Re: [Libusb-devel] OpenUSB / LibUSB on Mac OS X

[Michael L. <mil...@gm...>]

On Tue, Jan 31, 2012 at 11:46 AM, Peter Stuge <pe...@st...> wrote:
> Michael Lewis wrote:
>> I ran across a bug with OpenUSB on Mac OS X 10.7 recently. Basically,
>> I had two processes trying to keep the device open. I looked through
>> the code and found this:
>>
>>   /* Try to actually open the device */
>> #if !defined (OPENUSB_NO_SEIZE_DEVICE)
>>   kresult = (*(hdev->priv->device))->USBDeviceOpenSeize (hdev->priv->device);
>> #else
>>   /* No Seize in OS X 10.0 (Darwin 1.4) */
>>   kresult = (*(hdev->priv->device))->USBDeviceOpen (hdev->priv->device);
>> #endif
>>
>> Is there any reason we can't always just use USBDeviceOpen to prevent
>> exclusive connections? I thought it might have to do with setting the
>> configuration, but my testing shows that the device will work just
>> fine with USBDeviceOpen.
>>
>> So, if there is a reason not to change it, please let me know and I
>> won't, otherwise I will probably submit the change in a few days.
>
> FWIW libusb generally does not enforce exclusive connections, leaving
> the decision up to the kernel. OpenUSB can of course take a different
> approach and that's perfectly fine.

My understanding of the problem is that there are certain operations,
such as setting the configuration, won't work WITHOUT exclusive
access. Currently OpenUSB and libusb-1.0 use the same method to open
the device. I'm not OS X expert, but if we leave things as they are,
is there a way to "seize" the device from another instance in order to
perform operations such as setting the configuration?