From e11f94b496f334984f04d1349cd23db605d1100f Mon Sep 17 00:00:00 2001
From: Demi Marie Obenour <athena@invisiblethingslab.com>
Date: Fri, 20 Nov 2020 01:35:13 -0500
Subject: [PATCH] Implement changing the template of a DispVM

---
 qubes/vm/dispvm.py          | 33 ++++++++++++++++++++++++++-------
 qubes/vm/mix/dvmtemplate.py | 10 ++++------
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/qubes/vm/dispvm.py b/qubes/vm/dispvm.py
index cd64ffff..6e089f48 100644
--- a/qubes/vm/dispvm.py
+++ b/qubes/vm/dispvm.py
@@ -145,14 +145,33 @@ class DispVM(qubes.vm.qubesvm.QubesVM):
         '''  # pylint: disable=unused-argument
         assert self.template
 
-    @qubes.events.handler('property-pre-set:template',
-        'property-pre-reset:template')
-    def on_property_pre_set_template(self, event, name, newvalue=None,
+    @qubes.events.handler('property-pre-reset:template')
+    def on_property_pre_reset_template(self, event, name, oldvalue=None):
+        '''Forbid deleting template of running VM
+        '''  # pylint: disable=unused-argument,no-self-use
+        raise qubes.exc.QubesValueError('Cannot unset template')
+
+    @qubes.events.handler('property-pre-set:template')
+    def on_property_pre_set_template(self, event, name, newvalue,
             oldvalue=None):
-        ''' Disposable VM cannot have template changed '''
-        # pylint: disable=unused-argument
-        raise qubes.exc.QubesValueError(self,
-            'Cannot change template of Disposable VM')
+        '''Forbid changing template of running VM
+        '''  # pylint: disable=unused-argument
+        if not self.is_halted():
+            raise qubes.exc.QubesVMNotHaltedError(self,
+                'Cannot change template while qube is running')
+
+    @qubes.events.handler('property-set:template')
+    def on_property_set_template(self, event, name, newvalue, oldvalue=None):
+        ''' Adjust root (and possibly other snap_on_start=True) volume
+        on template change.
+        '''  # pylint: disable=unused-argument
+
+        for volume_name, conf in self.default_volume_config.items():
+            if conf.get('snap_on_start', False) and \
+                    conf.get('source', None) is None:
+                config = conf.copy()
+                self.volume_config[volume_name] = config
+                self.storage.init_volume(volume_name, config)
 
     @qubes.events.handler('domain-shutdown')
     @asyncio.coroutine
diff --git a/qubes/vm/mix/dvmtemplate.py b/qubes/vm/mix/dvmtemplate.py
index ffff5e54..07b9103b 100644
--- a/qubes/vm/mix/dvmtemplate.py
+++ b/qubes/vm/mix/dvmtemplate.py
@@ -45,14 +45,12 @@ class DVMTemplateMixin(qubes.events.Emitter):
         self.__on_pre_set_dvmtemplate(
             event, name, False, oldvalue)
 
-    @qubes.events.handler('property-pre-set:template')
-    def __on_property_pre_set_template(self, event, name, newvalue,
+    @qubes.events.handler('property-set:template')
+    def __on_property_set_template(self, event, name, newvalue,
             oldvalue=None):
         # pylint: disable=unused-argument
-        if any(self.dispvms):
-            raise qubes.exc.QubesVMInUseError(self,
-                'Cannot change template '
-                'while there are DispVMs based on this qube')
+        for vm in self.dispvms:
+            vm.on_property_set_template(event, name, newvalue, oldvalue)
 
     @property
     def dispvms(self):