Every newly created partition can contain files only from at most one
partition (i.e. up_dircount must be at most 1). Files from the
partition can be contained only in one partition (i.e. it is impossible
to duplicate any data during the whole process). Data from the
partition of FT_UNKNOWN filesystem type can be moved only to a partition
of the same length as the current partition. All limits implicitly
contained in the description above are of course valid as well.