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From: Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [RFC] net/hsr: Add support for IEC 62439-3 High-availability
 Seamless Redundancy
Date: Tue, 10 Apr 2012 18:28:47 -0700
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> 3) My feeble suggestion to cast icmp_hdr() to (char *) is of course even worse (it doesn't
> even avoid the erroneous cast in the first place).
> 
> So what do we do?
> 

Reading Documentation/unalgined-memory-access.txt suggests that you
probably should copy the skb before passing up the stack (if necessary).
That is safe (but slightly slower).