[MPTCP][PATCH v6 mptcp-next 0/5] MP_FAIL support

[Geliang Tang <geliangtang@gmail.com>]

From: Geliang Tang <geliangtang@xiaomi.com>

v6: only rebased patch 1
 - move the struct member 'fail_seq' behind 'ext_copy'.
 - define OPTION_MPTCP_FAIL to BIT(12), BIT(11) is used by DSS
 - move the MP_FAIL writing code at the beginning of mptcp_write_options,
   and add the 'unlikely' tag.
 - tag: export/20210728T080904

v5:
 - patch 1, change "ret = true;" to "return true;"
 - patch 3, in the single-subflow case, send MP_FAIL and receive the
   echo, then temporarily handled by reset.

v4:
 - just deal with the multiple subflows case, put the single subflow
   case into the new 'infinite mapping' part.

v3:
 - respond with MP_FAIL
 - add single subflow check
 - add infinite mapping sending and receiving
 - export/20210626T054902

v2:
 - MP_FAIL logic:
   * Peer B send a DSS to peer A, and the data has been modify by the
  middleboxes, then peer A detects the bad checksum.
   * In the multiple subflows case, peer A sends MP_FAIL+RST back to peer B,
  and peer A discards the data following the bad data sequence number. Peer
  B receives this MP_FAIL+RST, and close this subflow.
   * In the single subflow case, using the simple implementation, peer A
  sends MP_FAIL back to peer B, and peer A fallback to a regular TCP. Peer
  B receives this MP_FAIL, and fallback to a regular TCP.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/52

Geliang Tang (5):
  mptcp: MP_FAIL suboption sending
  mptcp: MP_FAIL suboption receiving
  mptcp: send out MP_FAIL when data checksum fails
  mptcp: add the mibs for MP_FAIL
  selftests: mptcp: add MP_FAIL mibs check

 include/net/mptcp.h                           |  5 +-
 net/mptcp/mib.c                               |  2 +
 net/mptcp/mib.h                               |  2 +
 net/mptcp/options.c                           | 78 ++++++++++++++++++-
 net/mptcp/pm.c                                | 20 +++++
 net/mptcp/protocol.h                          | 20 +++++
 net/mptcp/subflow.c                           | 18 +++++
 .../testing/selftests/net/mptcp/mptcp_join.sh | 38 +++++++++
 8 files changed, 178 insertions(+), 5 deletions(-)

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2.31.1