[Click] question for ipfilter

[Eddie Kohler]

negation_is_simple() is not used by IPFilter itself, but rather by other 
code that uses IPFilter.  It determines whether "!PRIMITIVE" is a valid 
primitive.  For instance, "!(proto == tcp)" can also be expressed as 
"proto != tcp".  However, "!(tcp port == 80)" has no simple negation, 
since its negation is the same as "(proto != tcp) || (proto == tcp && 
port != 80)".

Because of the TRANSP_FAKE_OFFSET stuff discussed in the last mail



wang houfen wrote:
> Hello,
> 
> What  functionality hat the following function negation_is_simple() and what for is the function used?
> 
> inline bool
> IPFilter::Primitive::negation_is_simple() const
> {
>   if (_type == TYPE_PROTO)
>     return true;
>   else if (_transp_proto >= 0)
>     return false;
>   else
>     return _type == TYPE_HOST || (_type & TYPE_FIELD) || _type == TYPE_IPFRAG;
> } 
> 
> 
> Why is packet_length = p->length() + TRANSP_FAKE_OFFSET - p->transport_header_offset() from IPFilter::length_checked_push(Packet *p)?
> 
> 
> Best Regards,
> Houfen
> 
> 
> 
> 
> 
> 
> 
> 
>  
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