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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/18/2013 12:20 PM, Bei Guan wrote:
> Hi,
>
> Thank you very much for your reply. I will reply inline.
>
> 2013/6/18 Ian Campbell <Ian.Campbell@xxxxxxxxxx
> <mailto: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).
> 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?
> It seem that I have never seen the usb device in DomU's XenStore
> entries, even for PV and HVM.
>
>
> 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.
>
>
>     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?
To use PVUSB you need:
1. A backend dom0 (or other driver domain) with usbback
2. A domU with usbfront
3. A toolstack that can connect them together.

It sounds like you're trying to implement #2 for FreeBSD -- that's 
great, but not strictly necessary if you're running in PVHVM mode.
Unfortunately the only kernels that satisfy #1 at the moment, as far as 
we know, are the "classic Xen" kernels being forward-ported by SuSE. 
You should be able to "lsmod" and grep for "usbback" (or "xen" and see 
if there's anything with "usb" in it) to check if your kernel supports 
it or not.
Regarding #3, xend/xm can do it, but xl cannot yet.  (This is planned 
for 4.4).
I think the "third kind of pass-through" Ian may be talking about is 
hot-plug.  At the moment, xl does not support USB hot-plug for HVM 
guests; you have to specify all USB devices in the config file before 
booting.  (xm will support hot-plug for qemu-traditional I think, but 
not for qemu-xen, AFAIK.)
 -George

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