Use libvirt to query host physical devices (#1550)

Request the list of physical devices from libvirt when performing
config validation. This ensures remote instances using bridges will get
the correct list of devices as well as be alerted when the device needed
does not exist.

Fixes issue introduced with #1499

lib/vagrant-libvirt/config.rb

@@ -1067,8 +1067,9 @@ module VagrantPlugins
 
           # only interested in public networks where portgroup is nil, as then source will be a host device
           if type == :public_network && opts[:portgroup] == nil
-            if !host_devices.include?(opts[:dev])
+            devices = host_devices(machine)
-              errors << "network configuration #{index} for machine #{machine.name} is a public_network referencing host device '#{opts[:dev]}' which does not exist, consider adding ':dev => ....' referencing one of #{host_devices.join(", ")}"
+            if !devices.include?(opts[:dev])
+              errors << "network configuration #{index} for machine #{machine.name} is a public_network referencing host device '#{opts[:dev]}' which does not exist, consider adding ':dev => ....' referencing one of #{devices.join(", ")}"
             end
           end
         end
@@ -1210,11 +1211,9 @@ module VagrantPlugins
         end
       end
 
-      def host_devices
+      def host_devices(machine)
         @host_devices ||= begin
-          require 'socket'
+          machine.provider.driver.connection.client.list_all_interfaces().map { |iface| iface.name }.uniq.select do |dev|
-
-          Socket.getifaddrs.map { |iface| iface.name }.uniq.select do |dev|
             dev != "lo" && !@host_device_exclude_prefixes.any? { |exclude| dev.start_with?(exclude) }
           end
         end

spec/unit/config_spec.rb

@@ -635,13 +635,15 @@ describe VagrantPlugins::ProviderLibvirt::Config do
     end
 
     context 'with public_network defined' do
+      let(:libvirt_client)  { instance_double(::Libvirt::Connect) }
       let(:host_devices) { [
-        instance_double(Socket::Ifaddr),
+        instance_double(Libvirt::Interface),
-        instance_double(Socket::Ifaddr),
+        instance_double(Libvirt::Interface),
       ] }
       before do
         machine.config.vm.network :public_network, dev: 'eth0', ip: "192.168.2.157"
-        expect(Socket).to receive(:getifaddrs).and_return(host_devices)
+        expect(machine).to receive_message_chain('provider.driver.connection.client').and_return(libvirt_client)
+        expect(libvirt_client).to receive(:list_all_interfaces).and_return(host_devices)
         expect(host_devices[0]).to receive(:name).and_return('eth0')
         expect(host_devices[1]).to receive(:name).and_return('virbr0')
       end