These patches focus on the Initiator and partially on Listener side.
The next options in userspace are available:
a) sendto(..., ..., ..., MSG_FASTOPEN, ..., ...);
b) setsockopt(..., SOL_TCP, TCP_FASTOPEN, ..., ...);

These patches implement Appendix-B of RFC8684 (MPTFO).

We would like to credit Paulo Abeni, Mat Martineau, Matthieu Baerts and
Benjamin Hesmans for advices and ideas that improved these patches.

Dmytro Shytyi (7):
  mptcp: add __mptcp_pre_connect() helper
  mptcp: add __mptcp_stream_connect() helper
  mptcp: introduce MSG_FASTOPEN flag.
  mptcp: implement delayed seq generation for passive fastopen
  mptcp: add subflow_v(4,6)_send_synack()
  mptcp: add TCP_FASTOPEN sock option
  selftests: mptfo initiator/listener

 net/mptcp/Makefile                            |   2 +-
 net/mptcp/fastopen.c                          |  96 +++++++++++++++++
 net/mptcp/options.c                           |   5 +
 net/mptcp/protocol.c                          |  64 +++++++----
 net/mptcp/protocol.h                          |  13 +++
 net/mptcp/sockopt.c                           |   5 +-
 net/mptcp/subflow.c                           |  42 ++++++++
 tools/testing/selftests/net/mptcp/mptfo.sh    |  13 +++
 .../selftests/net/mptcp/mptfo_initiator.c     |  43 ++++++++
 .../selftests/net/mptcp/mptfo_listener.c      | 100 ++++++++++++++++++
 10 files changed, 360 insertions(+), 23 deletions(-)
 create mode 100644 net/mptcp/fastopen.c
 create mode 100644 tools/testing/selftests/net/mptcp/mptfo.sh
 create mode 100644 tools/testing/selftests/net/mptcp/mptfo_initiator.c
 create mode 100644 tools/testing/selftests/net/mptcp/mptfo_listener.c

-- 
2.34.1