On Fri, Jan 22, 2021 at 06:33:40PM +0100, Christoph Hellwig wrote:

quoted

 /*
  * mount_setattr()

@@ -127,9 +128,10 @@ struct mount_attr {
 	__u64 attr_set;
 	__u64 attr_clr;
 	__u64 propagation;
+	__u64 userns_fd;
 };
 
 /* List of all mount_attr versions. */
-#define MOUNT_ATTR_SIZE_VER0	24 /* sizeof first published struct */
+#define MOUNT_ATTR_SIZE_VER0	32 /* sizeof first published struct */

I think this hunk needs to go into the patch adding the structure.

But except for that the patch looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>