mptcp: Add MPTCP socket stubs

Implements the infrastructure for MPTCP sockets.

MPTCP sockets open one in-kernel TCP socket per subflow. These subflow
sockets are only managed by the MPTCP socket that owns them and are not
visible from userspace. This commit allows a userspace program to open
an MPTCP socket with:

  sock = socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);

The resulting socket is simply a wrapper around a single regular TCP
socket, without any of the MPTCP protocol implemented over the wire.

Co-developed-by: Florian Westphal <[email protected]>
Signed-off-by: Florian Westphal <[email protected]>
Co-developed-by: Peter Krystad <[email protected]>
Signed-off-by: Peter Krystad <[email protected]>
Co-developed-by: Matthieu Baerts <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>
Co-developed-by: Paolo Abeni <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Mat Martineau <[email protected]>
Signed-off-by: Christoph Paasch <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 5b5260103b65..60068ffde1d9 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -2163,9 +2163,16 @@ int __init tcpv6_init(void)
 	ret = register_pernet_subsys(&tcpv6_net_ops);
 	if (ret)
 		goto out_tcpv6_protosw;
+
+	ret = mptcpv6_init();
+	if (ret)
+		goto out_tcpv6_pernet_subsys;
+
 out:
 	return ret;
 
+out_tcpv6_pernet_subsys:
+	unregister_pernet_subsys(&tcpv6_net_ops);
 out_tcpv6_protosw:
 	inet6_unregister_protosw(&tcpv6_protosw);
 out_tcpv6_protocol: