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Re: [Xen-users] How to present the vusb device entry in the xenstore

2013/6/18 Ian Campbell <Ian.Campbell@xxxxxxxxxx>
On Tue, 2013-06-18 at 19:20 +0800, Bei Guan wrote:
> Hi,
> Thank you very much for your reply. I will reply inline.
> 2013/6/18 Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>         On Tue, 2013-06-18 at 08:51 +0800, Bei Guan wrote:
>         > Hi,
>         >
>         >
>         > I'd like to use the pvusb device in xen-4.3 unstable.
>         However, when I
>         > use the command "xenstore-ls /local/domain/domId/device" in
>         my VM,
>         > there's no "vusb" device presented.
>         Which toolstack are you using?
>         Which kind of guest (PV or HVM or PVHVM) is it? Which kernels
>         are you
>         using in dom0 and domU?
>         I'm not sure which (emulated USB device passthrough or full PV
>         USB) you
>         are referring to as "vusb".
> I use the xl tools and the guest is FreeBSD (It's PVHVM). I think
> other PVHVM DomUs are also the same. The dom0 is linux
> 2.6.32-5-xen-amd64 or linux 3.9.1 x86_64 (both the same for me).

As far as I know neither of these have PV USB (either Front or Back)
Does the following kernel support USB front driver and USB backend now?
I see that there are /drivers/xen/usbback and /drivers/xen/usbfront in the code tree.

If it doesn't support or its USB PV drivers don't work well, how can I write the USB front driver for a PVHVM guest, such as FreeBSD?

Thank you very much.


The Linux versions of these drivers were never upstreamed. I don't know
if they even existed at all for FreeBSD.

> I just want to know how to make the USB frontend and backend drivers
> to work correctly for a PVHVM DomU.
> If the DomU uses the emulated USB devices presented by xen-qemu, the
> USB frontend and backend drivers will not work. And, the usb devices
> for DomU cannot be seen in the XenStore. Is it right?

I don't think so, I can't see why an emulated USB controller and a PV
USB controller shouldn't be able to coexist.

> It seem that I have never seen the usb device in DomU's XenStore
> entries, even for PV and HVM.

If you are using qemu based passthrough then there won't be any nodes in
xenstore since it is not PV based.

> I'd like to add a PVUSB front driver for FreeBSD, so I need to make
> sure that the PVUSB device is added by DomU's XenBus driver and the
> PVUSB backed driver in Dom0 works well.
> However, it seems that the PVHVM DomU always uses the USB hardware
> emulated by xen-qemu. So my PVUSB front driver cannot probe the PVUSB
> device.

That's right, because the dom0 kernel and toolstack you are using both
don't support PVUSB.

I think your only option at this point is the Qemu provided passthrough.

>         AFAIK for xl in 4.3 only USB passthrough to HVM domains via
>         device model
>         emulation of the host controller is supported.
>         Support for PVUSB is on the cards for 4.4 I think, although
>         AIUI it is
>         somewhat blocked on someone stepping up and taking
>         responsibility for
>         the PVUSB driver side of things.
> Do you mean that before the Xen 4.4, there are no xen versions
> supporting the the PVUSB frontend and backend dirvers?
> If I want to use the PVUSB, I need to move on to Xen 4.4?

Front and backend drivers come from your kernels not from Xen. Remember
than Xen doesn't ship any kernels these days.

My comment about 4.4 related to the provision of toolstack support for
PV USB, which as I say is contingent on someone also upstreaming the
front and backend drivers.


Best Regards,
Bei Guan
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