On 07/30/13 19:13, Hans de Goede wrote: > Hi, > > On 07/22/2013 02:58 PM, Gerd Hoffmann wrote: >> On 07/16/13 10:45, Gonglei (Arei) wrote: >>> Hi, Gerd >>> My Qemu version is 1.5.1, and use libusb for usb pass through. >>> I pass through a host usb device to the guest by bus number and >>> physical port, when I unplug the usb device from >>> the host, and plug in on the same physical port immediately, but the >>> usb device don't show up in the guest. >>> The qemu log show: >>> libusb_release_interface: -4 [NO_DEVICE] >>> libusbx: error [_get_usbfs_fd] libusbx couldn't open USB device >>> /dev/bus/usb/002/004: No such file or directory >>> libusbx: error [_get_usbfs_fd] libusbx couldn't open USB device >>> /dev/bus/usb/002/004: No such file or directory >>> libusbx: error [_get_usbfs_fd] libusbx couldn't open USB device >>> /dev/bus/usb/002/004: No such file or directory >>> >>> I find the reason is that the global libusb_context has recorded >>> the usb devices' devnum, but when the host device was unplugged and >>> plugged >>> from the host, the devnum will change, finally cause the problem. >>> Any ideas ? Thanks! >> >> Sounds like libusbx doesn't flush the cache on unplug even though it >> should. Hans? > > This looks like qemu's host-libusb code is re-using the libusb_device > handle, what it should do after seeing an > unplug (ie ENODEV error), it should close both the handle, and free any > devices it may have, then redo > the libusb_get_device_list() and you should get a libusb_device with the > new address. This is what the > usb code in the spice-client does, and it has no problems with sc
host-libusb.c doesn't do that, and I also can't reproduce the issue. Running libusbx-1.0.14 at the moment. I get slightly different errors: libusb_release_interface: -4 [NO_DEVICE] libusbx: error [_open_sysfs_attr] open /sys/bus/usb/devices/10-1/bConfigurationValue failed ret=-1 errno=2 Which comes from host-libusb trying to release the (unplugged) device on closing. They are harmless. >> [ qemu uses one global libusb_context. libusb_device and >> libusb_device_handle are allocated and released on open/close ] > > That is fine, do you also free the device_list, and re-do the > libusb_get_device_list() ? Sure. Each time it looks for new devices it calls libusb_get_device_list(). cheers, Gerd