USB Question: unable to open /dev/ugen0 more than once

Bernd Walter ticso at
Mon Nov 24 05:54:51 PST 2003

On Sun, Nov 23, 2003 at 08:50:45PM -0500, Michael E. Mercer wrote:
> Hello peoples,
> I posted this to questions with no reply, I was hoping 
> someone here may be able to give some insight.
> Question: Should I be able to open /dev/ugen0 more than once?
> I am using FreeBSD 4.9-Stable, libusb-0.1.7.
> >From reading the libusb docs, you must open the device for each
> interface you want to acquire. However, once it is opened once, it can't
> be opened again. 
> Furthermore, calls to usb_find_devices() shows that /dev/ugen0 has
> disappeared. Investigation on how they(libusb) finds devices, shows they
> are trying to open the device read only... this is where it tries to
> open it the second time. This second try fails and therefore libusb
> thinks the device was removed.
> Question: Is this the correct behavior?

Yes - this is correct.
A client using ugen on a multiple interface only need to open
/dev/ugen? for probing only - the work should be done using the
interface specific endpoints /dev/ugen?.?
Opening /dev/ugen? read-only makes no sense, because there is no read
only access possible - /dev/ugen? is for the control endpoint which
always means sending commands to the device.

B.Walter                   BWCT      
ticso at                                  info at

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