From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH v2] net: bridge: add compile-time assert for cb struct
 size
Date: Tue, 03 Mar 2015 15:28:47 +0100
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To: David Laight <David.Laight@ACULAB.COM>,
	'Florian Westphal' <fw@strlen.de>,
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On 03/03/2015 02:50 PM, David Laight wrote:
...
>> +	BUILD_BUG_ON(sizeof(struct br_input_skb_cb) > FIELD_SIZEOF(struct sk_buff, cb));
>> +
>
> What about using something based on:
> #define GET_CB(skb, type) ((type *)((skb)->cb + (sizeof (char[(sizeof (type) <= sizeof (skb->cb)) ? 1 : -1] - 1)))
> to access skb->sb?

That would require to change all skb->cb[] call-sites everywhere.

Besides that, this macro is also buggy, my totally untrained lisp-eye tells
me that you got your brackets wrong.

Cheers,
Daniel