Patching ng_iface to allow setting the MTU via netgraph API

[Andreas Kempe]

On 2018-10-10 22:33, Eugene Grosbein wrote:
> However, this patch does not seem quite right to me. It may serve your needs
> but it is incomplete in general case. You see, change in MTU should affect not only
> interface itself, it should also alter routing table and "interface link" routes
> that also have MTU attribute that is used for handling outgoing IP packets utilizing such routes.
>

I am no expert on FreeBSD internals. I was wondering about this exact
aspect and was hoping to get feedback just like this.

> Why do you want to replicate this at NETGRAPH level?
> ng_iface(4) was created to be generic network interface to NOT duplicate such things.
>
After reading this, I went back and read the manual to ifconfig again.
My wish is based on a misconception. I thought that the point-to-point
vs. broadcast setting was general for all interfaces and could be
readily set by using ifconfig ptp. As there was already duplication on
that setting, I didn't see any real issue with setting the MTU via
netgraph as well. Realising this is not the case has made me see that my
idea isn't a great one.

At least I know how to submit a patch in the future if I get actually
well thought out ideas.

Thank you for the feedback!
// Andreas Kempe