On Sun, 7 Aug 2011, Adam Baker wrote: > I've addec Hans de Geode and linux-usb to the CC as this response picks up on > a related discussion about the usb mini summit. > > On Friday 05 August 2011, Theodore Kilgore wrote: > > > If you can solve the locking problem between devices in the kernel then > > > it shouldn't matter if one of the kernel devices is the generic device > > > that is used to support libusb. > > > > Hmmm. Perhaps not. While we are on the topic, what exactly do you mean by > > "the generic device that is used to support libusb." Which device is that, > > exactly? > > The file drivers/usb/core/devio.c registers itself as a driver called > usb_device which is used to provide all of the device drivers that live under > /proc/bus/usb Let's get things correct. The driver is called usbfs, not usb_device. The things that live under /proc/bus/usb are files representing USB devices, not device drivers. > If you look in there for the code to handle the ioctl() USBDEVFS_DISCONNECT > then you will find the code that is called when you make a > usb_detach_kernel_driver_np() call through libusb. That code, according to the > documentation and my testing needs to acquire a lock before it calls > usb_driver_release_interface(). Based on my testing to date (using cheese to > start a camera streaming and then gphoto2 -L to trigger the disconnect ioctl) > I would suggest that the fact it doesn't is a kernel bug that needs fixing What makes you think the code doesn't acquire the lock? (Hint: Look at usbdev_do_ioctl() instead of proc_ioctl().) > regardless of whether there is any user space solution to camera mode > switching because that code could potentially get called on any in use USB > device and if it does even thing like lsusb don't work correctly afterwards > and completely unrelated devices don't work if they are later plugged into the > same USB port. That's a rather incomprehensible run-on sentence, but as near as I can tell, it is wrong. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
