Support MinIO to be deployed on more than 32 nodes (#8492)

This PR implements locking from a global entity into
a more localized set level entity, allowing for locks
to be held only on the resources which are writing
to a collection of disks rather than a global level.

In this process this PR also removes the top-level
limit of 32 nodes to an unlimited number of nodes. This
is a precursor change before bring in bucket expansion.

pkg/dsync/dsync.go

@@ -0,0 +1,60 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package dsync
+
+import (
+	"errors"
+	"math"
+)
+
+// Dsync represents dsync client object which is initialized with
+// authenticated clients, used to initiate lock REST calls.
+type Dsync struct {
+	// Number of nodes participating in the distributed locking.
+	dNodeCount int
+
+	// List of rest client objects, one per lock server.
+	restClnts []NetLocker
+
+	// Simple majority based quorum, set to dNodeCount/2+1
+	dquorum int
+
+	// Simple quorum for read operations, set to dNodeCount/2
+	dquorumReads int
+}
+
+// New - initializes a new dsync object with input restClnts.
+func New(restClnts []NetLocker) (*Dsync, error) {
+	if len(restClnts) < 2 {
+		return nil, errors.New("Dsync is not designed for less than 2 nodes")
+	} else if len(restClnts) > 32 {
+		return nil, errors.New("Dsync is not designed for more than 32 nodes")
+	}
+
+	ds := &Dsync{}
+	ds.dNodeCount = len(restClnts)
+
+	// With odd number of nodes, write and read quorum is basically the same
+	ds.dquorum = int(ds.dNodeCount/2) + 1
+	ds.dquorumReads = int(math.Ceil(float64(ds.dNodeCount) / 2.0))
+
+	// Initialize node name and rest path for each NetLocker object.
+	ds.restClnts = make([]NetLocker, ds.dNodeCount)
+	copy(ds.restClnts, restClnts)
+
+	return ds, nil
+}