Defined the constant for Linux, too.

internal/buffer/in_message_darwin.go

@@ -16,5 +16,6 @@ package buffer
 
 // The maximum fuse write request size that InMessage can acommodate.
 //
-// Experimentally, OS X appears to cap the size of writes to 1 MiB.
+// Experimentally, OS X appears to cap the size of writes to 1 MiB, regardless
+// of whether a larger size is specified in the mount options.
 const MaxWriteSize = 1 << 20

internal/buffer/in_message_linux.go

@@ -0,0 +1,21 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// 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 buffer
+
+// The maximum fuse write request size that InMessage can acommodate.
+//
+// Experimentally, Linux appears to refuse to honor a MaxWrite setting in an
+// INIT response of more than 128 KiB.
+const MaxWriteSize = 1 << 17