vm/dispvm: place all volumes in the same pool as DispVM's template

Make all volume's pool controlled by DisposableVM Template. This
specifically makes DispVM's volatile volume to be placed directly in the
same pool as its template.

Fixes QubesOS/qubes-issues#5933

qubes/tests/vm/dispvm.py

@@ -168,3 +168,28 @@ class TC_00_DispVM(qubes.tests.QubesTestCase):
                 self.app.add_new_vm(qubes.vm.dispvm.DispVM,
                     name='test-dispvm', template=self.appvm)
             self.assertFalse(mock_domains.get_new_unused_dispid.called)
+
+    @mock.patch('os.symlink')
+    @mock.patch('os.makedirs')
+    def test_020_copy_storage_pool(self, mock_makedirs, mock_symlink):
+        self.app.pools['alternative'] = qubes.tests.vm.appvm.TestPool(name='alternative')
+        self.appvm.template_for_dispvms = True
+        self.loop.run_until_complete(self.template.create_on_disk())
+        self.loop.run_until_complete(self.appvm.create_on_disk(pool='alternative'))
+        orig_getitem = self.app.domains.__getitem__
+        with mock.patch.object(self.app, 'domains', wraps=self.app.domains) \
+                as mock_domains:
+            mock_domains.configure_mock(**{
+                'get_new_unused_dispid': mock.Mock(return_value=42),
+                '__getitem__.side_effect': orig_getitem
+            })
+            dispvm = self.app.add_new_vm(qubes.vm.dispvm.DispVM,
+                name='test-dispvm', template=self.appvm)
+            self.loop.run_until_complete(dispvm.create_on_disk())
+        self.assertEqual(dispvm.template, self.appvm)
+        self.assertEqual(dispvm.volumes['private'].pool,
+                         self.appvm.volumes['private'].pool)
+        self.assertEqual(dispvm.volumes['root'].pool,
+                         self.appvm.volumes['root'].pool)
+        self.assertEqual(dispvm.volumes['volatile'].pool,
+                         self.appvm.volumes['volatile'].pool)

qubes/vm/dispvm.py

@@ -109,6 +109,12 @@ class DispVM(qubes.vm.qubesvm.QubesVM):
                     self.volume_config[name] = config.copy()
                     if 'vid' in self.volume_config[name]:
                         del self.volume_config[name]['vid']
+                # copy pool setting from base AppVM; root and private would be
+                # in the same pool anyway (because of snap_on_start),
+                # but not volatile, which could be surprising
+                elif 'pool' not in self.volume_config[name] \
+                        and 'pool' in config:
+                    self.volume_config[name]['pool'] = config['pool']
 
         super(DispVM, self).__init__(app, xml, *args, **kwargs)