My perspective on this is that disklabels and partitions are a protozoic kind of file system -- essentially, that the way to think about what needs to happen is that you need to mount `partitionfs' on the device /dev/wd0. This `mount' then supplies the other wd0* devices. (Whether it goes through the same code path as normal filesystem mounts, or looks at all like them, is unimportant. Bear with me.)

This view of the world has two immediate consequences: 1) partition handling should be independent from disk drivers. 2) probing for partitions becomes relatively straightforward.