# ioctl group codes.



## monty_hall (Jul 3, 2009)

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


```
#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


----------

