[PATCH mptcp-next v3 0/3] mptcp: MSG_ERRQUEUE support on the parent socket

[David Carlier <devnexen@gmail.com>]

MPTCP already advertises IP_RECVERR/IPV6_RECVERR as supported, but the
parent socket does not currently provide usable MSG_ERRQUEUE handling.

This series wires the MPTCP socket up to the IPv4/IPv6 error queue
paths. It propagates RECVERR-related sockopts to existing and future
subflows, makes poll() report pending errqueue activity through the
parent socket, and allows recvmsg(MSG_ERRQUEUE) on the MPTCP socket to
consume queued errors with the parent socket ABI.

The series also handles mixed-family subflows by applying the matching
sockopt according to each subflow family, and avoids silently losing an
error skb if requeueing to the parent socket fails under rmem pressure.

v2 -> v3:
  - Only consume ssk->sk_err in the fallback / MPC-connect branch of
    __mptcp_subflow_error_report(). Steady-state MPTCP now leaves
    TCP's one-shot sk_err to TCP's own consumer instead of silently
    draining it via sock_error().
  - In mptcp_recv_error(), also route to inet_recv_error() when
    sk->sk_err is set, so a fallback-propagated error reaches userspace
    even when the parent errqueue is empty.
  - Scope the new selftest to IP_RECVERR sockopt propagation only.
    End-to-end errqueue delivery (TX timestamps, ICMP, zerocopy)
    depends on subflow-side producers that are out of scope for this
    series and will be covered by follow-up work. Fixes the
    mptcp_sockopt selftest timeout reported by the MPTCP CI on v2.

v1 -> v2:
  - Retargeted to mptcp-next per Matthieu Baerts' feedback (net-next
    closed during the merge window; iterate on the MPTCP tree).
  - Guard mptcp_setsockopt_v6_recverr() and its dispatch cases in
    mptcp_setsockopt_v6() with #if IS_ENABLED(CONFIG_IPV6) to fix
    the MPTCP CI link break on without_ipv6/with_mptcp configs
    (undefined reference to ipv6_setsockopt).

v1: https://lore.kernel.org/mptcp/20260421152216.38127-1-devnexen@gmail.com/
v2: https://lore.kernel.org/mptcp/20260421191337.58341-1-devnexen@gmail.com/

David Carlier (3):
  mptcp: propagate RECVERR sockopts to subflows
  mptcp: support MSG_ERRQUEUE on the parent socket
  selftests: mptcp: cover IP_RECVERR sockopt propagation

 net/mptcp/protocol.c                          | 123 ++++++++++++++---
 net/mptcp/sockopt.c                           | 129 ++++++++++++++++++
 .../selftests/net/mptcp/mptcp_sockopt.c       |  55 ++++++++
 3 files changed, 287 insertions(+), 20 deletions(-)


base-commit: 4464afe97dc56e817a23b730979cbc6fc48f1912
-- 
2.53.0