From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v2 net-next] net: filter: export pkt_type_offset() helper
Date: Wed, 03 Sep 2014 19:05:48 -0700
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Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
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	Eric Dumazet <edumazet@google.com>,
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To: Hannes Frederic Sowa <hannes@stressinduktion.org>
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On Thu, 2014-09-04 at 03:25 +0200, Hannes Frederic Sowa wrote:

> Can't we add an address marker to struct sk_buff?
> 
> Several possibilities are available:
> 
> ptrdiff_t pkt_type_offset[0]  before the pkt_type flags field
> 
> If one wants to make it more expressive:
> typedef struct {} mark_struct_offset;
> and add
> mark_struct_offset pkt_type_offset;
> at appropriate places
> 
> Or maybe an anonymous union?
> 
> pkt_type_offset would become a simple offsetof(struct sk_buff,
> pkt_type_offset) then and there is no need for BUG_ON then.


You can try, and make sure this works on all gcc compilers, even the one
Andrew Morton uses.

And of course, you need to not introduce holes doing so.