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

(cherry picked from commit 8b76045)

qubes/tests/vm/dispvm.py

@@ -168,3 +168,28 @@ def test_011_create_direct_reject(self):
                 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 @@ def __init__(self, app, xml, *args, **kwargs):
                     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)