sctp: add weighted fair queueing stream scheduler

As it says in rfc8260#section-3.6 about the weighted fair queueing
scheduler:

A Weighted Fair Queueing scheduler between the streams is used. The
weight is configurable per outgoing SCTP stream. This scheduler
considers the lengths of the messages of each stream and schedules
them in a specific way to use the capacity according to the given
weights. If the weight of stream S1 is n times the weight of stream
S2, the scheduler should assign to stream S1 n times the capacity it
assigns to stream S2. The details are implementation dependent.
Interleaving user messages allows for a better realization of the
capacity usage according to the given weights.

This patch adds Weighted Fair Queueing Scheduler actually based on
the code of Fair Capacity Scheduler by adding fc_weight into struct
sctp_stream_out_ext and taking it into account when sorting stream->
fc_list in sctp_sched_fc_sched() and sctp_sched_fc_dequeue_done().

Signed-off-by: Xin Long <[e-mail]>
Acked-by: Marcelo Ricardo Leitner <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

include/net/sctp/stream_sched.h

···
 void sctp_sched_ops_prio_init(void);
 void sctp_sched_ops_rr_init(void);
 void sctp_sched_ops_fc_init(void);
+void sctp_sched_ops_wfq_init(void);
 
 #endif /* __sctp_stream_sched_h__ */

include/net/sctp/structs.h

···
 		struct {
 			struct list_head fc_list;
 			__u32 fc_length;
+			__u16 fc_weight;
 		};
 	};
 };

include/uapi/linux/sctp.h

···
 	SCTP_SS_PRIO,
 	SCTP_SS_RR,
 	SCTP_SS_FC,
-	SCTP_SS_MAX = SCTP_SS_FC
+	SCTP_SS_WFQ,
+	SCTP_SS_MAX = SCTP_SS_WFQ
 };
 
 /* Probe Interval socket option */

net/sctp/stream_sched.c

···
 	sctp_sched_ops_prio_init();
 	sctp_sched_ops_rr_init();
 	sctp_sched_ops_fc_init();
+	sctp_sched_ops_wfq_init();
 }
 
 static void sctp_sched_free_sched(struct sctp_stream *stream)

net/sctp/stream_sched_fc.c

···
 #include <net/sctp/sm.h>
 #include <net/sctp/stream_sched.h>
 
-/* Fair Capacity handling
- * RFC 8260 section 3.5
+/* Fair Capacity and Weighted Fair Queueing handling
+ * RFC 8260 section 3.5 and 3.6
  */
 static void sctp_sched_fc_unsched_all(struct sctp_stream *stream);
+
+static int sctp_sched_wfq_set(struct sctp_stream *stream, __u16 sid,
+			      __u16 weight, gfp_t gfp)
+{
+	struct sctp_stream_out_ext *soute = SCTP_SO(stream, sid)->ext;
+
+	if (!weight)
+		return -EINVAL;
+
+	soute->fc_weight = weight;
+	return 0;
+}
+
+static int sctp_sched_wfq_get(struct sctp_stream *stream, __u16 sid,
+			      __u16 *value)
+{
+	struct sctp_stream_out_ext *soute = SCTP_SO(stream, sid)->ext;
+
+	*value = soute->fc_weight;
+	return 0;
+}
 
 static int sctp_sched_fc_set(struct sctp_stream *stream, __u16 sid,
 			     __u16 weight, gfp_t gfp)
···
 
 	INIT_LIST_HEAD(&soute->fc_list);
 	soute->fc_length = 0;
+	soute->fc_weight = 1;
 
 	return 0;
 }
···
 		return;
 
 	list_for_each_entry(pos, &stream->fc_list, fc_list)
-		if (pos->fc_length >= soute->fc_length)
+		if ((__u64)pos->fc_length * soute->fc_weight >=
+		    (__u64)soute->fc_length * pos->fc_weight)
 			break;
 	list_add_tail(&soute->fc_list, &pos->fc_list);
 }
···
 
 	pos = soute;
 	list_for_each_entry_continue(pos, &stream->fc_list, fc_list)
-		if (pos->fc_length >= soute->fc_length)
+		if ((__u64)pos->fc_length * soute->fc_weight >=
+		    (__u64)soute->fc_length * pos->fc_weight)
 			break;
 	list_move_tail(&soute->fc_list, &pos->fc_list);
 }
···
 void sctp_sched_ops_fc_init(void)
 {
 	sctp_sched_ops_register(SCTP_SS_FC, &sctp_sched_fc);
+}
+
+static struct sctp_sched_ops sctp_sched_wfq = {
+	.set = sctp_sched_wfq_set,
+	.get = sctp_sched_wfq_get,
+	.init = sctp_sched_fc_init,
+	.init_sid = sctp_sched_fc_init_sid,
+	.free_sid = sctp_sched_fc_free_sid,
+	.enqueue = sctp_sched_fc_enqueue,
+	.dequeue = sctp_sched_fc_dequeue,
+	.dequeue_done = sctp_sched_fc_dequeue_done,
+	.sched_all = sctp_sched_fc_sched_all,
+	.unsched_all = sctp_sched_fc_unsched_all,
+};
+
+void sctp_sched_ops_wfq_init(void)
+{
+	sctp_sched_ops_register(SCTP_SS_WFQ, &sctp_sched_wfq);
 }