int devmap_unload(devmap_cookie_t handle, offset_t offset, size_t len);
devmap_unload(9F) invalidates the mapping translations for the pages of the mapping specified by handle, offset, and len. By invalidating the mapping translations for these pages, the device driver is telling the system to intercept accesses to these pages of the mapping and notify the device driver the next time these pages of the mapping are accessed by calling the devmap_access(9E) entry point.
For both functions, requests affect the entire page containing the offset and all pages up to and including the entire page containing the last byte, as indicated by offset + len. The device driver must ensure that for each page of device memory being mapped only one process has valid translations at any one time.
Both functions return zero if they are successful. If, however, there was an error in validating or invalidating the mapping translations, that error is returned to the device driver. It is the device driver's responsibility to return this error to the system.