Add support for configuring memballoon-related settings (#1083)

Allow configuration of various memballoon-related settings. It was 
discovered that it may be needed to be able to control the memballoon's 
PCI slot/bus location in order to prevent it from conflicting with 
other explicit PCI location assignments. For example when configuring 
the management network NIC to go to slot 0x05, libvirt would try to put 
the memballoon there as well and resulting in a fatal error.

lib/vagrant-libvirt/config.rb

@@ -119,6 +119,12 @@ module VagrantPlugins
       attr_accessor :tpm_path
       attr_accessor :tpm_version
 
+      # Configure the memballoon
+      attr_accessor :memballoon_enabled
+      attr_accessor :memballoon_model
+      attr_accessor :memballoon_pci_bus
+      attr_accessor :memballoon_pci_slot
+
       # Sets the max number of NICs that can be created
       # Default set to 8. Don't change the default unless you know
       # what are doing
@@ -248,6 +254,11 @@ module VagrantPlugins
         @tpm_path          = UNSET_VALUE
         @tpm_version       = UNSET_VALUE
 
+        @memballoon_enabled = UNSET_VALUE
+        @memballoon_model   = UNSET_VALUE
+        @memballoon_pci_bus = UNSET_VALUE
+        @memballoon_pci_slot = UNSET_VALUE
+
         @nic_adapter_count = UNSET_VALUE
 
         # Boot order
@@ -784,6 +795,10 @@ module VagrantPlugins
         @tpm_type = 'passthrough' if @tpm_type == UNSET_VALUE
         @tpm_path = nil if @tpm_path == UNSET_VALUE
         @tpm_version = nil if @tpm_version == UNSET_VALUE
+        @memballoon_enabled = nil if @memballoon_enabled == UNSET_VALUE
+        @memballoon_model = 'virtio' if @memballoon_model == UNSET_VALUE
+        @memballoon_pci_bus = '0x00' if @memballoon_pci_bus == UNSET_VALUE
+        @memballoon_pci_slot = '0x0f' if @memballoon_pci_slot == UNSET_VALUE
         @nic_adapter_count = 8 if @nic_adapter_count == UNSET_VALUE
         @emulator_path = nil if @emulator_path == UNSET_VALUE
 

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

@@ -271,6 +271,15 @@
     <%# USB Controller -%>
     <controller type='usb' model='<%= @usbctl_dev[:model] %>' <%= "ports=\"#{@usbctl_dev[:ports]}\" " if @usbctl_dev[:ports] %>/>
     <% end %>
+    <% unless @memballoon_enabled.nil? %>
+    <% if @memballoon_enabled %>
+    <memballoon model='<%= @memballoon_model %>'>
+      <address type='pci' domain='0x0000' bus='<%= @memballoon_pci_bus %>' slot='<%= @memballoon_pci_slot %>' function='0x0'/>
+    </memballoon>
+    <% else %>
+    <memballoon model='none'/>
+    <% end %>
+    <% end %>
   </devices>
 
   <% if not @qemu_args.empty? or not @qemu_env.empty? %>