The filesystem //foo/bar is specified in /etc/fstab as mountable on /bar,
with options "user,noauto".
This fails, because smbmount isn't installed setuid.
When this is fixed, the operation fails with message "failed to unmount
/bar" (this is not a partition, just an empty directory).
There are (last time we checked) a couple of races still in smbmount,
so it's not setuid. The 'device or resource busy' is because
if the smbmount fails, the directory is left in a 'half-mounted'