2013/3/22 Hans de Goede <hdego...@redhat.com>: > Although automatic detaching may seem like a smart and user (programmer) > friendly thing to do, I'm very much against it! Let me explain > why: > > a) libusb_detach_kernel_driver on Linux will *always* work if the > user has the necessary rights on the usbfs device node > > b) When libusb_detach_kernel_driver is done, the driver sees a > device unplug, iow it is to the driver as if the user janked out > the device. > > Combine these 2 and now try to run some generic libusb using tool, > on a system with liberally set up usbfs permissions, then the following > could happen: > i) user is using a usb-stick, copies a large file to it > ii) user runs the libusb tool > iii) the tool detaches the usb-mass-storage driver before all cached > writes are flushed -> data and/or filesystem damage > > Not good. Now this can already happen, but making the driver detach > automatic (by default) makes it that much easier to happen, so strong > NACK to that idea.
Another example: Your application uses libusb with automatic detach. You start the application and let it run. You forget about it but it is still running. Then you start the same application again. Instead of failing at the claim, the second execution will call detach and break the first execution of the application that was still running and using the device. This is BAD. Yes, it already happened to me. On Linux, I think it is much more safe to use a udev rule to detach the HID kernel driver, and set the correct access rights, when the device is plugged. Like what I did at [1]. On a developpement system you can play with libusb_detach_kernel_driver(). That is fine. But on a production system I think it is too dangerous. So I propose to NOT add an automatic detach. Bye [1] http://libusb.6.n5.nabble.com/Automatic-detach-of-a-HID-device-using-udev-Re-How-to-dump-HID-report-descriptor-under-Linux-td3330260.html#a3334978 -- Dr. Ludovic Rousseau ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_mar _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
