bearer mbim: ipv6_config set to dhcp when no ipv6 is available

[Aleksander Morgado]

>
> On Tue, Oct 09, 2018 at 10:27:41PM +0200, Reinhard Speyerer wrote:
> > for IPType IPv4v6 the IPType returned may be IPv4 or IPv6 instead of IPv4v6
> > in the case where PDP context activation is accepted by the network but it
> > returns a SM Cause 2 IE like this:
> > ...
>
> Yes, thank you. I have today confirmed this using a Sierra em7455.
> I configured IPv4v6 in the bearer. Using a Deutsche Telekom SIM it
> reported IPv4v6 and using a Vodafone SIM card it reported IPv4.
>
> Actually this is what I want, as it gives a clear indication if v6
> (or v4 or both) configuration should be attempted or not.
>
> Unfortunatly, as I wrote in my last mail ModemManger ignores this hint for
> the sake of supporting "broken" devices. The comment in mm-bearer-mbim.c
> mentiones a Vodafone Surfstick K5160.
>
> Maybe Aleksander or Dan have a suggestion on how to solve this while
> still maintaing support for the mentioned device.
>
> Could writing back the ip_type only if the configuration has ip_type
> Ipv4v6 be a solution? Is there a mechanism for device specifc quirks
> I could employ? Or should I maybe add a new attribute in the bearer
> which only reflects the ip_type reported back by the modem?
>

All the IPv6 management is a bit of a grey area for me :) I think that
the way to go here would be to implement correct support first (so any
solution you come up with is very welcome), and only then add
device-specific quirks, either by tagging them with some udev tags or
by trying to do a clean fallback if we can detect that the quirk is
needed in runtime. So, just forget about the comment in
mm-bearer-mbim.c initially, and then we'll see what to do.

-- 
Aleksander
https://aleksander.es