Resubmit as v2 RFC to get some feedback before net-next opens up again.
Only minor changes (see below).

This patchset introduces a generic framework for handling TCP-options.

TCP-options like TCP_MD5 and SMC are rather rare use-cases, but their
implementation is rather intrusive to the TCP-stack. Other, more recent
TCP extensions like TCP-crypt, MPTCP or TCP-AO would make this situation
even worse.

This new framework allows to add these TCP-options in a modular way. Writing,
reading and acting upon these options is done through callbacks that get
registered to a TCP-socket. A TCP-socket has a list of "extra" TCP-options
that it will use.

We make TCP-SMC and TCP-MD5SIG adopt this new framework. As can be seen, there
is now no more TCP-SMC code in the TCP-files and the TCP-MD5 code has been
reduced to a bare minimum.

This patchset is admittedly rather big, but we wanted to show where the
framework will lead to and what it enables. Suggestions as to how to better
structure the patchset is appreciated.

There is still work to be done to more efficiently check for extra TCP options
in performance-sensitive code paths. A rate-limited static key would nearly
eliminate overhead if no extra TCP options are in use system-wide, or a flag
in a likely-hot cache line could work well.

For now we opted for a simple if (unlikely(!hlist_empty(...)) check.

Feedback is very welcome!

Mat & Christoph

v1 -> v2:
        * Some minor fixes thanks to the buildbot when certain configs
          are disabled (Patch 5 and 12)
        * Add spdx-header in the new files (Patch 11)
        * Added Ivan Delande to the CC-list as he did some TCP-MD5
          changes in the past.

Christoph Paasch (13):
  tcp: Write options after the header has been fully done
  tcp: Pass sock and skb to tcp_options_write
  tcp: Allow tcp_fast_parse_options to drop segments
  tcp_smc: Make smc_parse_options return 1 on success
  tcp_smc: Make SMC use TCP extra-option framework
  tcp_md5: Don't pass along md5-key
  tcp_md5: Detect key inside tcp_v4_send_ack instead of passing it as an
  tcp_md5: Detect key inside tcp_v6_send_response instead of passing it
    as an argument
  tcp_md5: Check for TCP_MD5 after TCP Timestamps in
  tcp_md5: Move TCP-MD5 code out of TCP itself
  tcp_md5: Use tcp_extra_options in output path
  tcp_md5: Cleanup TCP-code
  tcp_md5: Use TCP extra-options on the input path

Mat Martineau (1):
  tcp: Register handlers for extra TCP options

 drivers/infiniband/hw/cxgb4/cm.c |    2 +-
 include/linux/inet_diag.h        |    1 +
 include/linux/tcp.h              |   43 +-
 include/linux/tcp_md5.h          |   40 ++
 include/net/inet_sock.h          |    3 +-
 include/net/tcp.h                |  213 +++---
 net/ipv4/Makefile                |    1 +
 net/ipv4/syncookies.c            |    6 +-
 net/ipv4/tcp.c                   |  391 ++++++++---
 net/ipv4/tcp_diag.c              |   81 +--
 net/ipv4/tcp_input.c             |  137 ++--
 net/ipv4/tcp_ipv4.c              |  556 ++--------------
 net/ipv4/tcp_md5.c               | 1359 ++++++++++++++++++++++++++++++++++++++
 net/ipv4/tcp_minisocks.c         |   75 +--
 net/ipv4/tcp_output.c            |  182 +----
 net/ipv6/syncookies.c            |    6 +-
 net/ipv6/tcp_ipv6.c              |  390 ++---------
 net/smc/af_smc.c                 |  190 +++++-
 18 files changed, 2228 insertions(+), 1448 deletions(-)
 create mode 100644 include/linux/tcp_md5.h
 create mode 100644 net/ipv4/tcp_md5.c


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