linux-kernel - Re: [PATCH v4 4/7] tcp: input header length, prediction, and timestamp bugs

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Message-Id: <20100217.155030.110521237.davem@davemloft.net>
Date:	Wed, 17 Feb 2010 15:50:30 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	william.allen.simpson@...il.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	akpm@...ux-foundation.org, andi@...stfloor.org
Subject: Re: [PATCH v4 4/7] tcp: input header length, prediction, and
 timestamp bugs

From: William Allen Simpson <william.allen.simpson@...il.com>
Date: Sun, 14 Feb 2010 01:21:35 -0500

> Don't use output calculated tp->tcp_header_len for input decisions.
> While the output header is usually the same as the input (same options
> in both directions), that's a poor assumption. In particular, Sack
> will
> be different. Newer options are not guaranteed.

And when SACK is present, tp->tcp_header_len will not match, and
therefore we won't do the header prediction fast path, what is what we
want.

And, SACK presence doesn't change tp->tcp_header_len on transmit.

Therefore, I see no need at all for this change.
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