In MPTCP, the local address and port used by the initial subflow has the
ID "0". It means that when this address and port are used for some
operations -- e.g. creating a new subflow -- they should be linked to
the ID0, and no other addresses and ports can get this special ID while
the initial IP address and port is used.

Instead of dealing with the ID0 case as an exception, add it to the
local addr list, and deal with it like the others, with minor
exceptions. That way, it seems easier to maintain instead of adding new
exceptions at a few places, at the cost of a few more bytes, which seems
OK in this mode.

The first patch modifies add the initial address to the list, and the
others remove exceptions, and validate that in the selftests.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- patch 1: commit msg + local_addr_used and needs_id exceptions
- patch 2: commit msg
- Link to v1: https://patch.msgid.link/20260727-mptcp-pm-userspace-id0-case-v1-0-9877f02a9bae@kernel.org

---
Matthieu Baerts (NGI0) (6):
      mptcp: pm: userspace: properly handle the ID0 case
      mptcp: pm: userspace: allow announcing ID0 addr
      mptcp: pm: userspace: no ID0 exception for RM_ADDR
      mptcp: pm: userspace: don't dump initial ID0
      selftests: mptcp: join: new ID0 subflow from the right IP
      mptcp: pm: restrict in-kernel worker actions to this PM

 net/mptcp/pm.c                                  |  8 ++-
 net/mptcp/pm_userspace.c                        | 91 ++++++++++++-------------
 net/mptcp/protocol.h                            |  1 +
 tools/testing/selftests/net/mptcp/mptcp_join.sh |  7 +-
 4 files changed, 55 insertions(+), 52 deletions(-)
---
base-commit: 0715f5ba093a581def25b88da61c987b1719bc6d
change-id: 20260724-mptcp-pm-userspace-id0-case-f074f64466c8

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 (except selftest_mptcp_join): Success! ✅
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Success! ✅
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/31087551998

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/63d11d6186ef
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1141314


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)