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From: David Miller on 17 Feb 2010 19:00
From: William Allen Simpson <william.allen.simpson(a)gmail.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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