NFSv4: Add encode/decode of the layoutreturn op in OPEN_DOWNGRADE

While we do not need to return the RW layout when downgrading from a
read/write open state to read-only, we might want to do so in order
to reduce the burden on the metadataserver so that it does not need
to check for changed data when responding to GETATTR requests.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs4xdr.c

@@ -502,11 +502,13 @@ static int nfs4_stat_to_errno(int);
 				(compound_encode_hdr_maxsz + \
 				 encode_sequence_maxsz + \
 				 encode_putfh_maxsz + \
+				 encode_layoutreturn_maxsz + \
 				 encode_open_downgrade_maxsz)
 #define NFS4_dec_open_downgrade_sz \
 				(compound_decode_hdr_maxsz + \
 				 decode_sequence_maxsz + \
 				 decode_putfh_maxsz + \
+				 decode_layoutreturn_maxsz + \
 				 decode_open_downgrade_maxsz)
 #define NFS4_enc_close_sz	(compound_encode_hdr_maxsz + \
 				 encode_sequence_maxsz + \
@@ -2356,6 +2358,8 @@ static void nfs4_xdr_enc_open_downgrade(struct rpc_rqst *req,
 	encode_compound_hdr(xdr, req, &hdr);
 	encode_sequence(xdr, &args->seq_args, &hdr);
 	encode_putfh(xdr, args->fh, &hdr);
+	if (args->lr_args)
+		encode_layoutreturn(xdr, args->lr_args, &hdr);
 	encode_open_downgrade(xdr, args, &hdr);
 	encode_nops(&hdr);
 }
@@ -6151,6 +6155,12 @@ static int nfs4_xdr_dec_open_downgrade(struct rpc_rqst *rqstp,
 	status = decode_putfh(xdr);
 	if (status)
 		goto out;
+	if (res->lr_res) {
+		status = decode_layoutreturn(xdr, res->lr_res);
+		res->lr_ret = status;
+		if (status)
+			goto out;
+	}
 	status = decode_open_downgrade(xdr, res);
 out:
 	return status;