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

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

[Gonglei (Arei)]

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!

Best Regards!
-Gonglei

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

[Gerd Hoffmann]

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?

[ qemu uses one global libusb_context.  libusb_device and
  libusb_device_handle are allocated and released on open/close ]

cheers,
  Gerd

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

[Gonglei (Arei)]

> Subject: Re: usb: a problem of using libusb for usb pass through
> 
> 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?
> 
> [ qemu uses one global libusb_context.  libusb_device and
>   libusb_device_handle are allocated and released on open/close ]
> 
> cheers,
>   Gerd
> 

Thanks for responding, Gerd. Would you have a plan to resolve it?

-Gonglei

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

[Hans de Goede]

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

> [ 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() ?

Regards,

Hans

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

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

[Gerd Hoffmann]

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

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

[Gonglei (Arei)]

> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@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
>