Add/driver policy

[sohorx]

Hi,

In my understanding, currently to specify the same policy for a given driver we have to write it within the iface_default key for each interface name that bear this driver.

This pull request creates a new driver_default key that can duplicate a policy for each interface bearing the same driver name.

[julienfortin]

@sohorx can you provide an example of how this would be used?

btw pretty cool use of suppress I didn't know about that before :)

[sohorx]

sure ! :)

This is my use case:

{
  "dhcp": {
    "driver_defaults": {
      "qmi_wwan": {
        "dhcp-client": "udhcpc",
        "dhcp-wait": "no"
      }
    }
  }
}

I did some changes to make the module dhcp to handle multi-clients dhcp (which I'll make PR later on) and use this driver_defaults policy to set my client to be udhcpc for any 4g interfaces that use the qmi driver.

[sohorx]

btw, At first I wanted to make something like this:

        if (not ifname or not attr or not module_name):
            return None

        def dig(what, *args):
            return reduce(lambda d, k: d[k], args, what)

        driname = self._get_driver_name(ifname)
        policies = [
            [module_name, 'iface_defaults', ifname, attr],
            [module_name, 'driver_defaults', driname, attr],
            [module_name, 'defaults', attr],
        ]
        for args in policies:
            with suppress(TypeError, KeyError, IndexError):
                return dig(self.user_policy_array, *args)

        for args in policies:
            with suppress(TypeError, KeyError, IndexError):
                return dig(self.system_policy_array, *args)

        # could not find any system or user default so return Non
        return None

But that is maybe too much changes ;-)