Merge branch 'mptcp-dss-checksums'

Merge branch 'mptcp-dss-checksums'

Mat Martineau says:

====================
mptcp: DSS checksum support

RFC 8684 defines a DSS checksum feature that allows MPTCP to detect
middlebox interference with the MPTCP DSS header and the portion of the
data stream associated with that header. So far, the MPTCP
implementation in the Linux kernel has not supported this feature.

This patch series adds DSS checksum support. By default, the kernel will
not request checksums when sending SYN or SYN/ACK packets for MPTCP
connections. Outgoing checksum requests can be enabled with a
per-namespace net.mptcp.checksum_enabled sysctl. MPTCP connections will
now proceed with DSS checksums when the peer requests them, whether the
sysctl is enabled or not.

Patches 1-5 add checksum bits to the outgoing SYN, SYN/ACK, and data
packet headers. This includes calculating the checksum using a range of
data and the MPTCP DSS mapping for that data.

Patches 6-10 handle the checksum request in the SYN or SYN/ACK, and
receiving and verifying the DSS checksum on data packets.

Patch 11 adjusts the MPTCP-level retransmission process for checksum
compatibility.

Patches 12-14 add checksum-related MIBs, the net.mptcp.checksum_enabled
sysctl, and a checksum field to debug trace output.

Patches 15 & 16 add selftests.

The series is slightly longer than the preferred 15-patch limit that
patchwork warns about. I do try to stay below that whenever possible -
this series does implement one feature and is, I think, cohesive enough
to justify keeping it together. If it's at all problematic please let me
know!

A trivial merge conflict with net/master is introduced in patch 15: a
commit in net/master removes a couple of nearby lines of code.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>