Commits on Mar 15, 2024

1. [core] add MPTCP support …

   Multipath TCP (MPTCP), standardized in RFC8684 [1], is a TCP extension
   that enables a TCP connection to use different paths.
   Multipath TCP has been used for several use cases.
   On smartphones, Multipath TCP enables seamless handovers between
   cellular and Wi-Fi networks while preserving established connections.
   This use-case is what pushed Apple to use MPTCP since 2013 in multiple
   applications [2]. On dual-stack hosts, Multipath TCP enables the TCP
   connection to automatically use the best performing path,
   either IPv4 or IPv6. If one path fails, Multipath TCP automatically
   uses the other path. To benefit from MPTCP, both the client and the
   server have to support it.
   
   Multipath TCP is a backward-compatible TCP extension that is enabled by
   default on recent Linux distributions (Debian, Ubuntu, Redhat, ...).
   Multipath TCP is included in the Linux kernel since version 5.6 [3].
   To use Multipath TCP on Linux, a server application must explicitly
   enable it when creating the socket. No need to change anything else in
   the application. This is what the attached patch is doing.
   
   It is important to note that a MPTCP-enabled server continues to accept
   regular TCP connections that do not use the Multipath TCP extension
   without any performance impact.
   
   When a connection request is received, and is linked to a listening
   socket with MPTCP support, the kernel will simply check if MPTCP
   options are present. If not, the accepted socket will be a "plain" TCP
   one.
   
   This commit modifies the creation of sockets on Linux, trying to use
   Multipath TCP is available. If not, a plain TCP socket is created
   instead. A new option is now available: `server.network-mptcp`. This
   option is enabled by default. It seems important to enable this option
   by default on the server side, to let clients using MPTCP while not
   degrading performances when "plain" TCP is used. If the option is not
   enabled by default, it looks difficult to convince each administrator to
   enable it explicitly. This technology is mainly useful for the client
   side while it doesn't change much for the server side where no other
   configuration is needed.
   
   Link: https://www.rfc-editor.org/rfc/rfc8684.html [1]
   Link: https://www.tessares.net/apples-mptcp-story-so-far/ [2]
   Link: https://www.mptcp.dev [3]
   Co-developed-by: Maxime Dourov <mux99@live.be>
   Co-developed-by: Olivier Bonaventure <Olivier.Bonaventure@uclouvain.be>
   Co-developed-by: Matthieu Baerts <matttbe@kernel.org>
   Signed-off-by: Maxime Dourov (UCLouvain) <mux99@live.be>

   

   mux99 committed Mar 15, 2024
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