> While I have fussy ideas about the difference between mounts-in-place and
> mounts-elsewhere fs's, we'll need this patch irregardless. :-)
> 
> I think it would be good to adjust mount_null so that it forbids
> 
> mount_null /foo /foo/bar      (or /foo /foo/bar/baz, etc).
> 
> I'm not sure how to do this in the kernel.

Look at sys/kern/vfs_getcwd.c: vn_isunder(); this should be more or
less exactly what you're looking for..

						- Bill