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 <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Co-developed-by: Peter Krystad <peter.krystad@linux.intel.com>
Signed-off-by: Peter Krystad <peter.krystad@linux.intel.com>
Co-developed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 0573ae75c3db..98ba22379117 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -28,6 +28,8 @@ struct mptcp_ext {
 
 #ifdef CONFIG_MPTCP
 
+void mptcp_init(void);
+
 /* move the skb extension owership, with the assumption that 'to' is
  * newly allocated
  */
@@ -70,6 +72,10 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
 
 #else
 
+static inline void mptcp_init(void)
+{
+}
+
 static inline void mptcp_skb_ext_move(struct sk_buff *to,
 				      const struct sk_buff *from)
 {
@@ -82,4 +88,14 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
 }
 
 #endif /* CONFIG_MPTCP */
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+int mptcpv6_init(void);
+#elif IS_ENABLED(CONFIG_IPV6)
+static inline int mptcpv6_init(void)
+{
+	return 0;
+}
+#endif
+
 #endif /* __NET_MPTCP_H */