That's exactly how I did it too. The biggest hack for me was the 'open' call when using a device. That first does a lookup for a service with the name following the /dev/ bit and then it redirects the 'open' message to that process rather than to the active drive's filesystem. This allows for the appearance of a /dev/ directory without it actually existing anywhere. This makes some Unix like mechanisms hard to implement (for instance, you can't just do 'ls /dev/') but it made enough stuff work out of the box that it seemed worth the trade-off of bypassing the filesystem. It also makes the file system optional, which can come in very handy, because that means no file system is every privileged in the sense of a Unix '/' filesystem. They're all equal and you can kill each and every one of them and still have a running system.