netdev - Re: [PATCH 1/3] Support arbitrary initial TCP timestamps

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Message-Id: <20080217.233330.157255657.davem@davemloft.net>
Date:	Sun, 17 Feb 2008 23:33:30 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ggriffin.kernel@...il.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Support arbitrary initial TCP timestamps

From: Glenn Griffin <ggriffin.kernel@...il.com>
Date: Fri, 15 Feb 2008 09:47:08 -0800

> Introduce the ability to send arbitrary initial tcp timestamps that are not
> tied directly to jiffies.  The basic conecpt is every tcp_request_sock and
> tcp_sock now has a ts_off offset that represents the difference between
> tcp_time_stamp and the timestamp we send and expect to
> receive.
> 
> This has the advantage of not divulging system information (uptime)
> depending on the policy chosen for the initial timestamps.
> 
> A policy where ts_off is always set to zero should produce no change in
> behavior.  The policy implemented is not intended for real use, but just as
> a simple example.  A realistic example would probably be similar to the tcp
> init sequence generator.
> 
> Signed-off-by: Glenn Griffin <ggriffin.kernel@...il.com>

Adding yet another member to the already bloated tcp_sock structure to
implement this is too high a cost.

I would instead prefer that there be some global random number
calculated when the first TCP socket is created, and use that as a
global offset.  You can even recompute it every few hours if you
like.

We do similar things already elsewhere.
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