Re: [PATCH RFC 2/3] netfilter: add ipv4 reverse path filter match

[Patrick McHardy <kaber@trash.net>]

On 30.08.2011 14:57, Florian Westphal wrote:
> Patrick McHardy <kaber@trash.net> wrote:
>> On 30.08.2011 14:41, Florian Westphal wrote:
>>> Patrick McHardy <kaber@trash.net> wrote:
>>>>> main drawback:
>>>>> - additional fib lookup to get oif (used as flow key in reverse lookup)
>>>>
>>>> As discussed during the workshop, we could just perform input routing
>>>> in the module to get the oif for free. That would require to take care
>>>> of statistics as currently done in ip_rcv_finish() though.
>>>
>>> Right.
>>> Any idea on how to solve the 'struct sk_buff *' (ip_route_input) vs.
>>> 'const struct sk_buff *' (matches) problem?
>>>
>>> We'd have to modify all the match signatures...
>>
>> Some modules already remove the const by casting it away, not
>> pretty, but works. Since the kernel doesn't assume strict aliasing
>> this also shouldn't cause any problems in the future. Alternatively
>> we can change the function signatures of course, although that would
>> be a bit unfortunate just for this special case.
> 
> Agreed, modifying the match function signature for this case would be
> sad.
> 
> I'll wait a couple of days and will send an updated version
> that uses the ugly cast + ip_route_input.

Regarding the statistic update, I'd suggest to move those to
a new function and call it from your module to avoid duplication
and possibly getting out of sync in the future.