The TCP_MAXSEG socket option was not supported by MPTCP, mainly because
it has never been requested before. But there are still valid use-cases,
e.g. with HAProxy.

- Patch 1 is a small cleanup patch in the MPTCP sockopt file.

- Patch 2 expose some code from TCP, to avoid duplicating it in MPTCP.

- Patch 3 adds TCP_MAXSEG sockopt support in MPTCP.

- Patch 4 is not related to the others, it fixes a typo in a comment.

Note that the new TCP_MAXSEG sockopt support has been validated by a new
packetdrill script on the MPTCP CI:

  https://github.com/multipath-tcp/packetdrill/pull/161

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- Patch 2: Set the return value of tcp_sock_set_maxseg() to err.
- Patch 3: make mptcp_setsockopt_all_sf() returns only once.
- Link to v1: https://lore.kernel.org/r/20250716-net-next-mptcp-tcp_maxseg-v1-0-548d3a5666f6@kernel.org

---
Geliang Tang (3):
      mptcp: sockopt: drop redundant tcp_getsockopt
      tcp: add tcp_sock_set_maxseg
      mptcp: add TCP_MAXSEG sockopt support

moyuanhao (1):
      mptcp: fix typo in a comment

 include/linux/tcp.h  |  1 +
 net/ipv4/tcp.c       | 23 ++++++++++++++---------
 net/mptcp/protocol.c |  2 +-
 net/mptcp/protocol.h |  1 +
 net/mptcp/sockopt.c  | 33 +++++++++++++++++++++++++++++----
 5 files changed, 46 insertions(+), 14 deletions(-)
---
base-commit: d61f6cb6f6ef3c70d2ccc0d9c85c508cb8017da9
change-id: 20250716-net-next-mptcp-tcp_maxseg-e7702891080d

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

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sat, 19 Jul 2025 00:06:55 +0200 you wrote:
> The TCP_MAXSEG socket option was not supported by MPTCP, mainly because
> it has never been requested before. But there are still valid use-cases,
> e.g. with HAProxy.
> 
> - Patch 1 is a small cleanup patch in the MPTCP sockopt file.
> 
> - Patch 2 expose some code from TCP, to avoid duplicating it in MPTCP.
> 
> [...]

Here is the summary with links:
  - [net-next,v2,1/4] mptcp: sockopt: drop redundant tcp_getsockopt
    https://git.kernel.org/netdev/net-next/c/edd669057c56
  - [net-next,v2,2/4] tcp: add tcp_sock_set_maxseg
    https://git.kernel.org/netdev/net-next/c/51a62199a8aa
  - [net-next,v2,3/4] mptcp: add TCP_MAXSEG sockopt support
    https://git.kernel.org/netdev/net-next/c/51c5fd09e1b4
  - [net-next,v2,4/4] mptcp: fix typo in a comment
    https://git.kernel.org/netdev/net-next/c/154e56a77d81

You are awesome, thank you!
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