nmstate: Nmstate should ignore interface with `state: unknown` also

Hi, as promised I’m going to give some hints about where to look at. Sorry for the delay.

First, all the input in yaml format is parsed and converted it to Rust structures. This is done by the crate (library) serde. In most cases, the way to parse the different structures is indicated only with macro annotations like #[serde(...)] in the Rust structs itself. Other times, more rarely, we need to implement the Deserialize trait if the yaml deserialization is more complex.

The request in this issue is to ignore interfaces that in the yaml has state: unknown, that’s what NO_OP means (no operation). We already allow it with state: ignore, but we want to accept “unknown” too. Am I correct on this, @cathay4t?

The field “state” is part of the items of the list “interfaces”. So, we can deduce that each of the elements is parsed to the Rust type Interface. Actually, Interface can be of different types like EthernetInterface, LinuxBridgeInterface, etc. If we look to some of those types, we see that all them contains a field of the type BaseInterface.

This BaseInterface is the Rust structure that contains the information common to all interface types, “state” among them. Take a look to this BaseInteface type and see how you can do to accept “state: unknown” for it and do what is requested in this issue.

You can probably ignore the warning about the unsupported NetworkManager version. If you can update to a newer Ubuntu it will disappear, though.

You can use any of them. If you don’t have any preference, I recomend you Fedora. But if you are already familiar with Ubuntu, you can use it too.