Re: [Xen-devel] [PATCH 5/6] libxl: add HVM usb passthrough support

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Sep 09, 2016 at 12:13:46PM +0200, Juergen Gross wrote:
> On 09/09/16 12:00, Wei Liu wrote:
> > On Thu, Sep 08, 2016 at 09:20:25AM +0200, Juergen Gross wrote:
> >> Add HVM usb passthrough support to libxl by using qemu's capability
> >> to emulate standard USB controllers.
> >>
> >> A USB controller is added via qmp command to the emulated hardware
> >> when a usbctrl device of type DEVICEMODEL is requested. Depending on
> >> the requested speed the appropriate hardware type is selected. A host
> >> USB device can then be added to the emulated USB controller via qmp
> >> command.
> >>
> >> Removing of the devices is done via qmp commands, too.
> >>
> >> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > [...]
> >>  
> >> @@ -75,9 +131,19 @@ static int libxl__device_from_usbctrl(libxl__gc *gc, 
> >> uint32_t domid,
> >>  {
> >>      device->backend_devid   = usbctrl->devid;
> >>      device->backend_domid   = usbctrl->backend_domid;
> >> -    device->backend_kind    = (usbctrl->type == LIBXL_USBCTRL_TYPE_PV)
> >> -                              ? LIBXL__DEVICE_KIND_VUSB
> >> -                              : LIBXL__DEVICE_KIND_QUSB;
> >> +    switch (usbctrl->type) {
> >> +    case LIBXL_USBCTRL_TYPE_PV:
> >> +        device->backend_kind = LIBXL__DEVICE_KIND_VUSB;
> >> +        break;
> >> +    case LIBXL_USBCTRL_TYPE_QUSB:
> >> +        device->backend_kind = LIBXL__DEVICE_KIND_QUSB;
> >> +        break;
> >> +    case LIBXL_USBCTRL_TYPE_DEVICEMODEL:
> >> +        device->backend_kind = LIBXL__DEVICE_KIND_NONE;
> > 
> > I'm not quite sure if I follow this. Shouldn't we need a new kind of
> > backend for this?
> 
> Depends on what do you call a backend.
> 
> I'd say a backend is something which corresponds to a frontend in the
> guest. As long as you don't want to call a normal hardware driver a
> "frontend" we don't need a backend.
> 
> At least the "backend" (qemu, requiring no update for this) won't use
> Xenstore for detecting addition/removal of devices: all is done via
> explicit qmp commands issued from libxl to qemu.
> 

After having a closer look, this is internal detail of libxl so I don't
think I care that much.

I will review this patch in detail later.

Wei.

> 
> Juergen

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