libvirt: add support for configuring hyperv enlightenments in XML

Extend the guest XML config classes to cope with the following
hyperv enlightenments:

   <features>
     <hyperv>
       <relaxed state='on'/>
       <vapic state='on'/>
       <spinlocks state='on' retries='4095'/>
     </hyperv>
   <features/>

Related-bug: #1400315
Change-Id: Ieff2ae44bf90e09152a56859709707ccdf83cbc9

nova/tests/unit/virt/libvirt/test_config.py

@@ -1269,6 +1269,35 @@ class LibvirtConfigGuestInterfaceTest(LibvirtConfigBaseTest):
             </interface>""")
 
 
+class LibvirtConfigGuestFeatureTest(LibvirtConfigBaseTest):
+
+    def test_feature_hyperv_relaxed(self):
+
+        obj = config.LibvirtConfigGuestFeatureHyperV()
+        obj.relaxed = True
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+          <hyperv>
+            <relaxed state="on"/>
+          </hyperv>""")
+
+    def test_feature_hyperv_all(self):
+
+        obj = config.LibvirtConfigGuestFeatureHyperV()
+        obj.relaxed = True
+        obj.vapic = True
+        obj.spinlocks = True
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+          <hyperv>
+            <relaxed state="on"/>
+            <vapic state="on"/>
+            <spinlocks state="on" retries="4095"/>
+          </hyperv>""")
+
+
 class LibvirtConfigGuestTest(LibvirtConfigBaseTest):
 
     def test_config_lxc(self):

nova/virt/libvirt/config.py

@@ -1733,6 +1733,34 @@ class LibvirtConfigGuestFeaturePAE(LibvirtConfigGuestFeature):
                                                            **kwargs)
 
 
+class LibvirtConfigGuestFeatureHyperV(LibvirtConfigGuestFeature):
+
+    # QEMU requires at least this value to be set
+    MIN_SPINLOCK_RETRIES = 4095
+
+    def __init__(self, **kwargs):
+        super(LibvirtConfigGuestFeatureHyperV, self).__init__("hyperv",
+                                                              **kwargs)
+
+        self.relaxed = False
+        self.vapic = False
+        self.spinlocks = False
+        self.spinlock_retries = self.MIN_SPINLOCK_RETRIES
+
+    def format_dom(self):
+        root = super(LibvirtConfigGuestFeatureHyperV, self).format_dom()
+
+        if self.relaxed:
+            root.append(etree.Element("relaxed", state="on"))
+        if self.vapic:
+            root.append(etree.Element("vapic", state="on"))
+        if self.spinlocks:
+            root.append(etree.Element("spinlocks", state="on",
+                                      retries=str(self.spinlock_retries)))
+
+        return root
+
+
 class LibvirtConfigGuest(LibvirtConfigObject):
 
     def __init__(self, **kwargs):