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

[Hans de Goede]

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