libftdi Archives

Subject: Re: Claiming devices has no effect under Linux

From: Thomas Klose <thomas.klose@xxxxxxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 05 Oct 2010 15:51:33 +0200
Am Dienstag, den 05.10.2010, 15:20 +0200 schrieb Thomas Jarosch: 
> On Tuesday, 5. October 2010 14:35:25 Thomas Klose wrote:
> > If I open a ftdi device in an instance of our application it seems not
> > to be claimed for exclusive access. A second instance of the application
> > can "steal" the device later.
> > 
> > I found in the sources of libftdi that the libusb function
> > usb_claim_interface() is called correctly by ftdi_usb_open_dev(). It was
> > my understanding that usb_claim_interface() marks the device to be "in
> > use" and a second call would result in an appropriate error.
> Well, the function does what it's named after: Claim the device, no matter 
> who is currently using it: Kernel driver or another libftdi instance.
Sorry, I do not understand. Does this mean, when a device is
successfully claimed, it always can be used by other instances?

If this is the case, is there a possibility to signal the other instance
that the device is already in use, e.g. get usb_claim_interface() to
return -EBUSY?

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