> -----Original Message----- > From: Gerd Hoffmann [mailto:kra...@redhat.com] > Sent: Wednesday, July 31, 2013 5:47 PM > To: Hans de Goede > Cc: Gonglei (Arei); qemu-devel@nongnu.org; Luonengjun; Huangweidong > (Hardware); Linqiangmin > Subject: Re: usb: a problem of using libusb for usb pass through > > 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. >
Hi, Gerd. I was using libusbx-1.0.16 when I reported that overhead problem. -Gonglei > 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 >
