Re: [PATCH mptcp-next v12 0/4] mptcp: MSG_ERRQUEUE support on the parent socket

Hi David, Paolo,

On 30/07/2026 09:12, David Carlier wrote:
> This series lets MPTCP applications use poll(EPOLLERR) and
> recvmsg(MSG_ERRQUEUE) on the parent socket to drain TX timestamps
> through the standard inet ABI, 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 splices subflow err-skbs onto the parent's sk_error_queue at
> error-report time. All forwarded events go through sock_queue_err_skb(),
> which re-homes skb->sk onto the parent and charges sk_rmem_alloc, so the
> parent's error queue stays bounded by sk_rcvbuf and is 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 2 factors the existing inet_flags subflow-propagation hard-coded
> list into a mask, so the next patch can extend it without churn.
> 
> Patch 3 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 4 is a selftest covering the propagation path.
> 
> Changes in v12 (addresses Paolo's v11 review):
>  - reordered the series so the core MSG_ERRQUEUE infrastructure lands
>    first, before the sockopt plumbing that exposes it to user space.
>    The former patch 3/4 is now 1/4.
>  - 1/4: narrow mptcp_errqueue_skb_forwardable() to
>    SO_EE_ORIGIN_TIMESTAMPING. SO_EE_ORIGIN_ZEROCOPY and
>    SO_EE_ORIGIN_LOCAL events cannot be generated on an MPTCP parent
>    today, so the helper only needs extending if and when they can be.
>  - 1/4: trim the block comment above sock_queue_err_skb() and the
>    matching changelog paragraphs, now redundant with the narrower
>    filter.
>  - 2/4: reverse christmas tree declaration ordering in
>    sync_socket_options().
>  - dropped the Suggested-by: Paolo Abeni tags from patches 1-3.
>  - rebased on current export.
Thank you for the v12 and for the previous reviews!

I just applied this series with Paolo's ACK, as I understood the v11 was
good for him, and you applied the last requests he had. I hope that's
OK, I can always fix that later.

Note that I also fixed a few checkpatch issues, not to get in troubles
when upstreaming these patches later.

New patches for t/upstream:
- d1c8339c6464: mptcp: support MSG_ERRQUEUE on the parent socket
- b10c2f76fdcf: mptcp: sockopt: factor inet_flags propagation into a mask
- 36a365e46b58: mptcp: propagate RECVERR sockopts to subflows
- a2f437ee45ab: selftests: mptcp: cover IP_RECVERR sockopt propagation
- Results: e5730411f842..e486d89a0699 (export)

Tests are now in progress:

- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/0565f7c5598354965c1a391e4f96fe5d2f1c09a1/checks

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