Memory Mapping Overview
The steps that a driver must take to export device or kernel memory
are as follows:
Set the D_DEVMAP flag in the cb_flag flag of the cb_ops(9S) structure.
Define a devmap(9E) driver
entry point and optional segmap(9E) entry
point to export the mapping.
Use devmap_devmem_setup(9F) to set up
user mappings to a device. To set up user mappings to kernel memory, use devmap_umem_setup(9F).