actually, it's not too hard to have an ether*.c that opens a USB
device configured by user space and interacts with it.  the Inferno
driver that does just that is simpler than some of the other drivers
in some ways.  there's a fair amount of flexibility using
Etherif->ctl.  the harder part is dealing with the wretch on the other
end of the USB (eg, configuring it).  fortunately, that can be in user
space, which is good because it's a fair amount of code, and that's in
Limbo not C.

i don't see why an etheruser.c should be that tricky, but then again, i
haven't thought about it much, although i did consider it once as potentially
useful for several applications.