Read-only bind mounts

It is also usefull in backup sitution, when you want users to have access to backup data, but
readonly. Because backuping data needs write access to partition which holds backup, and
probably you want to save space using hardlinking you must have both read-write access for
root, and read only for users because backuped data have orginal permissions which can state
that user have read-write access to them (this is bad because, if files are hardlinked beetwen
snapshots file modifications can destroy previous snapshots! and stupid users can also destroy
own backups, which is also bad :D ).

Very usefull feature.