storage: make volume snap_on_start/save_on_stop explicit

Always define those properties, always include them in volume config.
Also simplify overriding pool based on volume type defined by those:
override pool unless snap_on_start=True.

QubesOS/qubes-issues#2256

qubes/storage/__init__.py

@@ -262,29 +262,21 @@ def size(self, size):
     @property
     def config(self):
         ''' return config data for serialization to qubes.xml '''
-        result = {'name': self.name, 'pool': str(self.pool), 'vid': self.vid, }
-
-        if self.internal:
-            result['internal'] = self.internal
-
-        if self.removable:
-            result['removable'] = self.removable
-
-        if self.revisions_to_keep:
-            result['revisions_to_keep'] = self.revisions_to_keep
-
-        if self.rw:
-            result['rw'] = self.rw
-
-        if self.save_on_stop:
-            result['save_on_stop'] = self.save_on_stop
+        result = {
+            'name': self.name,
+            'pool': str(self.pool),
+            'vid': self.vid,
+            'internal': self.internal,
+            'removable': self.removable,
+            'revisions_to_keep': self.revisions_to_keep,
+            'rw': self.rw,
+            'save_on_stop': self.save_on_stop,
+            'snap_on_start': self.snap_on_start,
+        }
 
         if self.size:
             result['size'] = self.size
 
-        if self.snap_on_start:
-            result['snap_on_start'] = self.snap_on_start
-
         if self.source:
             result['source'] = str(self.source)
 

qubes/vm/appvm.py

@@ -63,13 +63,17 @@ class AppVM(qubes.vm.qubesvm.QubesVM):
             'volatile': {
                 'name': 'volatile',
                 'pool': 'default',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'size': defaults['root_img_size'],
                 'internal': True,
                 'rw': True,
             },
             'kernel': {
                 'name': 'kernel',
                 'pool': 'linux-kernel',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'rw': False,
                 'internal': True
             }

qubes/vm/dispvm.py

@@ -61,13 +61,17 @@ def __init__(self, *args, **kwargs):
                 'name': 'volatile',
                 'pool': 'default',
                 'internal': True,
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'rw': True,
                 'size': qubes.config.defaults['root_img_size'] +
                         qubes.config.defaults['private_img_size'],
             },
             'kernel': {
                 'name': 'kernel',
                 'pool': 'linux-kernel',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'rw': False,
                 'internal': True
             }

qubes/vm/qubesvm.py

@@ -1824,20 +1824,17 @@ def _clean_volume_config(config):
 
 def _patch_pool_config(config, pool=None, pools=None):
     assert pool is not None or pools is not None
-    is_saveable = 'save_on_stop' in config and config['save_on_stop']
-    is_resetable = not ('snap_on_start' in config and  # volatile
-                        config['snap_on_start'] and not is_saveable)
-
-    is_exportable = is_saveable or is_resetable
+    is_snapshot = config['snap_on_start']
+    is_rw = config['rw']
 
     name = config['name']
 
-    if pool and is_exportable and config['pool'] == 'default':
+    if pool and not is_snapshot and is_rw:
         config['pool'] = str(pool)
-    elif pool and not is_exportable:
+    elif pool:
         pass
     elif pools and name in pools.keys():
-        if is_exportable:
+        if not is_snapshot:
             config['pool'] = str(pools[name])
         else:
             msg = "Can't clone a snapshot volume {!s} to pool {!s} " \

qubes/vm/standalonevm.py

@@ -51,13 +51,17 @@ def __init__(self, *args, **kwargs):
             'volatile': {
                 'name': 'volatile',
                 'pool': 'default',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'internal': True,
                 'rw': True,
                 'size': qubes.config.defaults['root_img_size'],
             },
             'kernel': {
                 'name': 'kernel',
                 'pool': 'linux-kernel',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'rw': False,
                 'internal': True
             }

qubes/vm/templatevm.py

@@ -88,12 +88,16 @@ def __init__(self, *args, **kwargs):
                 'name': 'volatile',
                 'pool': 'default',
                 'size': defaults['root_img_size'],
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'internal': True,
                 'rw': True,
             },
             'kernel': {
                 'name': 'kernel',
                 'pool': 'linux-kernel',
+                'snap_on_start': False,
+                'save_on_stop': False,
                 'internal': True,
                 'rw': False
             }