OpenBSD – Introducing Uncm(4)

OpenBSD gained a new USB network-control-mode driver, uncm(4), contributed by Jan Schreiber to support CDC NCM tethering used by newer Android devices (replacing urndis(4) on devices since about Android 6). The submission included a small refactor - moving some defines and structs out of mbim.h into a slimmer usbcdc.h to avoid pulling in the full mobile-broadband headers - so existing umb(4) behavior remained unchanged. After a brief review cycle stsp@ committed the driver to the source tree the next day, reflecting a very fast turnaround from submission to integration.

The driver’s key practical advantage is that it requires no firmware blob, so it can provide network access on machines that otherwise would be stuck waiting for out-of-tree firmware during installation. Because of that property, Stefan added uncm(4) to the amd64 installer kernel ahead of the 8.0 release, enabling users with modern laptops whose wireless cards need firmware to use an Android phone for network access during install. The change removes a catch-22 for such installs and expands out-of-the-box networking options without adding proprietary firmware.