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Date: Fri, 10 Oct 2014 14:15:59 -0400 (EDT)
From: David Miller <davem@...emloft.net>
To: alexander.duyck@...il.com
Cc: alexander.h.duyck@...hat.com, eric.dumazet@...il.com,
David.Laight@...LAB.COM, netdev@...r.kernel.org
Subject: Re: [PATCH] flow-dissector: Fix alignment issue in
__skb_flow_get_ports
From: Alexander Duyck <alexander.duyck@...il.com>
Date: Fri, 10 Oct 2014 11:02:04 -0700
> On 10/10/2014 10:58 AM, David Miller wrote:
>> From: Alexander Duyck <alexander.h.duyck@...hat.com>
>> Date: Fri, 10 Oct 2014 09:50:17 -0700
>>
>>> If I just use get_unaligned that is pretty easy in terms of cleanup
>>> for the ports and IPv4 addresses, the IPv6 will still be a significant
>>> hurdle to overcome though.
>> Actually, it's not that simple.
>>
>> When the compiler sees things like "th->doff" it will load the 32-bit
>> word that 4-bit field contains and extract the value using shifts and
>> masking.
>>
>> So we might need to sprinkle a "attribute((packed))" here and there
>> to make it work.
>
> I'll do some digging. I know I had this working in igb/ixgbe before so
> I probably just need to add a few small tweaks to resolve the remaining
> issues for v4 of the patch.
Your original code works because you do things like "byte[12] & 0xf0" to
extract these fields.
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