RE: [PATCH RFC] sctp: Update HEARTBEAT timer immediately after user changed HB.interval

quoted

+
+				/* Update the heartbeat timer immediately. */
+				if (!mod_timer(&trans->hb_timer,
+					    sctp_transport_timeout(trans)))
+					sctp_transport_hold(trans);

This is causes a rather inconsistent behavior in that it doesn't
account of the amount of time left on the hb timer.  Thus it doesn't
always do what commit log implies.  If the remaining time is shorter
then the new timeout value, it will take longer till the next HB
the application expects.

Being able to stop heartbeats being sent by repeatedly configuring
the interval is certainly not a good idea!

If the application has very strict timing requirement on the HBs, it
should trigger the HB manually.

We could rework the code to allow the combination of
SPP_HB_DEMAND | SPP_HB_ENABLE to work as follows:
  1) update the timer to the new value
  2) Send an immediate HB
     a) Update the hb timeout.

2a should probably be done regardless since it can cause 2 HB to be
outstanding at the same time.

Sending a heartbeat 'on demand' might be problematic if one
has also just been sent (from the timer).

I'd have thought that you wouldn't want to send a heartbeat while
still expecting a response from the previous one (this might require
splitting the time interval in two).

	David