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Date: Fri, 10 Oct 2014 08:29:33 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: alexander.h.duyck@...hat.com
Cc: David Laight <David.Laight@...LAB.COM>,
David Miller <davem@...emloft.net>,
"alexander.duyck@...il.com" <alexander.duyck@...il.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] flow-dissector: Fix alignment issue in
__skb_flow_get_ports
On Fri, 2014-10-10 at 08:14 -0700, Alexander Duyck wrote:
> I think you might be coming to this a little late. The igb and ixgbe
> drivers had been working this way for a long time. We did a memcpy to
> move the headers from the page and into the skb->data at an aligned
> offset. In order to determine the length to memcpy we had a function
> that could walk through the DMA aligned data to get the header length.
> The function for that was replaced with the __skb_flow_dissect as it was
> considered a duplication of code with the flow_dissection functions.
> However that is obviously not the case now that we are hitting these
> alignment issues.
>
> The question I have in all this is do I push forward and make
> __skb_flow_dissect work with unaligned accesses, or do I back off and
> put something equivilent to igb/ixgbe_get_headlen functions in the
> kernel in order to deal with the unaligned accesses as they had no
> issues with them since they were only concerned with getting the header
> length and kept all accesses 16b aligned.
>
I see nothing wrong dealing with unaligned accesses, as these helpers
are nop on x86 or CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y arches.
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