Needed for mount(8) to lookup LABEL=* in /dev/disk/by-label/*. Characters
not suited for a filename will be escaped and the encoded LABEL=* string
is able to find the corresponding symlink.
In a future version of libvolume_id, struct volume_id will be
an opaque data type, which can't be accessed directly.
No interface has changed for now, until all known users are
converted not to access the structure directly.
Some broken usb-storage devices implement multiple
luns with all the same SCSI identifiers. Append the
target:lun to get unique names in /dev/disk/by-id/.