req_sync
xbdreq->req_sync.s_done = 0;
while (xbdreq->req_sync.s_done == 0)
if (xbdreq->req_sync.s_error == BLKIF_RSP_EOPNOTSUPP)
else if (xbdreq->req_sync.s_error == BLKIF_RSP_OKAY)
} req_sync;
#define req_sync u.req_sync
xbdreq->req_sync.s_error = rep->status;
xbdreq->req_sync.s_done = 1;