Reject incomplete backing ancestry and allow empty optical drives

hydra/installer.py

@@ -97,8 +97,13 @@ class Topology:
             size, identity = node.get('size'), node.get('maj:min')
             if not isinstance(mounts, list) or any(m is not None and not isinstance(m, str) for m in mounts):
                 raise InstallError('Malformed lsblk mountpoints')
-            if isinstance(size, bool) or not isinstance(size, int) or size <= 0:
+            if isinstance(size, bool) or not isinstance(size, int) or size < 0:
                 raise InstallError('Invalid lsblk size')
+            empty_optical = (kind == 'rom' and not any(mounts)
+                             and not node.get('children') and node.get('pkname') is None
+                             and ancestor is None)
+            if size == 0 and not empty_optical:
+                raise InstallError('Zero-size device is not an unrelated empty optical drive')
             if not isinstance(identity, str) or not re.fullmatch(r'\d+:\d+', identity):
                 raise InstallError('Invalid lsblk device identity')
             if path in result.nodes and any(result.nodes[path][key] != node[key] for key in ('type', 'size', 'maj:min', 'mountpoints')):
@@ -149,8 +154,13 @@ class Topology:
         for path in directed:
             check_cycle(path)
         for path, node in result.nodes.items():
-            if node['type'] == 'part' and not result.edges[path]:
-                raise InstallError('Partition has no known parent')
+            if node['size'] == 0 and result.edges[path]:
+                raise InstallError('Empty optical drive has block-device dependencies')
+            # An undirected child edge does not establish backing ancestry.
+            # Each layer must identify its own parent, even when another
+            # apparently unrelated disk is the requested installation target.
+            if node['type'] not in {'disk', 'rom', 'loop', 'zram'} and not directed[path]:
+                raise InstallError(f"Device has no known backing parent: {path} ({node['type']})")
         return result
 
     def link(self, child, parent):
@@ -162,6 +172,8 @@ class Topology:
     def protect(self, path):
         if path not in self.nodes:
             raise InstallError(f'Cannot resolve mounted/live source: {path}')
+        if self.nodes[path]['size'] == 0:
+            raise InstallError(f'Empty optical drive unexpectedly backs mounted/live storage: {path}')
         self.protected.add(path)
 
     def component(self, path):