libxl: disks: expose new "script" parameter for external block scripts

This is not currently implemented.  Applications setting it to
anything but NULL will cause an error.  Code to set it from xl
configuration files will appear later in this series.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

tools/libxl/libxl.c

@@ -970,6 +970,13 @@ int libxl_device_disk_add(libxl_ctx *ctx, uint32_t domid, libxl_device_disk *dis
         goto out_free;
     }
 
+    if (disk->script) {
+        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "External block scripts"
+                   " not yet supported, sorry");
+        rc = ERROR_INVAL;
+        goto out_free;
+    }
+
     devid = libxl__device_disk_dev_number(disk->vdev, NULL, NULL);
     if (devid==-1) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Invalid or unsupported"

tools/libxl/libxl.idl

@@ -279,6 +279,7 @@ libxl_device_disk = Struct("device_disk", [
     ("vdev", string),
     ("backend", libxl_disk_backend),
     ("format", libxl_disk_format),
+    ("script", string),
     ("unpluggable", integer),
     ("readwrite", integer),
     ("is_cdrom", integer),