[RFC mptcp-next 0/6] MP_FAIL echo and retrans

[Geliang Tang <geliang.tang@suse.com>]

This patchset added MP_FAIL echo and retrans support. Except the last
patch, others work well.

Here I have some questions about it.

1. How to distinguish an MP_FAIL packet and an MP_FAIL echo packet?

Unlike ADD_ADDR, there's no echo bit in a MP_FAIL packet. Patch 1 used
simple method to distinguish them.

MP_FAIL carries the data sequence number of the checksum failure.
MP_FAIL echo carries the received data sequence number of a MP_FAIL.

2. For the multiple subflow case, MP_FAIL echo is sent on another subflow,
not the subflow receiving this MP_FAIL. Since the receiving subflow will
be closed by MP_RST after a while.

3. Patch 5 added mp_fail_timer as a struct member of struct
mptcp_subflow_context. Is there a better place to add this timer?

4. Just like the way of dropping the ADD_ADDR packets in the ADD_ADDR
timeout testcases, patch 6 tried to use iptables bpf to drop the MP_FAIL
packets too. But it doesn't work.

Drop ADD_ADDR packets using this bpf rule:

 "nfbpf_compile '(ip && (ip[54] & 0xf0) == 0x30) ||
                 (ip6 && (ip6[74] & 0xf0) == 0x30)'"

I used a similar rule to drop MP_FAIL packets:

 "nfbpf_compile '(ip && (ip[54] & 0xf0) == 0x60) ||
                 (ip6 && (ip6[74] & 0xf0) == 0x60)'"

I thinks the offset shouldn't be 54 or 74 here. Matt, could you please
give me some help about how to get the right offset values?

Thanks.
-Geliang

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/261
Depends on: the "add mp_fail testcases" series.

Geliang Tang (6):
  mptcp: add MP_FAIL echo support
  mptcp: add mibs for MP_FAIL echo
  selftests: mptcp: add MP_FAIL echo mibs check
  mptcp: add a new sysctl mp_fail_timeout
  mptcp: add MP_FAIL retrans support
  selftests: mptcp: MP_FAIL timeout testcases TODO

 Documentation/networking/mptcp-sysctl.rst     | 10 +++
 net/mptcp/ctrl.c                              | 14 ++++
 net/mptcp/mib.c                               |  2 +
 net/mptcp/mib.h                               |  2 +
 net/mptcp/options.c                           | 23 ++++-
 net/mptcp/pm.c                                | 41 ++++++++-
 net/mptcp/protocol.c                          |  1 +
 net/mptcp/protocol.h                          |  7 ++
 net/mptcp/subflow.c                           | 30 ++++++-
 .../testing/selftests/net/mptcp/mptcp_join.sh | 84 +++++++++++++++++++
 10 files changed, 207 insertions(+), 7 deletions(-)

-- 
2.34.1