NFSv4.1/flexfiles: Fix a protocol error in layoutreturn

According to the flexfiles protocol, the layoutreturn should specify an
array of errors in the following format:

struct ff_ioerr4 {
	offset4        ffie_offset;
	length4        ffie_length;
	stateid4       ffie_stateid;
	device_error4  ffie_errors<>;
};

This patch fixes up the code to ensure that our ffie_errors is indeed
encoded as an array (albeit with only a single entry).
Reported-by: Tom Haynes <thomas.haynes@primarydata.com>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayoutdev.c

@@ -500,16 +500,19 @@ int ff_layout_encode_ds_ioerr(struct nfs4_flexfile_layout *flo,
 					   range->offset, range->length))
 			continue;
 		/* offset(8) + length(8) + stateid(NFS4_STATEID_SIZE)
-		 * + deviceid(NFS4_DEVICEID4_SIZE) + status(4) + opnum(4)
+		 * + array length + deviceid(NFS4_DEVICEID4_SIZE)
+		 * + status(4) + opnum(4)
 		 */
 		p = xdr_reserve_space(xdr,
-				24 + NFS4_STATEID_SIZE + NFS4_DEVICEID4_SIZE);
+				28 + NFS4_STATEID_SIZE + NFS4_DEVICEID4_SIZE);
 		if (unlikely(!p))
 			return -ENOBUFS;
 		p = xdr_encode_hyper(p, err->offset);
 		p = xdr_encode_hyper(p, err->length);
 		p = xdr_encode_opaque_fixed(p, &err->stateid,
 					    NFS4_STATEID_SIZE);
+		/* Encode 1 error */
+		*p++ = cpu_to_be32(1);
 		p = xdr_encode_opaque_fixed(p, &err->deviceid,
 					    NFS4_DEVICEID4_SIZE);
 		*p++ = cpu_to_be32(err->status);