netdev - Re: BSD 4.2 style TCP keepalives

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Message-ID: <alpine.DEB.2.00.1001070954240.3417@melkinpaasi.cs.helsinki.fi>
Date:	Thu, 7 Jan 2010 09:55:23 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>, nhorman@...driver.com
Subject: Re: BSD 4.2 style TCP keepalives

On Wed, 6 Jan 2010, David Miller wrote:

> From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Thu, 7 Jan 2010 02:34:51 +0200 (EET)
> 
> > On Wed, 6 Jan 2010, David Miller wrote:
> > 
> >> 3) tcp_data_queue() should make it to, and hit, this conditional:
> >> 
> >> 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
> >> 
> >>    which will schedule an ACK the same exact way we would if
> >>    tcp_sequence() rejected the sequence range.
> >> 
> >> So it's a mystery why we aren't responding to Windows 2000's
> >> BSD 4.2 style zero window probes.
> >> 
> >> Can someone please validate my analysis?
> > 
> > In 3) I don't see why we'd hit that one as peer's snd_una+1 would be 
> > larger than rcv_nxt.
> 
> Peer constructs keepalive packet using sequence [snd.una-1,snd.una],
> both of which are <= rcv_nxt

Right, I later realized that there was this !urgent but was already too 
much heading to zzz to correct it.


-- 
 i.