I have a USB HID device with a surreally annoying interface, which essentially
depends on the knowledge that Windows has a fairly short buffer for inbound
messages.

This would be a tailor-made application for the USB_GET_REPORT ioctl, but the
device doesn't support it.

So, I need some way to either:
1.  Flush the USB device's input buffer on command.
or
2.  Have the driver flush things fairly aggressively automatically.

My current hack is, right before accepting bytes in uhid_intr, to call
ndflush on sc->sc_q, and flush a whole lot of bytes.  It works, but it's
clearly ugly and probably wrong for every device out there.

The USB_SET_IMMED ioctl would be great, except it doesn't work on this device
because USB_GET_REPORT doesn't.

One proposal comes to mind; add an automatic ndflush() call to the
USB_SET_IMMED ioctl, which is applied before the check to make sure immediate
mode works.  I am pretty sure this would never be wrong for users who really
want immediate mode; after all, once the device is in immediate mode, the
queue is never used, so flushing it is harmless.

Second opinions?

-s