storage: improve/fix handling extra volumes

Just calling pool.init_volume isn't enough - a lot of code depends on
additional data loaded into vm.storage object. Provide a convenient
wrapper for this.

At the same time, fix loading extra volumes from qubes.xml - don't fail
on volume not mentioned in initial vm.volume_config.

QubesOS/qubes-issues#2256

qubes/storage/__init__.py

@@ -194,14 +194,23 @@ def __init__(self, vm):
 
         if hasattr(vm, 'volume_config'):
             for name, conf in self.vm.volume_config.items():
-                assert 'pool' in conf, "Pool missing in volume_config" % str(
-                    conf)
                 if 'volume_type' in conf:
                     conf = self._migrate_config(conf)
 
-                pool = self.vm.app.get_pool(conf['pool'])
-                self.vm.volumes[name] = pool.init_volume(self.vm, conf)
-                self.pools[name] = pool
+                self.init_volume(name, conf)
+
+    def init_volume(self, name, volume_config):
+        ''' Initialize Volume instance attached to this domain '''
+        assert 'pool' in volume_config, "Pool missing in volume_config" % str(
+            volume_config)
+
+        if 'name' not in volume_config:
+            volume_config['name'] = name
+        pool = self.vm.app.get_pool(volume_config['pool'])
+        volume = pool.init_volume(self.vm, volume_config)
+        self.vm.volumes[name] = volume
+        self.pools[name] = pool
+        return volume
 
     def _migrate_config(self, conf):
         ''' Migrates from the old config style to new

qubes/vm/qubesvm.py

@@ -427,14 +427,19 @@ def __init__(self, app, xml, volume_config=None, **kwargs):
                     for key, value in node.items():
                         # pylint: disable=no-member
                         if value == 'True':
-                            self.volume_config[name][key] = True
-                        else:
+                            value = True
+                        try:
                             self.volume_config[name][key] = value
+                        except KeyError:
+                            self.volume_config[name] = {key: value}
 
             for name, conf in volume_config.items():
                 for key, value in conf.items():
                     # pylint: disable=no-member
-                    self.volume_config[name][key] = value
+                    try:
+                        self.volume_config[name][key] = value
+                    except KeyError:
+                        self.volume_config[name] = {key: value}
 
         elif volume_config:
             raise TypeError(