Re: [Xen-devel] [PATCH] libxl/libxl_dm.c: u.hvm.usbdevice_list is checked for emptiness

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Robin Lee writes ("[PATCH] libxl/libxl_dm.c: u.hvm.usbdevice_list is checked 
for emptiness"):
> Currently usbdevice_list is only checked for nullity. But the OCaml binding
> will convert empty list to a pointer to NULL, instead of a NULL pointer. That
> means the OCaml binding will fail to disable USB.

Thanks for this.

> This patch will check emptiness of usbdevice_list. And NULL is still a valid 
> empty list.
> 
> Signed-off-by: Robin Lee <robinlee.sysu@xxxxxxxxx>
> ---
>  tools/libxl/libxl_dm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> index f8ba859..a76a438 100644
> --- a/tools/libxl/libxl_dm.c
> +++ b/tools/libxl/libxl_dm.c
> @@ -559,7 +559,7 @@ static int libxl__build_device_model_args_old(libxl__gc 
> *gc,
>          }
>          if (libxl_defbool_val(b_info->u.hvm.usb)
>              || b_info->u.hvm.usbdevice
> -            || b_info->u.hvm.usbdevice_list) {
> +            || libxl_string_list_length(&b_info->u.hvm.usbdevice_list)) {
>              if ( b_info->u.hvm.usbdevice && b_info->u.hvm.usbdevice_list )
>              {

I think it would be better to add this string_list_length in the
conflict check in the next line.  That way if someone (eg in ocaml)
specifies usbdevice but not usbdevice_list it will still work.

>                  LOGD(ERROR, domid, "Both usbdevice and usbdevice_list set");
> @@ -1149,7 +1149,7 @@ static int libxl__build_device_model_args_new(libxl__gc 
> *gc,
>          }
>          if (libxl_defbool_val(b_info->u.hvm.usb)
>              || b_info->u.hvm.usbdevice
> -            || b_info->u.hvm.usbdevice_list) {
> +            || libxl_string_list_length(&b_info->u.hvm.usbdevice_list)) {
>              if ( b_info->u.hvm.usbdevice && b_info->u.hvm.usbdevice_list )

The similarity between the existing code here, and at the previous
site of the bug, is quite striking, isn't it.

Thanks,
Ian.

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