MPTCP support

[matttbe]

Hello,

Thank you for developing and maintaining this kernel feature!

It would be great if it would be possible to have the possibility to use an MPTCP socket, and benefit from it to use multiple paths at the same time or one after the other.

On the userspace side, it is easy to switch from TCP to MPTCP: simply switching from IPPROTO_TCP to IPPROTO_MPTCP when creating the socket (doc). On the kernelspace side, I didn't look at the new OVPN driver, but hopefully it shouldn't be too different from the TCP interface :)

Previous discussions about that:

• bug when using mptcp kernel ovpn-dco#60
• when using openvpn in tcp with dco, we have a bug multipath-tcp/mptcp_net-next#479
• https://lore.kernel.org/netdev/813d75bf-1d7f-472b-967f-27ab8f9d4759@kernel.org/

[ordex]

Hey @matttbe thanks for raising this!
The transport socket is first created in userspace and then passed to the ovpn driver.
If sending/receiving APIs is transparent to MPTCP, then it may just be as easy as switching from IPPROTO_TCP to IPPROTO_MPTCP in userspace.

[matttbe]

Hi @ordex,

Thank you for your reply!

I see, that's good, so the API is ready for the userspace. On the kernel side, I guess socket.c will need some small adaptations for IPPROTO_MPTCP, but not sure about tcp.c :)

[ordex]

Hi @matttbe in tcp.c we use the stream parser API/abstraction for receiving packets.
Do you know if that already supports MPTCP? It is also used by espintcp.c for IPSec.

[matttbe]

Hi @matttbe in tcp.c we use the stream parser API/abstraction for receiving packets. Do you know if that already supports MPTCP? It is also used by espintcp.c for IPSec.

@ordex oops, sorry, I missed your question.

I never used the Stream Parser API (from net/strparser, right?), but after a quick look, I don't see anything TCP specific, and it seems to consume data a bit like a userspace app would do. So I guess it should be fine. If not, I'm sure this can be fixed :)

[Neustradamus]

It will be nice to have this feature!