In all the backup tests we have, the backup flag is set on one side, and
the expected behaviour is to have both sides respecting this decision.

On the scheduler side, only the 'backup' field is checked, which is
supposed to be set only if the other peer flagged a subflow as backup.
But in various places, this flag is set when the local host flagged the
subflow as backup.

One last thing that has been fixed is the backup flag in 'signal'
endpoints: it was working only when setting the backup flag while the
connection was already opened. That's what the MPJ selftests were doing
to check that the signal endpoint were supporting the backup flag (on
purpose I guess, because the support was broken in MP_JOIN...).

The last two patches adapt the BPF selftests to mimic what is now done
by the in-kernel packets scheduler.

Note that the Packetdrill tests need to be updated because the behaviour
has been changed / fixed:

  https://github.com/multipath-tcp/packetdrill/pull/152

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- new patches 4 and 5.
- split patch 6 in two (code then tests) to ease the backports.
- patch 6 addresses Mat's comments, and support the ID0 case.
- Link to v1: https://lore.kernel.org/r/20240711-mptcp-backup-mpj-v1-0-d45506182a9e@kernel.org

---
Matthieu Baerts (NGI0) (9):
      mptcp: sched: check both directions for backup
      mptcp: distinguish rcv vs sent backup flag in requests
      mptcp: pm: only set request_bkup flag when sending MP_PRIO
      mptcp: mib: count MPJ with backup flag
      selftests: mptcp: join: validate backup in MPJ
      mptcp: pm: fix backup support in signal endpoints
      selftests: mptcp: join: check backup support in signal endp
      Squash to "selftests/bpf: Add bpf_bkup scheduler & test"
      Squash to "selftests/bpf: Add bpf_burst scheduler & test"

 include/trace/events/mptcp.h                       |  2 +-
 net/mptcp/mib.c                                    |  2 +
 net/mptcp/mib.h                                    |  2 +
 net/mptcp/options.c                                |  2 +-
 net/mptcp/pm.c                                     | 15 +++--
 net/mptcp/pm_netlink.c                             | 24 +++++++-
 net/mptcp/pm_userspace.c                           | 25 +++++++-
 net/mptcp/protocol.c                               | 10 +--
 net/mptcp/protocol.h                               | 12 +++-
 net/mptcp/subflow.c                                | 16 ++++-
 tools/testing/selftests/bpf/progs/mptcp_bpf_bkup.c |  3 +-
 .../testing/selftests/bpf/progs/mptcp_bpf_burst.c  | 12 ++--
 tools/testing/selftests/net/mptcp/mptcp_join.sh    | 72 +++++++++++++++++-----
 13 files changed, 159 insertions(+), 38 deletions(-)
---
base-commit: 06bd6d6c3416101af4881b6f3a0830ccca97c056
change-id: 20240711-mptcp-backup-mpj-2f8369fad366

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

Hi Matthieu,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal: Unstable: 4 failed test(s): packetdrill_mp_join packetdrill_mp_prio packetdrill_regressions packetdrill_syscalls 🔴
- KVM Validation: debug: Unstable: 4 failed test(s): packetdrill_mp_join packetdrill_mp_prio packetdrill_regressions packetdrill_syscalls 🔴
- KVM Validation: btf (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/9964158437

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/12a566ab8700
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=871789


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)