Re: [Qemu-devel] usb: a problem of using libusb for usb pass through

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 07/30/2013 07:13 PM, 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

That should have read: "it has no problems with this scenario"

Regards,

Hans