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 v3:
- patch 1: split exceptions + set msk port to 0 like before this series
- patches 2-3: new: from patch 1 + fix
- patch 6: use new is_init_id0 helper
- patch 8: avoid conflicts with WIP BPF MPTCP PM patches
- Link to v2: https://patch.msgid.link/20260806-mptcp-pm-userspace-id0-case-v2-0-fea1808e1c57@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) (8):
      mptcp: pm: userspace: properly handle the ID0 case
      mptcp: pm: userspace: lookup: match port in priority
      mptcp: pm: userspace: ID0 is not part of local_addr_used
      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                        | 93 +++++++++++++------------
 net/mptcp/protocol.h                            |  1 +
 tools/testing/selftests/net/mptcp/mptcp_join.sh |  7 +-
 4 files changed, 59 insertions(+), 50 deletions(-)
---
base-commit: 5cb376373d7f0915c9c2dc6648631bb54ab7a6cb
change-id: 20260724-mptcp-pm-userspace-id0-case-f074f64466c8

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

Hello,

On 07/08/2026 10:41, Matthieu Baerts (NGI0) wrote:
> 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.

FYI, it looks like all comments from Sashiko are addressing issues fixed
in the following patches, or by other series. Then, I think everything
is OK on Sashiko's side.

(I'm not sure how to tell Sashiko to look at the next patches before
complaining: the split is needed, because different issues are addressed
in this series, and introduced by different commits.)

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

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/31163906637

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/91f23e3aba21
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1142037


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)