I'll focus on the eventhandler changes...

I would suggest to get

• the generic fixes from above in head first
• then get the eventhandler stuff or the dtrace changes in as separate commits.

That reduces the patch set and really focusses on the changes related to allowing SCTP to be a module.

What is the benefit of moving it? Also, at the new location, you perform the checks for every tcp_output() call, although it is only needed when dealing with the connect() call.
Furthermore, if you remove it from tcp_connect(), you also need to remove it from tcp6_connect().

Allow at least one byte of payload to ensure that making progress is possible. This was suggested in the transport telco.

I'm contemplating what we gain by this change... We get a much more complex definition of mtod() and, for example, in the case of the SCTP source, which are shared with other BSD like platforms which don't make that change, we have to provide a way to do it still the old way. I guess, I have to replace mtod() by SCTP_MTOD() with the 2 argument semantic in the SCTP sources and then make platform specific definitions: On FreeBSD, call your version and do the explicit cast, on the other platforms just call mtod(). Another point is that these mechanical global changes might make MFCing code harder...

In D21567#469977, @rscheff_gmx.at wrote:

Checked this patch with various "pure FIN after hole" and "data FIN after hole" combinations; the FIN bit becomes part of the SACK (and DSACK) blocks, as it should be when considering that FIN is part of the sequence number space.

The patch has been updated to address Richard's comments.

Address Richard's comments.

In D21567#469962, @rrs wrote:

I would like to see the Rack version of the code be identical to the tcp_input version.. i.e. it should check
if ((tlen > 0) && (tp->t_flags & TF_SACK_PERMITED))
The soon to be committed version of rack will allow a user to use the stack without sack.. so it is best to
put this in place now.

Add a check to the RACK code whether the SACK extension is enabled. This was requested by rrs@.