netdev - Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build

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Message-Id: <20160923.080618.678103827885223586.davem@davemloft.net>
Date:   Fri, 23 Sep 2016 08:06:18 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     sowmini.varadhan@...cle.com
Cc:     jbenc@...hat.com, netdev@...r.kernel.org,
        hannes@...essinduktion.org, aduyck@...antis.com,
        daniel@...earbox.net, pabeni@...hat.com
Subject: Re: [PATCH net-next] net/vxlan: Avoid unaligned access in
 vxlan_build_skb()

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Thu, 22 Sep 2016 17:30:10 -0400

> On (09/22/16 01:52), David Miller wrote:
>> Alternatively we can do Alexander Duyck's trick, by pushing
>> the headers into the frag list, forcing a pull and realignment
>> by the next protocol layer.
> 
> What is the "Alexander Duyck trick" (hints about module or commit id,
> where this can be found, please)?
> 
> Is this basically about, e.g., putting the vxlanhdr in its own
> skb_frag_t, or something else?

Yes, and this way skb_header_pointer() is forced to do a memcpy.