Aleksa Sarai [off-list ref]:

+mntfd2 = open_tree(mntfd1, "", OPEN_TREE_CLONE,
+                   &attr, sizeof(attr));

Your whole so-called "open_tree_attr example" doesn't contain any open_tree_attr
calls. :)

I think you meant open_tree_attr here.

+\&
+/* Create a new copy with the id-mapping cleared */
+memset(&attr, 0, sizeof(attr));
+attr.attr_clr = MOUNT_ATTR_IDMAP;
+mntfd3 = open_tree(mntfd1, "", OPEN_TREE_CLONE,
+                   &attr, sizeof(attr));

And here.

Otherwise your whole patchset looks good. Add to whole patchset:
Reviewed-by: Askar Safin <redacted>

-- 
Askar Safin