On Mon, 5 Nov 2012, Linus Walleij wrote: > Hi, > > we had the following problem in libmtp: > > - We have to autoprobe every plugged-in device to figure out if it is > MTP or not. These devices are numerous and we can no longer > count on users reporting each and every VID+PID out there > > - Class codes cannot be used > > - Have to look for devices with interfaces with certain endpoints: > - 1 BULK in > - 1 BULK out > - 1 INTERRUPT in > > - Then we do deeper probing. > > - However some devices bug out on libusb_open() which is in turn > needed to use libusb to figure out if the interface has these > BULK and INTERRUPT characteristics > > So since I cannot use libusb_open() I have added code like below > to libmtp to instead inspect sysfs *before* starting any libusb-based > business. It is run from udev and udev provides the sysfs node and > that is passed to check_sysfs(). > > So: > > - Is this a good idea? It's perfectly fine and should work okay. > - What is the scary business that libusb_open() does that makes > a lot of substandard USB devices totally freak out? I have no idea. As far as I know, libusb_open() doesn't do any communication with the device. Try collecting a usbmon trace to see what libusb is doing. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
