On Tue, Sep 29, 2020 at 09:49:03PM +0800, Xin Long wrote:

sctp_mtu_payload() is for calculating the frag size before making
chunks from a msg. So we should only add udphdr size to overhead
when udp socks are listening, as only then sctp can handling the

                                               "handle"   ^^^^

incoming sctp over udp packets and outgoing sctp over udp packets
will be possible.

Note that we can't do this according to transport->encap_port, as
different transports may be set to different values, while the
chunks were made before choosing the transport, we could not be
able to meet all rfc6951#section-5.6 requires.

I don't follow this last part. I guess you're referring to the fact
that it won't grow back the PMTU if it is not encapsulating anymore.
If that's it, then changelog should be different here.  As is, it
seems it is not abiding by the RFC, but it is, as that's a 'SHOULD'.

Maybe s/requires\.$/recommends./ ?