15.1  Unload Routine Requirements

Any NT driver that can be replaced, or unloaded and reloaded, while Windows NT® is running must have an Unload routine.

NT drivers for video, keyboard, or mouse devices, and for mass-storage devices that can hold the system page file currently do not have Unload routines because these types of devices must be available while the current system is running. Higher-level NT drivers layered above these device drivers also do not have Unload routines.

Like every DriverEntry routine, an Unload routine runs at IRQL PASSIVE_LEVEL and is called in the context of a system thread.

In general, the process of unloading a driver is a synchronous operation.