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/rpc-client-interface.go

@@ -0,0 +1,59 @@
+/*
+ * 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
+
+// LockArgs is minimal required values for any dsync compatible lock operation.
+type LockArgs struct {
+	// Unique ID of lock/unlock request.
+	UID string
+
+	// Resource contains a entity to be locked/unlocked.
+	Resource string
+
+	// Source contains the line number, function and file name of the code
+	// on the client node that requested the lock.
+	Source string
+}
+
+// NetLocker is dsync compatible locker interface.
+type NetLocker interface {
+	// Do read lock for given LockArgs.  It should return
+	// * a boolean to indicate success/failure of the operation
+	// * an error on failure of lock request operation.
+	RLock(args LockArgs) (bool, error)
+
+	// Do write lock for given LockArgs. It should return
+	// * a boolean to indicate success/failure of the operation
+	// * an error on failure of lock request operation.
+	Lock(args LockArgs) (bool, error)
+
+	// Do read unlock for given LockArgs. It should return
+	// * a boolean to indicate success/failure of the operation
+	// * an error on failure of unlock request operation.
+	RUnlock(args LockArgs) (bool, error)
+
+	// Do write unlock for given LockArgs. It should return
+	// * a boolean to indicate success/failure of the operation
+	// * an error on failure of unlock request operation.
+	Unlock(args LockArgs) (bool, error)
+
+	// Returns underlying endpoint of this lock client instance.
+	String() string
+
+	// Close closes any underlying connection to the service endpoint
+	Close() error
+}