[PATCH 07/14] libxl: disks: Make LIBXL_DISK_BACKEND_UNKNOWN work

[Ian Jackson <ian.jackson@eu.citrix.com>]

libxl callers should not be required to specify the backend if they
don't want to.  So LIBXL_DISK_BACKEND_UNKNOWN should instruct libxl to
choose the backend for itself.

More thorough fixes for the disk handling will follow.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
 tools/libxl/libxl.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index fe012cb..73fc3e9 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -989,6 +989,21 @@ int libxl_device_disk_add(libxl_ctx *ctx, uint32_t domid, libxl_device_disk *dis
     device.domid = domid;
     device.kind = DEVICE_VBD;
 
+
+    /*
+     * Fixing the incoming backend type to try to decide on which
+     * backend to use.  Unfortunately at the moment this code is
+     * utterly broken, but it more or less works.
+     */
+
+    /*
+     * Backend type UNKNOWN should mean "caller does not want to specify",
+     * not "break pointlessely".  (Callers should not be required to
+     * specify the backend if they don't want to.)
+     */
+    if (disk->backend == LIBXL_DISK_BACKEND_UNKNOWN)
+        disk->backend = LIBXL_DISK_BACKEND_TAP;
+
     /* If blktap is not available then fallback to qdisk */
     if (disk->backend == LIBXL_DISK_BACKEND_TAP && !libxl__blktap_enabled(&gc))
         disk->backend = LIBXL_DISK_BACKEND_QDISK;
-- 
1.7.2.5