linux-kernel - Re: [PATCH] tcp: splice as many packets as possible at once

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Message-Id: <20090119.125941.240930524.davem@davemloft.net>
Date:	Mon, 19 Jan 2009 12:59:41 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	w@....eu, jarkao2@...il.com, zbr@...emap.net, dada1@...mosbay.com,
	ben@...s.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH] tcp: splice as many packets as possible at once

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Mon, 19 Jan 2009 21:19:24 +1100

> On Sun, Jan 18, 2009 at 10:19:08PM -0800, David Miller wrote:
> > 
> > Actually, I see, the myri10ge driver does put up to
> > 64 bytes of the initial packet into the linear area.
> > If the IPV4 + TCP headers are less than this, you will
> > hit the corruption case even with the myri10ge driver.
> 
> I thought splice only mapped the payload areas, no?

And the difference between 64 and IPV4+TCP header len becomes the
payload, don't you see? :-)

myri10ge just pulls min(64, skb->len) bytes from the SKB frags into
the linear area, unconditionally.  So a small number of payload bytes
can in fact end up there.

Otherwise Willy could never have triggered this bug.
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