Redefined the contents of OutMessage.

internal/buffer/out_message.go

@@ -21,14 +21,18 @@ import (
 	"github.com/jacobsa/fuse/internal/fusekernel"
 )
 
+// We size out messages to be large enough to hold a header for the response
+// plus the largest read that may come in.
+const outMessageSize = unsafe.Sizeof(fusekernel.OutHeader{}) + MaxReadSize
+
 // OutMessage provides a mechanism for constructing a single contiguous fuse
 // message from multiple segments, where the first segment is always a
 // fusekernel.OutHeader message.
 //
-// Must be created with NewOutMessage. Exception: the zero value has
-// Bytes() == nil.
+// Must be initialized with Reset.
 type OutMessage struct {
-	slice []byte
+	offset  uintptr
+	storage [outMessageSize]byte
 }
 
 // Create a new buffer whose initial contents are a zeroed fusekernel.OutHeader

internal/buffer/out_message_darwin.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 read size that we expect to ever see from the kernel, used for
+// calculating the size of out messages.
+//
+// Experimentally determined on OS X.
+const MaxReadSize = 1 << 20