Comment 3 for bug 1806969

I'm working on a patch to fix this, but I do have one concern.

Consider a constraint string such as:

    interfaces='eth0:space=foo;eth1:space=bar,mode=unconfigured'

In this case, MAAS will not know which subnet to link eth1 to. So you will end up with an interface on the correct L2 space, but with no knowledge of which subnet to link it to. Therefore you end up with a "disconnected" interface on no subnet.

I feel like, from the bug description, you would prefer a link to the subnet, but with an unconfigured IP mode. There are a few things I can think of that we could do to reduce the ambiguity, including one or more of the following:

 - Require the user to specify the desired subnet in the constraint string
 - Make it so that specifying `mode=unconfigured` chooses an arbitrary subnet on the `bar` space.
 - Add another mode constraint such as `mode=disconnected` to specify that the interface should not be linked to a subnet at all, even if one is specified or implied by the constraints.

Thoughts?