Hello Godfrey, I'm hoping to resurrect discussion about a devfs user client. The initial steps don't look too bad: make a IODevfs extension which can modify devfs and a IODevfsUserClient which issues requests to the extension. Things get trickier with the bdevsw and cdevsw callbacks. It would be nice to provide a fairly-high bandwidth mechanism for moving blocks between the kernel and user land. Also it seems like care should be taken to help prevent a user process from bogging down the kernel. When the callbacks are invoked should they send a mach message describing the event to the user process? The messages could be handled in code provided by the IODevfsUserClient, which would interpret the messages and then make calls into the user process similar to the bdevsw and cdevsw callbacks, maybe even identically, which would allow for easy porting. What are your current thoughts on how to implement the bdevsw and cdevsw callbacks? Thanks, Kevin