream_out_ext, outq));
+		}
+	}
+
+	asoc->outqueue.sched = n;
+	n->init(&asoc->stream);
+	for (i = 0; i < asoc->stream.outcnt; i++) {
+		if (!asoc->stream.out[i].ext)
+			continue;
+
+		ret = n->init_sid(&asoc->stream, i, GFP_KERNEL);
+		if (ret)
+			goto err;
+	}
+
+	/* We have to requeue all chunks already queued. */
+	list_for_each_entry(ch, &asoc->outqueue.out_chunk_list, list) {
+		if (ch->msg == msg)
+			continue;
+		msg = ch->msg;
+		n->enqueue(&asoc->outqueue, msg);
+	}
+
+	return ret;
+
+err:
+	n->free(&asoc->stream);
+	asoc->outqueue.sched = &sctp_sched_fcfs; /* Always safe */
+
+	return ret;
+}
+
+int sctp_sched_get_sched(struct sctp_association *asoc)
+{
+	int i;
+
+	for (i = 0; i <= SCTP_SS_MAX; i++)
+		if (asoc->outqueue.sched == sctp_sched_ops[i])
+			return i;
+
+	return 0;
+}
+
+int sctp_sched_set_value(struct sctp_association *asoc, __u16 sid,
+			 __u16 value, gfp_t gfp)
+{
+	if (sid >= asoc->stream.outcnt)
+		return -EINVAL;
+
+	if (!asoc->stream.out[sid].ext) {
+		int ret;
+
+		ret = sctp_stream_init_ext(&asoc->stream, sid);
+		if (ret)
+			return ret;
+	}
+
+	return asoc->outqueue.sched->set(&asoc->stream, sid, value, gfp);
+}
+
+int sctp_sched_get_value(struct sctp_association *asoc, __u16 sid,
+			 __u16 *value)
+{
+	if (sid >= asoc->stream.outcnt)
+		return -EINVAL;
+
+	if (!asoc->stream.out[sid].ext)
+		return 0;
+
+	return asoc->outqueue.sched->get(&asoc->stream, sid, value);
+}
+
+void sctp_sched_dequeue_done(struct sctp_outq *q, struct sctp_chunk *ch)
+{
+	if (!list_is_last(&ch->frag_list, &ch->msg->chunks)) {
+		struct sctp_stream_out *sout;
+		__u16 sid;
+
+		/* datamsg is not finish, so save it as current one,
+		 * in case application switch scheduler or a higher
+		 * priority stream comes in.
+		 */
+		sid = sctp_chunk_stream_no(ch);
+		sout = &q->asoc->stream.out[sid];
+		q->asoc->stream.out_curr = sout;
+		return;
+	}
+
+	q->asoc->stream.out_curr = NULL;
+	q->sched->dequeue_done(q, ch);
+}
+
+/* Auxiliary functions for the schedulers */
+void sctp_sched_dequeue_common(struct sctp_outq *q, struct sctp_chunk *ch)
+{
+	list_del_init(&ch->list);
+	list_del_init(&ch->stream_list);
+	q->out_qlen -= ch->skb->len;
+}
+
+int sctp_sched_init_sid(struct sctp_stream *stream, __u16 sid, gfp_t gfp)
+{
+	struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream);
+
+	INIT_LIST_HEAD(&stream->out[sid].ext->outq);
+	return sched->init_sid(stream, sid, gfp);
+}
+
+struct sctp_sched_ops *sctp_sched_ops_from_stream(struct sctp_stream *stream)
+{
+	struct sctp_association *asoc;
+
+	asoc = container_of(stream, struct sctp_association, stream);
+
+	return asoc->outqueue.sched;
+}