add libvirt interface tcp tunnel support.

Useful when configuring Virtualized Switch topologies using Switch VMs like Cumulus
Linux.

vagrant network interface auto_config is disabled in the code. This may be
re-enabled in a future update, once it is better understood how to
auto configure these types of links. All guestOS ports, for now, that are
connected to a tcp tunnel are in a link down state.

TCP tunnels allow guest OSes to exchange STP and LLDP information as
if they are directly connected to each other.

This is not possible with the default virtual switch network mode.

Reference:
https://libvirt.org/formatdomain.html#elementsNICSTCP

README.md

@@ -213,7 +213,11 @@ Vagrant.configure("2") do |config|
 ## Networks
 
 Networking features in the form of `config.vm.network` support private networks
-concept.
+concept. It supports both the virtual network switch routing types and the point to
+point Guest OS to Guest OS setting using TCP tunnel interfaces.
+
+http://wiki.libvirt.org/page/VirtualNetworking
+https://libvirt.org/formatdomain.html#elementsNICSTCP
 
 Public Network interfaces are currently implemented using the macvtap driver. The macvtap
 driver is only available with the Linux Kernel version >= 2.6.24. See the following libvirt
@@ -221,14 +225,33 @@ documentation for the details of the macvtap usage.
 
 http://www.libvirt.org/formatdomain.html#elementsNICSDirect
 
+
 An examples of network interface definitions:
 
 ```ruby
-  # Private network
+  # Private network using virtual network switching
   config.vm.define :test_vm1 do |test_vm1|
     test_vm1.vm.network :private_network, :ip => "10.20.30.40"
   end
 
+  # Private network. Point to Point between 2 Guest OS using a TCP tunnel
+  # Guest 1
+  config.vm.define :test_vm1 do |test_vm1|
+    test_vm1.vm.network :private_network,
+          :libvirt__tcp_tunnel_type => 'server',
+          # default is 127.0.0.1 if omitted
+          # :libvirt__tcp_tunnel_ip => '127.0.0.1',
+          :libvirt__tcp_tunnel_port => '11111'
+
+  # Guest 2
+  config.vm.define :test_vm1 do |test_vm1|
+    test_vm1.vm.network :private_network,
+          :libvirt__tcp_tunnel_type => 'client',
+          # default is 127.0.0.1 if omitted
+          # :libvirt__tcp_tunnel_ip => '127.0.0.1',
+          :libvirt__tcp_tunnel_port => '11111'
+
+
   # Public Network
   config.vm.define :test_vm1 do |test_vm1|
     test_vm1.vm.network :public_network,
@@ -290,9 +313,19 @@ starts with 'libvirt__' string. Here is a list of those options:
 * `:libvirt__forward_device` - Name of interface/device, where network should
   be forwarded (NATed or routed). Used only when creating new network. By
   default, all physical interfaces are used.
+* `:libvirt_tcp_tunnel_type` - Set it to "server" or "client" to enable TCP
+  tunnel interface configuration. This configuration type uses TCP tunnels to
+  generate point to point connections between Guests. Useful for Switch VMs like
+  Cumulus Linux. No virtual switch setting like "libvirt__network_name" applies with TCP
+  tunnel interfaces and will be ignored if configured.
+* `:libvirt_tcp_tunnel_ip` - Sets the source IP of the TCP Tunnel interface. By
+  default this is `127.0.0.1`
+* `:libvirt_tcp_tunnel_port` - Sets the TCP Tunnel interface port that either
+  the client will connect to, or the server will listen on.
 * `:mac` - MAC address for the interface.
 * `:model_type` - parameter specifies the model of the network adapter when you create a domain value by default virtio KVM believe possible values, see the documentation for libvirt
 
+
 When the option `:libvirt__dhcp_enabled` is to to 'false' it shouldn't matter
 whether the virtual network contains a DHCP server or not and vagrant-libvirt
 should not fail on it. The only situation where vagrant-libvirt should fail

lib/vagrant-libvirt/action/create_network_interfaces.rb

@@ -36,7 +36,6 @@ module VagrantPlugins
           adapters = []
 
           # Vagrant gives you adapter 0 by default
-
           # Assign interfaces to slots.
           configured_networks(env, @logger).each do |options|
 
@@ -70,7 +69,6 @@ module VagrantPlugins
             @mac = iface_configuration.fetch(:mac, false)
             @model_type = iface_configuration.fetch(:model_type, @nic_model_type)
             template_name = 'interface'
-
             # Configuration for public interfaces which use the macvtap driver
             if iface_configuration[:iface_type] == :public_network
               @device = iface_configuration.fetch(:dev, 'eth0')
@@ -80,8 +78,18 @@ module VagrantPlugins
               template_name = 'public_interface'
               @logger.info("Setting up public interface using device #{@device} in mode #{@mode}")
               @ovs = iface_configuration.fetch(:ovs, false)
+            # configuration for tcp tunnel interfaces (p2p conn btwn guest OSes)
+            elsif iface_configuration.fetch(:tcp_tunnel_type, nil)
+              @tcp_tunnel_port = iface_configuration.fetch(:tcp_tunnel_port, nil)
+              raise Errors::TcpTunnelPortNotDefined if @tcp_tunnel_port.nil?
+              @tcp_tunnel_ip = iface_configuration.fetch(:tcp_tunnel_address, '127.0.0.1')
+              @type = iface_configuration.fetch(:tcp_tunnel_type)
+              @model_type = iface_configuration.fetch(:model_type, @nic_model_type)
+              template_name = 'tcp_tunnel_interface'
+              @logger.info("Setting up #{@type} tunnel interface using  #{@tcp_tunnel_ip} port #{@tcp_tunnel_port}")
             end
 
+
             message = "Creating network interface eth#{@iface_number}"
             message << " connected to network #{@network_name}."
             if @mac
@@ -144,6 +152,9 @@ module VagrantPlugins
               network[:type] = :dhcp
             end
 
+            # do not run configure_networks for tcp tunnel interfaces
+            next if options.fetch(:tcp_tunnel_type, nil)
+
             networks_to_configure << network
           end
 
@@ -163,6 +174,9 @@ module VagrantPlugins
 
         # Return network name according to interface options.
         def interface_network(libvirt_client, options)
+          # no need to get interface network for tcp tunnel config
+          return 'tcp_tunnel' if options.fetch(:tcp_tunnel_type, nil)
+
           if options[:network_name]
             @logger.debug "Found network by name"
             return options[:network_name]

lib/vagrant-libvirt/action/create_networks.rb

@@ -35,7 +35,8 @@ module VagrantPlugins
             # available, create it if possible. Otherwise raise an error.
             configured_networks(env, @logger).each do |options|
               # Only need to create private networks
-              next if options[:iface_type] != :private_network
+              next if options[:iface_type] != :private_network or
+                options.fetch(:tcp_tunnel_type, nil)
               @logger.debug "Searching for network with options #{options}"
 
               # should fix other methods so this doesn't have to be instance var

lib/vagrant-libvirt/errors.rb

@@ -106,6 +106,10 @@ module VagrantPlugins
         error_key(:activate_network_error)
       end
 
+      class TcpTunnelPortNotDefined < VagrantLibvirtError
+        error_key(:tcp_tunnel_port_not_defined)
+      end
+
       # Other exceptions
       class InterfaceSlotNotAvailable < VagrantLibvirtError
         error_key(:interface_slot_not_available)

lib/vagrant-libvirt/templates/tcp_tunnel_interface.xml.erb

@@ -0,0 +1,7 @@
+<interface type='<%= @type %>'>
+  <% if @mac %>
+  <mac address='<%= @mac %>'/>
+  <% end %>
+  <source address='<%=@tcp_tunnel_ip%>' port='<%= @tcp_tunnel_port %>'/>
+  <model type='<%=@model_type%>'/>
+</interface>

locales/en.yml

@@ -135,6 +135,8 @@ en:
         Error while removing network %{network_name}. %{error_message}.
       delete_snapshot_error: |-
         Error while deleting snapshot: %{error_message}.
+      tcp_tunnel_port_not_defined: |-
+        TCP tunnel port not defined.
 
     states:
       short_paused: |-