Ian Campbell wrote:
if (l_disk->driverName) { ... } else { /* No driverName - default to raw/tap?? */ x_disk->format = LIBXL_DISK_FORMAT_RAW; x_disk->backend = LIBXL_DISK_BACKEND_TAP; }
I recall some discussion about the choice of these defaults, but can't find anything in the xen or libvirt ml archives. We can adjust the defaults (or defer to libxl?) if it makes sense. I took a quick peek at newer libxl code (recall this was written against Xen 4.1 libxl) and perhaps 'x_disk->backend = LIBXL_DISK_BACKEND_QDISK' would be a saner default? Adding Ian to help with this question...
LIBXL_DISK_BACKEND_UNKNOWN will cause libxl to pick the best available (which includes checking if blktap is actually there) backend given the format and file type (block device, file etc). That's probably the right default.
Ok, thanks.
libxl__device_disk_set_backend is the guy to look at if you are interested how the selection happens.
After taking a peek, agreed that LIBXL_DISK_BACKEND_UNKNOWN is a better backend default. I'll leave the format default of LIBXL_DISK_FORMAT_RAW to be consistent with $xen-src/docs/misc/xl-disk-configuration.txt. Thanks, Jim