[PATCH mptcp-next v10 0/4] mptcp: MSG_ERRQUEUE support on the parent socket

[David Carlier <devnexen@gmail.com>]

This series lets MPTCP applications use poll(EPOLLERR) and
recvmsg(MSG_ERRQUEUE) on the parent socket to drain TX timestamps,
MSG_ZEROCOPY completion notifications and SO_EE_ORIGIN_LOCAL events
that are produced by the subflows, the same way they would on a plain
TCP socket. ICMP-derived errors stay on the subflow queue: the legacy
RECVERR ABI cannot convey their per-subflow peer identity, and they
are intended for a future MPTCP_RECERR channel.

Patch 1 factors the existing inet_flags subflow-propagation hard-coded
list into a mask, so subsequent patches can extend it without churn.

Patch 2 makes IP_RECVERR / IPV6_RECVERR (and the RFC4884 variants)
propagate to the subflows. The parent stores the bit so MPTCP-aware
helpers can branch on it.

Patch 3 splices subflow err-skbs onto the parent's sk_error_queue at
error-report time. MSG_ZEROCOPY completions are queued unconditionally
so a notification is never lost, mirroring tcp's
__msg_zerocopy_callback() which bypasses sk_rcvbuf for the same reason.
Timestamp and local events go through sock_queue_err_skb() and may be
dropped under rmem pressure, matching tcp's tx-timestamp path and
ip_icmp_error() / ipv6_icmp_error(). mptcp_recvmsg(MSG_ERRQUEUE)
forwards directly to inet_recv_error(), and mptcp_poll() advertises
EPOLLERR purely on the parent's sk_err / sk_error_queue, matching
tcp_poll().

Patch 4 is a selftest covering the propagation path.

Changes in v10 (addresses sashiko v9 review,
https://sashiko.dev/#/patchset/20260528055459.55133-1-devnexen@gmail.com):
 - patch 2/4: reject IPV6_RECVERR / IPV6_RECVERR_RFC4884 set/getsockopt
   on an AF_INET socket with -ENOPROTOOPT instead of routing a v4 socket
   into the v6 handler; matches plain TCP and removes a latent pinet6
   deref hazard. (sashiko v9, Medium)
 - patch 3/4: never drop MSG_ZEROCOPY completions. They are queued to
   the parent regardless of sk_rcvbuf, like tcp's
   __msg_zerocopy_callback(); previously a full parent err queue could
   drop them under receive-buffer pressure and leak the pinned userspace
   pages. (sashiko v9, High)

v9: https://lore.kernel.org/mptcp/20260528055459.55133-1-devnexen@gmail.com/

David Carlier (4):
  mptcp: sockopt: factor inet_flags propagation into a mask
  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                          |  68 ++++++--
 net/mptcp/sockopt.c                           | 151 +++++++++++++++---
 .../selftests/net/mptcp/mptcp_sockopt.c       |  55 +++++++
 3 files changed, 241 insertions(+), 33 deletions(-)


base-commit: 6ae41d6df6c12883277b2c9ab490b5c8b1a4fc85
--
2.53.0