process_op
.process_op = nfs4_callback_getattr,
.process_op = nfs4_callback_recall,
.process_op = nfs4_callback_layoutrecall,
.process_op = nfs4_callback_devicenotify,
.process_op = nfs4_callback_sequence,
.process_op = nfs4_callback_recallany,
.process_op = nfs4_callback_recallslot,
.process_op = nfs4_callback_notify_lock,
.process_op = nfs4_callback_offload,
__be32 (*process_op)(void *, void *, struct cb_process_state *);
status = op->process_op(rqstp->rq_argp, rqstp->rq_resp,
status = process_op(nops, rqstp, &cps);