Previously, netdev units for network interfaces defined in the nixos
configurations would bindTo the systemd device unit of the interface if
not in a container.
In situations where you switch to a new nixos configration with changes
to network-setup.service (like nameservers) and have stacked interfaces
like vlans on a bond, it would fail to propagate restarts to the netdevs
correctly resulting with broken networking. The bond would be present
but no vlan interfaces rendering the machine unreachable.
My fear is that the udev events fail to propagate correctly while a systemd
transaction that is also restarting the triggered netdev service is running.
This commit changes this behaviour so netdev services bindTo other netdev
services if present and otherwise fall back to the previous behaviour.
We also noticed that stacked interfaces would sometimes seemingly be stopped
in the wrong order. For instance in the above example, the bond interface
would be deleted before the vlan interfaces resulting in the vlan interfaces
not being present when their service is being stopped. This would cause the
systemd transaction to fail and thus break networking. Their postStop hooks
are now allowed to fail as we have reached the desired state.
76a3c30471