The libxl driver was setting the backend field of libxl_device_disk structure to LIBXL_DISK_BACKEND_TAP when the driver element of disk configuration was not specified. This needlessly forces the use of blktap driver, which may not be loaded in dom0 https://bugzilla.redhat.com/show_bug.cgi?id=912488 Ian Campbell suggested that LIBXL_DISK_BACKEND_UNKNOWN is a better default in this case https://www.redhat.com/archives/libvir-list/2013-February/msg01126.html --- src/libxl/libxl_conf.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c index 43fb8b1..4ce5dec 100644 --- a/src/libxl/libxl_conf.c +++ b/src/libxl/libxl_conf.c @@ -525,9 +525,13 @@ libxlMakeDisk(virDomainDiskDefPtr l_disk, libxl_device_disk *x_disk) return -1; } } else { - /* No driverName - default to raw/tap?? */ + /* + * If driverName is not specified, default to raw as per + * xl-disk-configuration.txt in the xen documentation and let + * libxl pick a suitable backend. + */ x_disk->format = LIBXL_DISK_FORMAT_RAW; - x_disk->backend = LIBXL_DISK_BACKEND_TAP; + x_disk->backend = LIBXL_DISK_BACKEND_UNKNOWN; } /* XXX is this right? */ -- 1.8.0.1