Kernel SCTP and DCCP?

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

What applications either do, or reasonably could, use SCTP and DCCP in
the NetBSD kernel?  How do we test them?

These are very large code bases that have been off by default for a
long time, and appear to have had essentially no maintenance (other
than build fixes and typo fixes) since 2019.  But I don't know what
they would be useful for, or even how to use them.

- I know SCTP is used by webrtc, but as far as I know all webrtc
  implementations just use userland SCTP encapsulated in (DTLS over)
  UDP, so the kernel SCTP implementation is not relevant.

- I know (in principle) SCTP is used in the control planes of mobile
  telecoms but I don't know how I would even interact with or simulate
  such a network if I don't work at a mobile telecom company.

- We appear to have zero userland programs, or automatic tests, that
  mention SCTP and DCCP at all, except for kdump(1) and netstat(1)
  output formatters.

- We appear to have no documentation on the wiki or in the guide about
  how to do anything with SCTP or DCCP.  If I had to fix a
  vulnerability in it, I wouldn't even know where to start testing it
  to make sure I didn't break something.

Linux seems to have dropped DCCP in version 6.16.  FreeBSD seems not
to have ever had kernel DCCP at all.

Is this large code base worth the maintenance costs?  If it is useful,
can the folks for whom it is useful suggest how to keep it exercised,
and contribute automatic tests for the basic functionality?