Re: size of a rule

[Ozgur AKAN <akan@aiqa.com>]

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Actually when I print the address of ipt_entry and subtract it from the 
next ipt_entry I can get the size of the rule but I am not sure if I am 
doing something wrong or right.

I still can not understand ((type *)0)->member.

Ozgur AKAN wrote:

> 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
>  
>


-- 
Ozgur Akan


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