From a457b62728e57d59267b647414f1e233527bfafd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Thu, 21 Nov 2013 03:39:08 +0100
Subject: [PATCH] core: more flexible mechanism for template compatibility
 check

Using class method allow the users (Qubes Manager at least) to check
for compatibility without having any particular VM instance - useful
while creating the VM.
---
 core-modules/000QubesVm.py | 17 ++++++++++++-----
 core-modules/01QubesHVm.py | 14 +++++---------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/core-modules/000QubesVm.py b/core-modules/000QubesVm.py
index 5257b50c..36d37c3e 100644
--- a/core-modules/000QubesVm.py
+++ b/core-modules/000QubesVm.py
@@ -459,17 +459,24 @@ class QubesVm(object):
             raise QubesException("Failed to set autostart for VM via systemctl")
         self._autostart = bool(value)
 
+    @classmethod
+    def is_template_compatible(cls, template):
+        """Check if given VM can be a template for this VM"""
+        # FIXME: check if the value is instance of QubesTemplateVM, not the VM
+        # type. The problem is while this file is loaded, QubesTemplateVM is
+        # not defined yet.
+        if template and (not template.is_template() or template.type != "TemplateVM"):
+            return False
+        return True
+
     @property
     def template(self):
         return self._template
 
     @template.setter
     def template(self, value):
-        # FIXME: check if the value is instance of QubesTemplateVM, not the VM
-        # type. The problem is while this file is loaded, QubesTemplateVM is
-        # not defined yet.
-        if value and (not value.is_template() or value.type != "TemplateVM"):
-            raise QubesException("Only PV template can be a template for the PV VM")
+        if value and not self.is_template_compatible(value):
+            raise QubesException("Incompatible template type %s with VM of type %s" % (value.type, self.type))
         self._template = value
 
     def is_template(self):
diff --git a/core-modules/01QubesHVm.py b/core-modules/01QubesHVm.py
index 0e657834..2fa7d5a9 100644
--- a/core-modules/01QubesHVm.py
+++ b/core-modules/01QubesHVm.py
@@ -101,15 +101,11 @@ class QubesHVm(QubesVm):
         # Any non-template based HVM can be a template itself
         return self.template is None
 
-    @property
-    def template(self):
-        return self._template
-
-    @template.setter
-    def template(self, value):
-        if value and (not value.is_template() or value.type != "HVM"):
-            raise QubesException("Only HVM can be a template for the HVM")
-        self._template = value
+    @classmethod
+    def is_template_compatible(cls, template):
+        if template and (not template.is_template() or template.type != "HVM"):
+            return False
+        return True
 
     def get_clone_attrs(self):
         attrs = super(QubesHVm, self).get_clone_attrs()