schema/v2: make mount source and target optional

The previous commit gave the individual mounts more control over the
source and target properties. Do not require them at the global
schema but hand the control if they are optional over to the modules.

osbuild/formats/v2.py

@@ -274,14 +274,16 @@ def load_mount(description: Dict, index: Index, stage: Stage):
     if name in stage.mounts:
         raise ValueError(f"Duplicated mount '{name}'")
 
-    source = description["source"]
-    target = description["target"]
+    source = description.get("source")
+    target = description.get("target")
 
     options = description.get("options", {})
 
-    device = stage.devices.get(source)
-    if not device:
-        raise ValueError(f"Unknown device '{source}' for mount '{name}'")
+    device = None
+    if source:
+        device = stage.devices.get(source)
+        if not device:
+            raise ValueError(f"Unknown device '{source}' for mount '{name}'")
 
     stage.add_mount(name, info, device, target, options)
 

osbuild/mounts.py

@@ -35,8 +35,10 @@ class Mount:
     def calc_id(self):
         m = hashlib.sha256()
         m.update(json.dumps(self.info.name, sort_keys=True).encode())
-        m.update(json.dumps(self.device.id, sort_keys=True).encode())
-        m.update(json.dumps(self.target, sort_keys=True).encode())
+        if self.device:
+            m.update(json.dumps(self.device.id, sort_keys=True).encode())
+        if self.target:
+            m.update(json.dumps(self.target, sort_keys=True).encode())
         m.update(json.dumps(self.options, sort_keys=True).encode())
         return m.hexdigest()
 

schemas/osbuild2.json

@@ -71,7 +71,7 @@
     "mount": {
       "title": "Mount point for a stage",
       "additionalProperties": false,
-      "required": ["name", "type", "source", "target"],
+      "required": ["name", "type"],
       "properties": {
         "name": { "type": "string" },
         "type": { "type": "string" },