git: if_tap: Get rid of arpcom struct from tap_softc struct

[Sepherosa Ziehau]

There is IPv6 code too, assumes the existence of arpcom.  So I suggest
to revert this commit.  If you do want to get rid of arpcom, we will
have to make the stack change first; instead of starting from drivers.

IFP2AC() == cast ifnet to arpcom.

Thanks,
sephe

On Tue, Jul 17, 2018 at 4:57 PM, Aaron LI <aly at aaronly.me> wrote:
> Hi sephe,
>
> Thanks for pointing out the problem, but I don't understand it fully yet.
>
> Should I revert this commit, or continue to fix the related things?
>
> (1) The tap interface can be created correctly, and its MAC address is
> printed on console, so the 'ether_ifattach()', which calls
> 'ether_ifattach_bpf()', works as expected.  Is this you expected?
>
> (2) I think the problem you refer to is the following code in
> 'ether_ifattach_bpf()':
>
> 621    /*
> 622     * XXX Keep the current drivers happy.
> 623     * XXX Remove once all drivers have been cleaned up
> 624     */
> 625    if (lla != IFP2AC(ifp)->ac_enaddr)
> 626        bcopy(lla, IFP2AC(ifp)->ac_enaddr, ifp->if_addrlen);
>
> I don't understand how the 'IFP2AC(ifp)->ac_enaddr' works? On which
> conditions can we do 'struct type casting'?
>
> (3) As the above 'XXX' comments say, how to clean up the drivers?  Will it be
> complicated?  I can work on this.
>
> Cheers,
> --
> Weitian
>
>
> On Tue, 17 Jul 2018 16:16:58 +0800
> Sepherosa Ziehau <sepherosa at gmail.com> wrote:
>
>> You are breaking the ether_ifattach() of the tap interface; last time
>> I checked, this will break IPv6 stuff too, which assume the existence
>> of arpcom.
>>
>



-- 
Tomorrow Will Never Die