Handle global disposable preload feature

For: QubesOS/qubes-issues#1512
For: QubesOS/qubes-desktop-linux-manager#262

Author: ben-grande

qubes/app.py

@@ -1732,9 +1732,12 @@ def on_property_set_default_netvm(
                     "property-reset:netvm", name="netvm", oldvalue=oldvalue
                 )
 
-    @qubes.events.handler("property-set:default_dispvm")
+    @qubes.events.handler(
+        "property-set:default_dispvm",
+        "property-reset:default_dispvm",
+    )
     def on_property_set_default_dispvm(
-        self, event, name, newvalue, oldvalue=None
+        self, event, name, newvalue=None, oldvalue=None
     ):
         # pylint: disable=unused-argument
         for vm in self.domains:
@@ -1749,6 +1752,33 @@ def on_property_set_default_dispvm(
                     oldvalue=oldvalue,
                 )
 
+        if not newvalue:
+            newvalue = self.default_dispvm
+        if newvalue == oldvalue:
+            return
+        old_appvm = None
+        appvm = None
+        if oldvalue:
+            old_appvm = self.domains[oldvalue]
+            old_appvm.preload_max_ignore_global = True
+        if newvalue:
+            appvm = self.domains[newvalue]
+            appvm.preload_max_ignore_global = False
+        if old_appvm and old_appvm.is_global_preload_distinct():
+            asyncio.ensure_future(
+                old_appvm.fire_event_async(
+                    "domain-preload-dispvm-start",
+                    reason="it was the default_dispvm",
+                )
+            )
+        if appvm and appvm.is_global_preload_distinct():
+            asyncio.ensure_future(
+                appvm.fire_event_async(
+                    "domain-preload-dispvm-start",
+                    reason="it became the default_dispvm",
+                )
+            )
+
     @qubes.events.handler("property-pre-set:default_kernel")
     # pylint: disable-next=invalid-name
     def on_property_pre_set_default_kernel(

qubes/tests/app.py

@@ -689,13 +689,6 @@ def test_101_property_migrate_label(self):
 
 
 class TC_90_Qubes(qubes.tests.QubesTestCase):
-    def tearDown(self):
-        try:
-            os.unlink("/tmp/qubestest.xml")
-        except:
-            pass
-        super().tearDown()
-
     def setUp(self):
         super(TC_90_Qubes, self).setUp()
         self.app = qubes.Qubes(
@@ -707,12 +700,43 @@ def setUp(self):
         self.template = self.app.add_new_vm(
             "TemplateVM", name="test-template", label="green"
         )
+        self.template.features["qrexec"] = True
+        self.template.features["supported-rpc.qubes.WaitForRunningSystem"] = (
+            True
+        )
+        self.appvm = self.app.add_new_vm(
+            "AppVM",
+            name="test-dvm",
+            template=self.template,
+            label="red",
+        )
+        self.appvm_alt = self.app.add_new_vm(
+            qubes.vm.appvm.AppVM,
+            name="test-alt-dvm",
+            template=self.template,
+            label="red",
+        )
+        for qube in [self.appvm, self.appvm_alt]:
+            qube.features["gui"] = False
+            qube.template_for_dispvms = True
+        self.app.save()
+        self.emitter = qubes.tests.TestEmitter()
+
+    def tearDown(self):
+        try:
+            os.unlink("/tmp/qubestest.xml")
+        except:
+            pass
+        del self.emitter
+        super().tearDown()
 
     def cleanup_qubes(self):
         self.app.close()
         del self.app
         try:
             del self.template
+            del self.appvm
+            del self.appvm_alt
         except AttributeError:
             pass
 
@@ -932,11 +956,7 @@ def test_116_remotevm_add_and_remove(self):
 
         assert remotevm1 in self.app.domains
         del self.app.domains["remote-vm1"]
-
-        self.assertCountEqual(
-            {d.name for d in self.app.domains},
-            {"dom0", "test-template", "test-vm", "remote-vm2"},
-        )
+        assert "remote-vm1" not in self.app.domains
 
     def test_117_remotevm_status(self):
         remotevm1 = self.app.add_new_vm(
@@ -1096,6 +1116,73 @@ def test_207_default_kernel(self):
                 existence.side_effect = [True, False]
                 self.app.default_kernel = "unittest_GNU_Hurd_1.0.0"
 
+    def test_300_preload_default_dispvm(self):
+        """Fire event for new setting from no previous one."""
+        self.appvm.features["preload-dispvm-max"] = "1"
+        with mock.patch.object(self.appvm, "fire_event_async") as mock_events:
+            self.app.default_dispvm = self.appvm
+            mock_events.assert_called_once()
+            self.assertEqual(
+                "domain-preload-dispvm-start", mock_events.call_args[0][0]
+            )
+
+    def test_301_preload_default_dispvm_change(self):
+        """Fire event for old and new setting."""
+        self.appvm.features["preload-dispvm-max"] = "1"
+        self.app.default_dispvm = self.appvm
+        self.appvm_alt.features["preload-dispvm-max"] = "1"
+        with mock.patch.object(
+            self.appvm, "fire_event_async"
+        ) as mock_old, mock.patch.object(
+            self.appvm_alt, "fire_event_async"
+        ) as mock_new:
+            self.app.default_dispvm = self.appvm_alt
+            mock_old.assert_called_once()
+            mock_new.assert_called_once()
+            self.assertEqual(
+                "domain-preload-dispvm-start", mock_new.call_args[0][0]
+            )
+            self.assertEqual(
+                "domain-preload-dispvm-start", mock_new.call_args[0][0]
+            )
+
+    def test_302_preload_default_dispvm_change_noop(self):
+        """If global feature has the same value as the new and old setting,
+        don't fire the event.
+        """
+        self.appvm.features["preload-dispvm-max"] = "1"
+        self.appvm_alt.features["preload-dispvm-max"] = "1"
+        self.app.domains["dom0"].features["preload-dispvm-max"] = "1"
+        self.app.default_dispvm = self.appvm
+        with mock.patch.object(
+            self.appvm, "fire_event_async"
+        ) as mock_old, mock.patch.object(
+            self.appvm_alt, "fire_event_async"
+        ) as mock_new:
+            self.app.default_dispvm = self.appvm_alt
+            mock_old.assert_not_called()
+            mock_new.assert_not_called()
+
+    def test_303_preload_default_dispvm_change_partial_noop(self):
+        """If global feature has the same value as the new or old setting,
+        don't fire the event.
+        """
+        self.appvm.features["preload-dispvm-max"] = "2"
+        self.appvm_alt.features["preload-dispvm-max"] = "1"
+        self.app.domains["dom0"].features["preload-dispvm-max"] = "2"
+        self.app.default_dispvm = self.appvm
+        with mock.patch.object(
+            self.appvm, "fire_event_async"
+        ) as mock_old, mock.patch.object(
+            self.appvm_alt, "fire_event_async"
+        ) as mock_new:
+            self.app.default_dispvm = self.appvm_alt
+            mock_old.assert_not_called()
+            mock_new.assert_called_once()
+            self.assertEqual(
+                "domain-preload-dispvm-start", mock_new.call_args[0][0]
+            )
+
     @qubes.tests.skipUnlessGit
     def test_900_example_xml_in_doc(self):
         self.assertXMLIsValid(