Replacing FBSD mutexes

[elekktretterr at exemail.com.au]

> Are you sure it is not used in an ioctl or read/write somewhere?

It's also used in ioctl

> I think in usb4bsd I stored the pointer for one open in the device
> structure.
> Obviously that is not per-fd, but for testing purposes where you only do
> one
> open it was enough.

Ok, I've got a newbie question, what kind of user action will cause
multiple opens on a video device?

Thanks,
Petr