api/admin: include 'revisions_to_keep' and 'is_outdated' in volume info

Since Volume.is_outdated() is a method, not a property, add a function
for handling serialization. And at the same time, fix None serialization
(applicable to 'source' property).

QubesOS/qubes-issues#3256

qubes/api/admin.py

@@ -336,9 +336,16 @@ class QubesAdminAPI(qubes.api.AbstractQubesAPI):
         # properties defined in API
         volume_properties = [
             'pool', 'vid', 'size', 'usage', 'rw', 'source',
-            'save_on_stop', 'snap_on_start']
-        return ''.join('{}={}\n'.format(key, getattr(volume, key)) for key in
-            volume_properties)
+            'save_on_stop', 'snap_on_start', 'revisions_to_keep', 'is_outdated']
+
+        def _serialize(value):
+            if callable(value):
+                value = value()
+            if value is None:
+                value = ''
+            return str(value)
+        return ''.join('{}={}\n'.format(key, _serialize(getattr(volume, key)))
+            for key in volume_properties)
 
     @qubes.api.method('admin.vm.volume.ListSnapshots', no_payload=True,
         scope='local', read=True)

qubes/tests/api_admin.py

@@ -40,7 +40,7 @@ import qubes.storage
 # properties defined in API
 volume_properties = [
     'pool', 'vid', 'size', 'usage', 'rw', 'source',
-    'save_on_stop', 'snap_on_start']
+    'save_on_stop', 'snap_on_start', 'revisions_to_keep', 'is_outdated']
 
 
 class AdminAPITestCase(qubes.tests.QubesTestCase):