MBR Non-Linear Extended Partitions
Extended partitions contain a linked list of logical partitions, which may not always be linear. libmount currently requires the list to be linear. If non-linearness is to be accepted, then disked(8) isn't ready for it. It expects the ebr chain to be linear for the purpose of locating holes. It also expects linearness during logical partition creation and removal. It's unclear if extended partitions are supposed to be linear and how allowed non-linearness is. Parsing would need to take care to avoid overlaps and avoid infinite loops. If nonlinearness is unreasonable, disked should possibly have a fixebr command that reorders the ebr linked list to be linear. Note that this will change the device names and may prevent some operating systems from booting. People really need to switch to GPT.
@Uityyy had such a case in the report in bug #61 (closed).