filer: cross cluster synchronization

other/java/client/src/main/proto/filer.proto

@@ -58,6 +58,12 @@ service SeaweedFiler {
     rpc LocateBroker (LocateBrokerRequest) returns (LocateBrokerResponse) {
     }
 
+    rpc KvGet (KvGetRequest) returns (KvGetResponse) {
+    }
+
+    rpc KvPut (KvPutRequest) returns (KvPutResponse) {
+    }
+
 }
 
 //////////////////////////////////////////////////
@@ -308,3 +314,19 @@ message LocateBrokerResponse {
     }
     repeated Resource resources = 2;
 }
+
+// Key-Value operations
+message KvGetRequest {
+    bytes key = 1;
+}
+message KvGetResponse {
+    bytes value = 1;
+    string error = 2;
+}
+message KvPutRequest {
+    bytes key = 1;
+    bytes value = 2;
+}
+message KvPutResponse {
+    string error = 1;
+}