netdev - Re: [PATCH] tcp: accept socket after TCP_DEFER

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Date:	Mon, 19 Oct 2009 22:04:09 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Julian Anastasov <ja@....bg>
CC:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: accept socket after TCP_DEFER_ACCEPT period

Julian Anastasov a écrit :
> 	Willy Tarreau and many other folks in recent years
> were concerned what happens when the TCP_DEFER_ACCEPT period
> expires for clients which sent ACK packet. They prefer clients
> that actively resend ACK on our SYN-ACK retransmissions to be
> converted from open requests to sockets and queued to the
> listener for accepting after the deferring period is finished.
> Then application server can decide to wait longer for data
> or to properly terminate the connection with FIN if read()
> returns EAGAIN which is an indication for accepting after
> the deferring period. This change still can have side effects
> for applications that expect always to see data on the accepted
> socket. Others can be prepared to work in both modes (with or
> without TCP_DEFER_ACCEPT period) and their data processing can
> ignore the read=EAGAIN notification and to allocate resources for
> clients which proved to have no data to send during the deferring
> period. OTOH, servers that use TCP_DEFER_ACCEPT=1 as flag (not
> as a timeout) to wait for data will notice clients that didn't
> send data for 3 seconds but that still resend ACKs.
> Thanks to Willy Tarreau for the initial idea and to
> Eric Dumazet for the review and testing the change.
> 
> Signed-off-by: Julian Anastasov <ja@....bg>
> ---
> 
> diff -urp v2.6.31/linux/net/ipv4/tcp_minisocks.c linux/net/ipv4/tcp_minisocks.c
> --- v2.6.31/linux/net/ipv4/tcp_minisocks.c	2009-09-11 10:27:17.000000000 +0300
> +++ linux/net/ipv4/tcp_minisocks.c	2009-10-16 10:29:19.000000000 +0300
> @@ -641,8 +641,8 @@ struct sock *tcp_check_req(struct sock *
>  	if (!(flg & TCP_FLAG_ACK))
>  		return NULL;
>  
> -	/* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
> -	if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
> +	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
> +	if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
>  	    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
>  		inet_rsk(req)->acked = 1;
>  		return NULL;
> --

Acked-by: Eric Dumazet <eric.dumazet@...il.com>

Thanks Julian
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