netdev - Re: [PATCH] TCP: Add seq and ack numbers to TCP

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Message-ID: <396556a20807091102n5bb061daw91f41512faa8474@mail.gmail.com>
Date:	Wed, 9 Jul 2008 11:02:54 -0700
From:	"Adam Langley" <agl@...erialviolet.org>
To:	"Stephen Hemminger" <stephen.hemminger@...tta.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] TCP: Add seq and ack numbers to TCP_INFO

On Wed, Jul 9, 2008 at 10:49 AM, Stephen Hemminger
<stephen.hemminger@...tta.com> wrote:
> Of what possible use is this to an application? I worry that applications would
> come to expect or use certain characteristics of the network and TCP which
> would be broken by later changes.

Well, when you consider what else is in tcp_info (window scaling, SACK
info, MTU, RTT, reorder detection), the sequence numbers seem
positively pedestrian.

There are a bunch of crazy reasons why userspace might be interested
in the seq/ack numbers: handing connections between hosts, checking
the backlog, analyzing the RNG strength of remote hosts etc. All
experimental crap to be sure, but it's very handy in those
experiments. I used a very similar patch when doing some of the very
early basic on backlogs that Jerry Chu has taken up now.

And sequence numbers are pretty fundamental to TCP. Certainly much
more so than much of the other stuff that we're currently happy to
export with sufficient warnings.

AGL

-- 
Adam Langley agl@...erialviolet.org http://www.imperialviolet.org
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