nfs41: back channel drc minimal implementation

For now the back channel ca_maxresponsesize_cached is 0 and there is no
backchannel DRC. Return NFS4ERR_REP_TOO_BIG_TO_CACHE when a cb_sequence
cachethis is true.  When it is false, return NFS4ERR_RETRY_UNCACHED_REP as the
next operation error.

Remember the replay error accross compound operation processing.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/callback_proc.c

@@ -143,9 +143,8 @@ int nfs41_validate_delegation_stateid(struct nfs_delegation *delegation, const n
  * Return success if the sequenceID is one more than what we last saw on
  * this slot, accounting for wraparound.  Increments the slot's sequence.
  *
- * We don't yet implement a duplicate request cache, so at this time
+ * We don't yet implement a duplicate request cache, instead we set the
- * we will log replays, and process them as if we had not seen them before,
+ * back channel ca_maxresponsesize_cached to zero. This is OK for now
- * but we don't bump the sequence in the slot.  Not too worried about it,
  * since we only currently implement idempotent callbacks anyway.
  *
  * We have a single slot backchannel at this time, so we don't bother
@@ -174,9 +173,15 @@ validate_seqid(struct nfs4_slot_table *tbl, struct cb_sequenceargs * args)
 
 	/* Replay */
 	if (args->csa_sequenceid == slot->seq_nr) {
-		dprintk("%s seqid %d is a replay - no DRC available\n",
+		dprintk("%s seqid %d is a replay\n",
 			__func__, args->csa_sequenceid);
-		return htonl(NFS4_OK);
+		/* Signal process_op to set this error on next op */
+		if (args->csa_cachethis == 0)
+			return htonl(NFS4ERR_RETRY_UNCACHED_REP);
+
+		/* The ca_maxresponsesize_cached is 0 with no DRC */
+		else if (args->csa_cachethis == 1)
+			return htonl(NFS4ERR_REP_TOO_BIG_TO_CACHE);
 	}
 
 	/* Wraparound */
@@ -319,9 +324,13 @@ out:
 		kfree(args->csa_rclists[i].rcl_refcalls);
 	kfree(args->csa_rclists);
 
-	dprintk("%s: exit with status = %d\n", __func__, ntohl(status));
+	if (status == htonl(NFS4ERR_RETRY_UNCACHED_REP))
+		res->csr_status = 0;
+	else
 		res->csr_status = status;
-	return res->csr_status;
+	dprintk("%s: exit with status = %d res->csr_status %d\n", __func__,
+		ntohl(status), ntohl(res->csr_status));
+	return status;
 }
 
 unsigned nfs4_callback_recallany(struct cb_recallanyargs *args, void *dummy)

fs/nfs/callback_xdr.c

@@ -605,7 +605,7 @@ preprocess_nfs4_op(unsigned int op_nr, struct callback_op **op)
 static __be32 process_op(uint32_t minorversion, int nop,
 		struct svc_rqst *rqstp,
 		struct xdr_stream *xdr_in, void *argp,
-		struct xdr_stream *xdr_out, void *resp)
+		struct xdr_stream *xdr_out, void *resp, int* drc_status)
 {
 	struct callback_op *op = &callback_ops[0];
 	unsigned int op_nr;
@@ -628,6 +628,11 @@ static __be32 process_op(uint32_t minorversion, int nop,
 	if (status)
 		goto encode_hdr;
 
+	if (*drc_status) {
+		status = *drc_status;
+		goto encode_hdr;
+	}
+
 	maxlen = xdr_out->end - xdr_out->p;
 	if (maxlen > 0 && maxlen < PAGE_SIZE) {
 		status = op->decode_args(rqstp, xdr_in, argp);
@@ -636,6 +641,12 @@ static __be32 process_op(uint32_t minorversion, int nop,
 	} else
 		status = htonl(NFS4ERR_RESOURCE);
 
+	/* Only set by OP_CB_SEQUENCE processing */
+	if (status == htonl(NFS4ERR_RETRY_UNCACHED_REP)) {
+		*drc_status = status;
+		status = 0;
+	}
+
 encode_hdr:
 	res = encode_op_hdr(xdr_out, op_nr, status);
 	if (unlikely(res))
@@ -655,7 +666,7 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 	struct cb_compound_hdr_res hdr_res = { NULL };
 	struct xdr_stream xdr_in, xdr_out;
 	__be32 *p;
-	__be32 status;
+	__be32 status, drc_status = 0;
 	unsigned int nops = 0;
 
 	dprintk("%s: start\n", __func__);
@@ -675,8 +686,8 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 		return rpc_system_err;
 
 	while (status == 0 && nops != hdr_arg.nops) {
-		status = process_op(hdr_arg.minorversion, nops,
+		status = process_op(hdr_arg.minorversion, nops, rqstp,
-				    rqstp, &xdr_in, argp, &xdr_out, resp);
+				    &xdr_in, argp, &xdr_out, resp, &drc_status);
 		nops++;
 	}