[PATCH net 0/7] mptcp: fix inconsistent backup usage

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

In all the MPTCP backup related tests, the backup flag was set on one
side, and the expected behaviour is to have both sides respecting this
decision. That's also the "natural" way, and what the users seem to
expect.

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

Patch 1 modifies the packet scheduler to check if the backup flag has
been set on both directions, not to change its behaviour after having
applied the following patches. That's what the default packet scheduler
should have done since the beginning in v5.7.

Patch 2 fixes the backup flag being mirrored on the MPJ+SYN+ACK by
accident since its introduction in v5.7. Instead, the received and sent
backup flags are properly distinguished in requests.

Patch 3 stops setting the received backup flag as well when sending an
MP_PRIO, something that was done since the MP_PRIO support in v5.12.

Patch 4 adds related and missing MIB counters to be able to easily check
if MP_JOIN are sent with a backup flag. Certainly because these counters
were not there, the behaviour that is fixed by patches here was not
properly verified.

Patch 5 validates the previous patch by extending the MPTCP Join
selftest.

Patch 6 fixes the backup support in signal endpoints: if a signal
endpoint had the backup flag, it was not set in the MPJ+SYN+ACK as
expected. It was only set for ongoing connections, but not future ones
as expected, since the introduction of the backup flag in endpoints in
v5.10.

Patch 7 validates the previous patch by extending the MPTCP Join
selftest as well.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Matthieu Baerts (NGI0) (7):
      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

 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                                  | 12 +++++
 net/mptcp/pm_netlink.c                          | 19 ++++++-
 net/mptcp/pm_userspace.c                        | 18 +++++++
 net/mptcp/protocol.c                            | 10 ++--
 net/mptcp/protocol.h                            |  4 ++
 net/mptcp/subflow.c                             | 10 ++++
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 72 ++++++++++++++++++++-----
 11 files changed, 132 insertions(+), 21 deletions(-)
---
base-commit: 301927d2d2eb8e541357ba850bc7a1a74dbbd670
change-id: 20240727-upstream-net-20240727-mptcp-backup-signal-948235f2ad08

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