netdev - Re: Piggyback the final ACK of the three way TCP connection establishment with the data

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Date:	Fri, 23 Mar 2012 12:11:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	Vincent Li <vincent.mc.li@...il.com>, netdev@...r.kernel.org
Subject: Re: Piggyback the final ACK of the three way TCP connection
 establishment with the data

On Fri, 2012-03-23 at 12:03 -0700, Yuchung Cheng wrote:

> AFAICT the feature that Eric refers to is TCP Fast Open that I am
> still testing and have not yet submit to netdev.
> 

Nope, I was referring to actual linux code ;)

TFO will permit to send the DATA in the SYN packet, while Vincent only
asked to send it in the second packet the client sends to server.

> But one way to achieve that currently is doing a non-blocking connect
> then a blocking write.
> 
> I just tried this on 2.6 machine to a remote server
> 
> fcntl(sd, F_SETFL, fcntl(sd, F_GETFL, 0) | O_NONBLOCK);
> connect(sd, ...);
> fcntl(sd, F_SETFL, fcntl(sd, F_GETFL, 0) & ~O_NONBLOCK);
> sendto(sd, buf, buf, 0, ...);
> 
> The key is that the socket has to be in progress of connecting
> when application calls write/sendto(2). If you are testing on loopback,
> the connect might finish before sendto so this won't work.
> 




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