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

[Wei Liu <wei.liu2@citrix.com>]

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@suse.com>
> ---
> 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.

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.

Wei.

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