Re: [Xen-devel] [PATCH v5 3/5] libxl: add new pvusb backend "qusb" provided by qemu

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Mar 30, 2016 at 04:34:20PM +0200, Juergen Gross wrote:
> On 30/03/16 16:19, Wei Liu wrote:
> > On Wed, Mar 30, 2016 at 02:05:56PM +0200, Juergen Gross wrote:
> >> Add a new pvusb backend type "qusb" which is provided by qemu. It can
> >> be selected either by specifying the type directly in the configuration
> >> or it is selected automatically by libxl in case there is no "usbback"
> >> driver loaded.
> >>
> >> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> >> ---
> >> V4: bail out in case of usbback_is_loaded() error as requested by
> >>     Chun Yan Liu
> >> ---
> > [...]
> >>  /* Add usbctrl information to xenstore.
> >>   *
> >> - * Adding a usb controller will add a new 'vusb' device in xenstore, and
> >> - * add corresponding frontend, backend information to it. According to
> >> - * "update_json", decide wether to update json config file.
> >> + * Adding a usb controller will add a new 'qusb' or 'vusb' device in 
> >> xenstore,
> >> + * and add corresponding frontend, backend information to it. According to
> >> + * "update_json", decide whether to update json config file.
> >>   */
> >>  static int libxl__device_usbctrl_add_xenstore(libxl__gc *gc, uint32_t 
> >> domid,
> >>                                                libxl_device_usbctrl 
> >> *usbctrl,
> >> @@ -121,6 +144,15 @@ static int 
> >> libxl__device_usbctrl_add_xenstore(libxl__gc *gc, uint32_t domid,
> >>  
> >>          DEVICE_ADD(usbctrl, usbctrls, domid, &usbctrl_saved,
> >>                     COMPARE_USBCTRL, &d_config);
> >> +
> >> +        if (usbctrl->type == LIBXL_USBCTRL_TYPE_QUSB) {
> >> +            if (!libxl__query_qemu_backend(gc, domid, 
> >> usbctrl->backend_domid,
> >> +                                           "qusb", false)) {
> > 
> > This needs to be sorted out.
> 
> What do you mean?
> 

Nothing -- it just meant it depends on a previous patch.

> > And this is maybe a rather dumb question: the xenstore paths for qusb
> > and kernel backend are the same? What is the likelihood that one
> > deviates from the other? Note that this is not suggesting that you
> > over-engineer current code, it's just something that needs clarifying.
> 
> There is an existing pvusb kernel backend implementation in kernel-xen
> of openSUSE and SLE. The port of that implementation hasn't been
> accepted in Linux upstream as it was regarded to fit better in qemu.
> 
> So the qemu base backend is designed in a way to be compatible to the
> already existing kernel backend. Future enhancements will be made on the
> qemu based backend only (as far as SUSE is involved).
> 
> So the frontend related Xenstore paths are the same, while the backend
> paths are different ("vusb" vs. "qusb"). And yes, I've tested the same
> domU with both backends.
> 

Cool, that makes sense.

Wei.

> 
> Juergen
> 

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