While geom_flashmap has always supported label names for its slices, it does so by appending "s.labelname" to the provider device name, meaning you still have to know the name and unit of the hardware device to use the labels.
These changes add support for device-independent geom_flashmap labels, using the standard geom_label infrastructure. geom_flashmap now creates a softc struct attached to its geom, and as it creates slices it stores the label into an array in the softc. The new geom_label_flashmap uses those labels when tasting a geom_flashmap provider.