Am Dienstag, 12. Januar 2010 22:08:22 schrieb Hans de Goede: > Well libgphoto2 politely asks the kernel, can you please release usb device > foo for userspace use ? I'm asking for drivers to have the possibility to > say: No sorry, the device is in use. > > This does not seem something strange to me. This can be hacked around > in libgphoto by: > > 1) Adding code to match the usb device to a /dev/video > 2) If it matches a /dev/video, open that (this will work multiple opens > are allowed) > 3) Try to start a stream (yes because we really want libgphoto2 to > have to start the webcam) > 4) If 3) fails with ebusy, an other app is already streaming, don't ask > the kernel to release the device. > 5) If 3) does not fail, close the device and continue If you do it that way, you'll create a race. You have to kick yourself off the device. > That would be a gross hack, but that would be the way to "fix" libgphoto2 . This works only if we can reliably locate all affected device nodes. Hans, does libgphoto2 need to kick off all drivers or just the driver for the video interface? > Or we could have the please release the device call return -EBUSY, which > almost every other single syscall in the kernel will do when a single use > device is already in use by another application. If we do this unconditionally blocking disconnect is a bad idea. We'd better introduce a new ioctl, like USBDEVFS_RELEASE_IDLE_INTERFACE, to lave user space the option to kick a driver off a busy device. Regards Oliver -- 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
