[PATCH net-next v2 0/4] mptcp: add TCP_MAXSEG sockopt support

[Matthieu Baerts (NGI0)]

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@xxxxxxxxxx>
---
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@xxxxxxxxxx

---
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@xxxxxxxxxx>