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-13
Tested-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>

1 files changed, 12 insertions, 3 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index c48f7999fe9b..3c22a30fd71b 100644
--- a/include/net/sctp/structs.h
+++ b/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;
 
-        /* This is our link to the per-transport transmitted list.  */
-        struct list_head transmitted_list;
+        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