> > Also, there is a 'u' hierarchy which is dedicated to whatever the
> > driver wants to do.
> 
> Would you mind explaining just exactly what you mean by this last
> sentence?

By "hierarchy," I was refering to the letter used in the ioctl
definition. Since the letters are used generally to break things up,
it seems appropriate to me. :-)

Line 118 of /sys/sys/ttycom.h defines UIOCCMD(n) to be _IO('u',n) or
a command op code (an ioctl which doesn't transfer data in or out).

>From the way it's worded, I doubt any other part of the kernel will
use a 'u' ioctl. Nothing in /sys/sys does. Thus it strikes me as
fair game for whatever the driver author chooses.

Take care,

Bill