size of a rule

[Ozgur AKAN <akan@aiqa.com>]

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Hi,
I am trying to find the size of a rule in memory.

const struct ipt_entry *e;

sizeof (*e) is equal to 112 always. But the size of rule should be 
different because we can give different parameters to each rule. (I 
guess that this is the size of the header-like place)

So I looked at the source of libiptc and found this in linux_list.h 
while searching for the size value.

#define list_entry(ptr, type, member) \
        ((type *) ( (char *)(ptr)-(unsigned long)(&((type *)0)->member) ) )

What is the meaning of ((type *)0)->member ? I can not understand the 
part with 0.  

thanks,
-- 
Ozgur Akan


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