libxl: prefer qdisk over blktap when choosing disk backend

There are some disk formats commonly supported by both qdisk and blktap.
As qdisk is better supported and blktap is unmaintained, we choose qdisk
over blktap whenever possible.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index ea845b733475b0e7de44178b54becaf04447c81c..16a92a4bec7e71e98dbd24fa54499a1bdd9f5e4d 100644 (file)
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -288,8 +288,8 @@ int libxl__device_disk_set_backend(libxl__gc *gc, libxl_device_disk *disk) {
     } else {
         ok=
             disk_try_backend(&a, LIBXL_DISK_BACKEND_PHY) ?:
-            disk_try_backend(&a, LIBXL_DISK_BACKEND_TAP) ?:
-            disk_try_backend(&a, LIBXL_DISK_BACKEND_QDISK);
+            disk_try_backend(&a, LIBXL_DISK_BACKEND_QDISK) ?:
+            disk_try_backend(&a, LIBXL_DISK_BACKEND_TAP);
         if (ok)
             LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Disk vdev=%s, using backend %s",
                        disk->vdev,