Subject: Re: creating new ioctls
To: Michael Graff <>
From: Bill Studenmund <>
List: tech-kern
Date: 08/05/1997 10:37:35
> Am I right in assuming that so long as the starting letter (in this
> case "I") is unique across the system, you can create whole new groups
> of ioctls?
> I ask since I'm starting to hack on the random device, and would like
> to have a few ioctls to get snapshots of some data while debugging and
> in production.

Actually, I think it only needs to be unique among all the interveening
steps the ioctl covers. If you have a tty device, you need to look out
for the 't' ioctls (tty subsystem). Socket devices need to watch out
for the socket family, etc.

The difference is that, if you made a character device which didn't use
the tty system, you could re-use the 't' ioctl's. It'd be sick &
confusing, but it'd work.

Also, there is a 'u' hierarchy which is dedicated to whatever the
driver wants to do.

Take care,