libvirt: add support for memory backing parameters

Add a libvirt config class for dealing with the XML elements
under the <memoryBacking> section of the guest schema.

Blueprint: virt-driver-large-pages
Change-Id: Icd89508671a8951bed480b901b2d12d44ebb7cab

nova/tests/virt/libvirt/test_config.py

@@ -1136,6 +1136,9 @@ class LibvirtConfigGuestTest(LibvirtConfigBaseTest):
         obj.cputune.quota = 50000
         obj.cputune.period = 25000
 
+        obj.membacking = config.LibvirtConfigGuestMemoryBacking()
+        obj.membacking.hugepages = True
+
         obj.name = "demo"
         obj.uuid = "b38a3f43-4be2-4046-897f-b67c2f5e0147"
         obj.os_type = "linux"
@@ -1162,6 +1165,9 @@ class LibvirtConfigGuestTest(LibvirtConfigBaseTest):
               <uuid>b38a3f43-4be2-4046-897f-b67c2f5e0147</uuid>
               <name>demo</name>
               <memory>104857600</memory>
+              <memoryBacking>
+                <hugepages/>
+              </memoryBacking>
               <vcpu cpuset="0-1,3-5">2</vcpu>
               <sysinfo type='smbios'>
                  <bios>
@@ -1785,6 +1791,28 @@ class LibvirtConfigGuestCPUTuneTest(LibvirtConfigBaseTest):
           </cputune>""")
 
 
+class LibvirtConfigGuestMemoryBackingTest(LibvirtConfigBaseTest):
+    def test_config_memory_backing_none(self):
+        obj = config.LibvirtConfigGuestMemoryBacking()
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, "<memoryBacking/>")
+
+    def test_config_memory_backing_all(self):
+        obj = config.LibvirtConfigGuestMemoryBacking()
+        obj.locked = True
+        obj.sharedpages = False
+        obj.hugepages = True
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+          <memoryBacking>
+            <hugepages/>
+            <nosharedpages/>
+            <locked/>
+          </memoryBacking>""")
+
+
 class LibvirtConfigGuestMetadataNovaTest(LibvirtConfigBaseTest):
 
     def test_config_metadata(self):

nova/virt/libvirt/config.py

@@ -1307,6 +1307,29 @@ class LibvirtConfigGuestCPUTune(LibvirtConfigObject):
         return root
 
 
+class LibvirtConfigGuestMemoryBacking(LibvirtConfigObject):
+
+    def __init__(self, **kwargs):
+        super(LibvirtConfigGuestMemoryBacking, self).__init__(
+            root_name="memoryBacking", **kwargs)
+
+        self.hugepages = False
+        self.sharedpages = True
+        self.locked = False
+
+    def format_dom(self):
+        root = super(LibvirtConfigGuestMemoryBacking, self).format_dom()
+
+        if self.hugepages:
+            root.append(etree.Element("hugepages"))
+        if not self.sharedpages:
+            root.append(etree.Element("nosharedpages"))
+        if self.locked:
+            root.append(etree.Element("locked"))
+
+        return root
+
+
 class LibvirtConfigGuest(LibvirtConfigObject):
 
     def __init__(self, **kwargs):
@@ -1317,6 +1340,7 @@ class LibvirtConfigGuest(LibvirtConfigObject):
         self.uuid = None
         self.name = None
         self.memory = 500 * units.Mi
+        self.membacking = None
         self.vcpus = 1
         self.cpuset = None
         self.cpu = None
@@ -1342,6 +1366,8 @@ class LibvirtConfigGuest(LibvirtConfigObject):
         root.append(self._text_node("uuid", self.uuid))
         root.append(self._text_node("name", self.name))
         root.append(self._text_node("memory", self.memory))
+        if self.membacking is not None:
+            root.append(self.membacking.format_dom())
         if self.cpuset is not None:
             vcpu = self._text_node("vcpu", self.vcpus)
             vcpu.set("cpuset", hardware.format_cpu_spec(self.cpuset))