XBP_FB
fb_exists = xenbus_exists(xsname, XBP_FB);
(err = xenbus_printf(xbt, xsname, XBP_FB, "%d", 1)))) ||
if (((err = xenbus_rm(xbt, xsname, XBP_FB)) != 0) ||
if (!(vdp->xdf_feature_barrier = xenbus_exists(oename, XBP_FB)))