libxl: 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.

This patch will check emptiness of usbdevice_list. And NULL is still a
valid empty list.

Signed-off-by: Robin Lee <robinlee.sysu@gmail.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index f8ba8599e5ec5f0054c67e78efdf25d33fa36293..44ebd7063c75b94a3e0db553e4209f14825deeeb 100644 (file)
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -559,9 +559,9 @@ 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) {
-            if ( 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
+                && libxl_string_list_length(&b_info->u.hvm.usbdevice_list)) {
                 LOGD(ERROR, domid, "Both usbdevice and usbdevice_list set");
                 return ERROR_INVAL;
             }
@@ -1149,9 +1149,9 @@ 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) {
-            if ( 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
+                && libxl_string_list_length(&b_info->u.hvm.usbdevice_list)) {
                 LOGD(ERROR, guest_domid, "Both usbdevice and usbdevice_list set");
                 return ERROR_INVAL;
             }