Allow to use "zero-copy" writes

connection.go

@@ -485,8 +485,15 @@ func (c *Connection) Reply(ctx context.Context, opErr error) {
 	outMsg := state.outMsg
 	fuseID := inMsg.Header().Unique
 
+	suppressReuse := false
+	if wr, ok := op.(*fuseops.WriteFileOp); ok {
+		suppressReuse = wr.SuppressReuse
+	}
+
 	// Make sure we destroy the messages when we're done.
-	defer c.putInMessage(inMsg)
+	if !suppressReuse {
+		defer c.putInMessage(inMsg)
+	}
 	defer c.putOutMessage(outMsg)
 
 	// Clean up state for this op.

fuseops/ops.go

@@ -744,7 +744,18 @@ type WriteFileOp struct {
 	// be written, except on error (http://goo.gl/KUpwwn). This appears to be
 	// because it uses file mmapping machinery (http://goo.gl/SGxnaN) to write a
 	// page at a time.
-	Data      []byte
+	Data []byte
+
+	// Set by the file system: "no reuse" flag.
+	//
+	// By default, the Data buffer is reused by the library, so the file system
+	// must copy the data if it wants to use it later.
+	//
+	// However, if the file system sets this flag to true, the library doesn't
+	// reuse this buffer, so the file system can safely store and use Data slice
+	// without copying memory.
+	SuppressReuse bool
+
 	OpContext OpContext
 }
 

internal/buffer/in_message_linux.go

@@ -17,4 +17,4 @@ package buffer
 // The maximum fuse write request size that InMessage can acommodate.
 //
 // As of kernel 4.20 Linux accepts writes up to 256 pages or 1MiB
-const MaxWriteSize = 1 << 20
+const MaxWriteSize = 1 << 17