stages/ostree: mode support for mount points

The list of mount points is changed from a list of strings to a
list of objects containing `path` and an optional `mode` value.
The latter can be used to set the mode of the mount point that
will be created in the file system tree. It defaults to 0755,
or 493 in decimal, because JSON does not support octal values.

stages/org.osbuild.ostree

@@ -35,7 +35,19 @@ STAGE_OPTS = """
     "type": "array",
     "items": {
       "description": "Description of one mount point",
-      "type": "string"
+      "type": "object",
+      "required": ["path"],
+      "properties": {
+        "path": {
+          "description": "The path of the mount point",
+          "type": "string"
+        },
+        "mode": {
+          "description": "The mode of the mount point",
+          "type": "integer",
+          "default": 493
+        }
+      }
     }
   },
   "kernel_opts": {
@@ -156,9 +168,10 @@ def main(tree, sources, options):
 
     with MountGuard() as mounter:
         for mount in mounts:
-            path = os.path.join(tree, mount)
-            print(f"mounting {path} onto itself")
-            os.makedirs(path, exist_ok=True)  # FIXME: SELinux
+            path = mount["path"].lstrip("/")
+            path = os.path.join(tree, path)
+            os.makedirs(path, exist_ok=True)
+            os.chmod(path, mount.get("mode", 0o755))
             mounter.mount(path, path)
 
         rootfs_id = make_fs_identifier(rootfs)