About Devfs
Devfs is a virtual filesystem [1] meant to replace the static and ugly /dev pseudo-files. It appeared that having a lot of entries in /dev, "just in case" was not the good approach, neither were the (complicated) scripts to create the entries when needed.
It features a new, cleaner naming pattern (ex.: /dev/hda1 is now /dev/ide/host0/bus0/lun0/part1 ). For obvious compatibility reasons, a daemon, devfsd is available, which can create links with the old filename for devices on-the-fly.
It is dynamic: it will create /dev entries when the modules are loaded and then when the hardware is present. This presents the double [2] benefit of being more readable to human beings, and matching the real hardware on the machine(really useful for USB/IEEE1394/whatever).
It is virtual, and that's what makes it really interesting in read-only root filesystems like Plume uses. It doesn't need write access to the root filesystem, like Plume's alternatives do [3].
Note: Devfs has been obsoleted by Sysfs and Udev in the 2.6 kernel. Most remarks in this article apply to Sysfs also, though.