notify the application (userspace) when a subflow is added/removed

[matttbe]

Maybe using cmsg?

A userspace app would get a poll notification when something has changed with a socket (fd) it owns. If needed, another syscall could be used to retrieve the current status.

[geliangtang]

@matttbe @fw-strlen Could Florian's commit "mptcp: add netlink event support" close this issue?

[matttbe]

@geliangtang no, this is different I think.

Clearly, we are lacking some description here but if I remember well, the idea was to get a notification via the fd without having to subscribe to events of all connections. The userspace could get a poll notification when something subflows are added or removed and it could then get the status with another request (e.g. a new getsockopt)