qcow2 supports backing files so it makes sense to default to qcow2 for MIRROR_SYNC_MODE_NONE so that we can use the source as a backing drive and export it via nbd. Defaulting FULL and TOP to SYNC_MODE_NONE breaks tests but that could be fixed if we wanted it.
Signed-off-by: Ian Main <im...@redhat.com> --- blockdev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/blockdev.c b/blockdev.c index 000dea6..805b0e5 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1462,7 +1462,7 @@ void qmp_drive_backup(const char *device, const char *target, } if (!has_format) { - format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name; + format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2"; } if (format) { drv = bdrv_find_format(format); -- 1.8.1.4