libvirt: deprecate use_usb_tablet in favor of pointer_model

A new global option to handle input devices has
been introduced. The specifc option use_usb_tablet in the
group libvirt has been depecreated for Newton and should be
removed for O*

Related-To: blueprint virt-configure-usb-tablet-from-image
Change-Id: I51186530a94d86c8ed14783c7d42d0a3bd601f59

nova/conf/virt.py

@@ -324,6 +324,31 @@
     help='Unused unresized base images younger than this will not '
     'be removed')
 
+pointer_model = cfg.StrOpt(
+    'pointer_model',
+    default=None, choices=[None, 'usbtablet'],
+    help="""Generic property to specify the pointer type.
+
+Input devices allow interaction with a graphical framebuffer. For
+example to provide a graphic tablet for absolute cursor movement.
+
+Possible values:
+
+* None: Uses relative movement. Mouse connected by PS2
+* usbtablet: Uses absolute movement. Tablet connect by USB
+
+Services which consume this:
+
+* nova-compute
+
+Interdependencies to other options:
+
+* usbtablet must be configured with VNC enabled or SPICE enabled and SPICE
+  agent disabled. When used with libvirt the instance mode should be
+  configured as HVM.
+ """)
+
+
 ALL_OPTS = [vcpu_pin_set,
             compute_driver,
             default_ephemeral_format,
@@ -341,7 +366,8 @@
             image_cache_manager_interval,
             image_cache_subdirectory_name,
             remove_unused_base_images,
-            remove_unused_original_minimum_age_seconds]
+            remove_unused_original_minimum_age_seconds,
+            pointer_model]
 
 
 def register_opts(conf):

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

@@ -3834,7 +3834,7 @@ def _test_get_guest_usb_tablet(self, vnc_enabled, spice_enabled, os_type,
         self.flags(enabled=spice_enabled,
                    agent_enabled=agent_enabled, group='spice')
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
-        return drvr._get_guest_usb_tablet(os_type)
+        return drvr._get_guest_pointer_model(os_type)
 
     def test_get_guest_usb_tablet_wipe(self):
         self.flags(use_usb_tablet=True, group='libvirt')
@@ -3858,6 +3858,24 @@ def test_get_guest_usb_tablet_wipe(self):
             False, True, vm_mode.HVM, True)
         self.assertIsNone(tablet)
 
+    def test_get_guest_no_pointer_model_usb_tablet_set(self):
+        self.flags(use_usb_tablet=True, group='libvirt')
+
+        tablet = self._test_get_guest_usb_tablet(True, True, vm_mode.HVM)
+        self.assertIsNotNone(tablet)
+
+    def test_get_guest_no_pointer_model_usb_tablet_not_set(self):
+        self.flags(use_usb_tablet=False, group='libvirt')
+
+        tablet = self._test_get_guest_usb_tablet(True, True, vm_mode.HVM)
+        self.assertIsNone(tablet)
+
+    def test_get_guest_pointer_model_usb_tablet(self):
+        self.flags(use_usb_tablet=False, group='libvirt')
+        self.flags(pointer_model='usbtablet')
+        tablet = self._test_get_guest_usb_tablet(True, True, vm_mode.HVM)
+        self.assertIsNotNone(tablet)
+
     def _test_get_guest_config_with_watchdog_action_flavor(self,
             hw_watchdog_action="hw:watchdog_action"):
         self.flags(virt_type='kvm', group='libvirt')

nova/virt/libvirt/driver.py

@@ -156,7 +156,9 @@
                      '0 => not partitioned, >0 => partition number'),
     cfg.BoolOpt('use_usb_tablet',
                 default=True,
-                help='Sync virtual and real mouse cursors in Windows VMs'),
+                deprecated_for_removal=True,
+                help='(Deprecated, please see pointer_model) Sync virtual and '
+                     'real mouse cursors in Windows VMs'),
     cfg.StrOpt('live_migration_inbound_addr',
                help='Live migration target ip or hostname '
                     '(if this option is set to None, which is the default, '
@@ -4608,9 +4610,9 @@ def _get_guest_config(self, instance, network_info, image_meta,
             consolepty.type = "pty"
             guest.add_device(consolepty)
 
-        tablet = self._get_guest_usb_tablet(guest.os_type)
-        if tablet:
-            guest.add_device(tablet)
+        pointer = self._get_guest_pointer_model(guest.os_type)
+        if pointer:
+            guest.add_device(pointer)
 
         if (CONF.spice.enabled and CONF.spice.agent_enabled and
                 virt_type not in ('lxc', 'uml', 'xen')):
@@ -4691,26 +4693,50 @@ def _get_guest_config(self, instance, network_info, image_meta,
 
         return guest
 
-    def _get_guest_usb_tablet(self, os_type):
-        # We want a tablet if VNC is enabled, or SPICE is enabled and
-        # the SPICE agent is disabled. If the SPICE agent is enabled
-        # it provides a paravirt mouse which drastically reduces
-        # overhead (by eliminating USB polling).
-        #
-        # NB: this implies that if both SPICE + VNC are enabled
-        # at the same time, we'll get the tablet whether the
-        # SPICE agent is used or not.
-        need_usb_tablet = False
-        if CONF.vnc.enabled:
-            need_usb_tablet = CONF.libvirt.use_usb_tablet
-        elif CONF.spice.enabled and not CONF.spice.agent_enabled:
-            need_usb_tablet = CONF.libvirt.use_usb_tablet
+    def _get_guest_pointer_model(self, os_type):
+        pointer_model = CONF.pointer_model
+        if pointer_model is None and CONF.libvirt.use_usb_tablet:
+            # TODO(sahid): We set pointer_model to keep compatibility
+            # until the next release O*. It means operators can continue
+            # to use the depecrated option "use_usb_tablet" or set a
+            # specific device to use
+            pointer_model = "usbtablet"
+            LOG.warning(_LW('The option "use_usb_tablet" has been '
+                            'deprecated for Newton in favor of the more '
+                            'generic "pointer_model". Please update '
+                            'nova.conf to address this change.'))
+
+        if pointer_model == "usbtablet":
+            # We want a tablet if VNC is enabled, or SPICE is enabled and
+            # the SPICE agent is disabled. If the SPICE agent is enabled
+            # it provides a paravirt mouse which drastically reduces
+            # overhead (by eliminating USB polling).
+            if CONF.vnc.enabled or (
+                    CONF.spice.enabled and not CONF.spice.agent_enabled):
+                return self._get_guest_usb_tablet(os_type)
+            else:
+                # For backward compatibility We don't want to break
+                # process of booting an instance if host is configured
+                # to use USB tablet without VNC or SPICE and SPICE
+                # agent disable.
+                LOG.warning(_LW('USB tablet requested for guests by host '
+                                'configuration. In order to accept this '
+                                'request VNC should be enabled or SPICE '
+                                'and SPICE agent disabled on host.'))
 
+    def _get_guest_usb_tablet(self, os_type):
         tablet = None
-        if need_usb_tablet and os_type == vm_mode.HVM:
+        if os_type == vm_mode.HVM:
             tablet = vconfig.LibvirtConfigGuestInput()
             tablet.type = "tablet"
             tablet.bus = "usb"
+        else:
+            # For backward compatibility We don't want to break
+            # process of booting an instance if virtual machine mode
+            # is not configured as HVM.
+            LOG.warning(_LW('USB tablet requested for guests by host '
+                            'configuration. In order to accept this request '
+                            'the machine mode should be configured as HVM.'))
         return tablet
 
     def _get_guest_xml(self, context, instance, network_info, disk_info,

releasenotes/notes/pointer-model-b4a1828c43e8d523.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - The pointer_model configuration option was added to specify
+    different pointer models for input devices. This replaces
+    the now deprecated use_usb_tablet option.
+deprecations:
+  - Nova option 'use_usb_tablet' will be deprecated in favor of
+    the global 'pointer_model'.