configuration routine has been attached to the putter device minor
number, the configuration routine will be called when the device
is opened. This is required for subsystems which enter the kernel
only through the file descriptor and cannot configure themselves
via another route (like puffs does via the mount() syscall). Keep
the minor number 0 for "wildcard" uses where we do not require a
hardwired config routine (e.g. the puffs case).
