netdev - Re: [PATCH net-next 3/3] net/tcp-fastopen: Add new API support

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Message-ID: <20170124184345.GF21921@1wt.eu>
Date:   Tue, 24 Jan 2017 19:43:45 +0100
From:   Willy Tarreau <w@....eu>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Yuchung Cheng <ycheng@...gle.com>, Wei Wang <tracywwnj@...il.com>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>
Subject: Re: [PATCH net-next 3/3] net/tcp-fastopen: Add new API support

On Tue, Jan 24, 2017 at 09:42:07AM -0800, Eric Dumazet wrote:
> On Tue, 2017-01-24 at 09:26 -0800, Yuchung Cheng wrote:
> 
> > >
> > > Do you think there's a compelling reason for adding a new option or
> > > are you interested in a small patch to perform the change above ?
> > I like the proposal especially other stack also uses TCP_FASTOPEN
> > https://msdn.microsoft.com/en-us/library/windows/desktop/ms738596(v=vs.85).aspx
> 
> 
> Problem is that might break existing applications that were using
> TCP_FASTOPEN before a connect() (it was a NOP until now)
> 
> I prefer we use a separate new option to be 100% safe, not adding
> regressions.
> 
> Only new applications, tested, will use this new feature at their risk.

That's indeed a good point. I Yuchung's comment above made me wonder
about application's portability but very few OSes will use this and in
the end it might be that portable applications will just add :

   #define TCP_FASTOPEN_CONNECT TCP_FASTOPEN

For other OSes and use TCP_FASTOPEN_CONNECT only for the connect() case.

Willy