Re: [MPTCP] [RFC PATCH mptcp-next v2 1/8] mptcp: add skeleton to sync msk socket options to subflows

[Florian Westphal <fw@strlen.de>]

Paolo Abeni <pabeni@redhat.com> wrote:
> On Thu, 2021-03-25 at 15:06 +0100, Florian Westphal wrote:
> > Sorry, I am not following.
> > 
> > The ssk (s2 msk->first) has ssk->seq 1, s2 msk has 2, so this would be
> > synced again on completion.
> > 
> > I don't understand how s1 and s2 are related.
> > This is too complicated for me :(
> 
> s1 is an msk listener socket. It will get 2 setsockopt() syscall, so
> s1->sockopt_seq == 2.
> 
> Even s2->sockopt_seq == 2, as you noted.
> 
> If we copy msk->sockopt_seq into ssk->sockopt_seq, any additional MPJ
> subflow joining s2 created after the above syscalls sequence, will
> get sockopt_seq == 2, (inherited by s1->sockopt_seq), so will not be
> synched, even if synchronization will be needed.
> 
> Not sure if the above is less confusing ?!?

I would expect the new join ssk to have a 0 sequence number.

> > > Instead, if we set sockopt_seq to some socket status related value
> > > after every setsockopt(), s2->sockopt_seq and s1->sockopt_seq will be
> > > different and we will sync later MPJ subflows.
> > 
> > What is a 'socket status related value'?
> 
> I mean something that changes when 'sk->sk_state' changes. Even plain
> 'sk->sk_state'.

So instead of sync if msk->seq != ssk->seq we sync if
sk->sk_state != ssk->sk_state?

I don't understand how that works.

We might try to discuss this in the meeting, perhaps that would help?