ioctl group codes.

M

monty_hall

In </dev/usb/usb.h>, I see the following def:

Code: 
#define USB_REQUEST		_IOWR('U', 1, struct usb_ctl_request)

I was wondering what the 'U' (group code per ioccom.h) stood for and then grepped /usr/src for _IOWR and noticed several different group codes. Is there a list or document about ioctl & group codes?

Monty
 
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