Add support for VMs with no box

Vagrant already supports VMs without boxes with Docker.
We leverage this in libvirt as well. The use case for this is to PXE
oot a vagrant VM that is then installed over the network then
installed over the network; a different use case would be to test PXE
booted clients that do not use a hard drive whatsoever.

README.md

@@ -22,6 +22,7 @@ welcome and can help a lot :-)
 * Snapshots via [sahara](https://github.com/jedi4ever/sahara).
 * Package caching via [vagrant-cachier](http://fgrehm.viewdocs.io/vagrant-cachier/).
 * Use boxes from other Vagrant providers via [vagrant-mutate](https://github.com/sciurus/vagrant-mutate).
+* Support VMs with no box for PXE boot purposes
 
 ## Future work
 
@@ -425,6 +426,26 @@ Vagrant.configure("2") do |config|
 end
 ```
 
+## No box and PXE boot
+
+There is support for PXE booting VMs with no disks as well as PXE booting VMs with blank disks. There are some limitations:
+
+* No provisioning scripts are ran
+* No network configuration is being applied to the VM
+* No SSH connection can be made
+* ```vagrant halt``` will only work cleanly if the VM handles ACPI shutdown signals 
+
+In short, VMs without a box can be created, halted and destroyed but all other functionality cannot be used.
+
+An example for a PXE booted VM with no disks whatsoever:
+
+Vagrant.configure("2") do |config|
+  config.vm.define :pxeclient do |pxeclient|
+    pxeclient.vm.provider :libvirt do |domain|
+      domain.boot 'network'
+    end
+  end
+
 ## SSH Access To VM
 
 vagrant-libvirt supports vagrant's [standard ssh settings](https://docs.vagrantup.com/v2/vagrantfile/ssh_settings.html).

lib/vagrant-libvirt/action.rb

@@ -23,6 +23,12 @@ module VagrantPlugins
             # Create VM if not yet created.
             if !env[:result]
               b2.use SetNameOfDomain
+              if !env[:machine].box
+                b2.use CreateDomain
+                b2.use CreateNetworks
+                b2.use CreateNetworkInterfaces
+                b2.use StartDomain
+              else
                 b2.use HandleStoragePool
                 b2.use HandleBox
                 b2.use HandleBoxImage
@@ -44,6 +50,7 @@ module VagrantPlugins
                 b2.use ForwardPorts
                 b2.use SetHostname
                 # b2.use SyncFolders
+              end
             else
               b2.use action_start
             end
@@ -68,6 +75,11 @@ module VagrantPlugins
                 next
               end
 
+              if !env[:machine].box
+                # With no box, we just care about network creation and starting it
+                b3.use CreateNetworks
+                b3.use StartDomain
+              else
                 # VM is not running or suspended.
 
                 b3.use Provision
@@ -93,6 +105,7 @@ module VagrantPlugins
             end
           end
         end
+      end
 
       # This is the action that is primarily responsible for halting the
       # virtual machine.
@@ -154,7 +167,9 @@ module VagrantPlugins
             if !env[:result]
               # Try to remove stale volumes anyway
               b2.use SetNameOfDomain
+	      if env[:machine].box
                 b2.use RemoveStaleVolume
+              end
               if !env[:result]
                 b2.use MessageNotCreated
               end

lib/vagrant-libvirt/action/create_domain.rb

@@ -72,18 +72,29 @@ module VagrantPlugins
 
           @os_type = 'hvm'
 
-          # Get path to domain image from the storage pool selected.
+          # Get path to domain image from the storage pool selected if we have a box.
+          if env[:machine].box
             actual_volumes = 
               env[:machine].provider.driver.connection.volumes.all.select do |x|
                 x.pool_name == @storage_pool_name
               end
             domain_volume = ProviderLibvirt::Util::Collection.find_matching(
-            actual_volumes, "#{@name}.img")
+              actual_volumes,"#{@name}.img")
             raise Errors::DomainVolumeExists if domain_volume.nil?
             @domain_volume_path = domain_volume.path
+          end
 
+          # If we have a box, take the path from the domain volume and set our storage_prefix.
+          # If not, we dump the storage pool xml to get its defined path.
           # the default storage prefix is typically: /var/lib/libvirt/images/
+          if env[:machine].box
             storage_prefix = File.dirname(@domain_volume_path) + '/'        # steal
+          else
+            storage_pool = env[:machine].provider.driver.connection.client.lookup_storage_pool_by_name(@storage_pool_name)
+            raise Errors::NoStoragePool if storage_pool.nil?
+            xml = Nokogiri::XML(storage_pool.xml_desc)
+            storage_prefix = xml.xpath("/pool/target/path").inner_text.to_s + '/'
+          end
 
           @disks.each do |disk|
             disk[:path] ||= _disk_name(@name, disk)
@@ -125,7 +136,9 @@ module VagrantPlugins
           env[:ui].info(" -- Cpus:              #{@cpus}")
           env[:ui].info(" -- Memory:            #{@memory_size / 1024}M")
           env[:ui].info(" -- Loader:            #{@loader}")
+          if env[:machine].box
             env[:ui].info(" -- Base box:          #{env[:machine].box.name}")
+          end
           env[:ui].info(" -- Storage pool:      #{@storage_pool_name}")
           env[:ui].info(" -- Image:             #{@domain_volume_path} (#{env[:box_virtual_size]}G)")
           env[:ui].info(" -- Volume Cache:      #{@domain_volume_cache}")

lib/vagrant-libvirt/action/create_network_interfaces.rb

@@ -125,6 +125,8 @@ module VagrantPlugins
           # Continue the middleware chain.
           @app.call(env)
 
+
+          if env[:machine].box
             # Configure interfaces that user requested. Machine should be up and
             # running now.
             networks_to_configure = []
@@ -163,6 +165,7 @@ module VagrantPlugins
             env[:machine].guest.capability(
               :configure_networks, networks_to_configure)
           end
+        end
 
         private
 

lib/vagrant-libvirt/plugin.rb

@@ -23,7 +23,7 @@ module VagrantPlugins
         Config
       end
 
-      provider('libvirt', parallel: true) do
+      provider('libvirt', parallel: true, box_optional: true) do
         require_relative 'provider'
         Provider
       end

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

@@ -49,12 +49,14 @@
   </features>
   <clock offset='utc'/>
   <devices>
+    <% if @domain_volume_path %>
     <disk type='file' device='disk'>
       <driver name='qemu' type='qcow2' cache='<%= @domain_volume_cache %>'/>
       <source file='<%= @domain_volume_path %>'/>
       <%# we need to ensure a unique target dev -%>
       <target dev='vda' bus='<%= @disk_bus %>'/>
     </disk>
+    <% end %>
 <%# additional disks -%>
 <% @disks.each do |d| -%>
     <disk type='file' device='disk'>