diff --git a/internal/buffer/buffer.go b/internal/buffer/buffer.go
new file mode 100644
index 0000000..d2999bc
--- /dev/null
+++ b/internal/buffer/buffer.go
@@ -0,0 +1,39 @@
+package fuseshim
+
+import (
+	"unsafe"
+
+	"github.com/jacobsa/fuse/internal/fusekernel"
+)
+
+// Buffer provides a mechanism for constructing a message from multiple
+// segments.
+type Buffer []byte
+
+// alloc allocates size bytes and returns a pointer to the new
+// segment.
+func (w *Buffer) Alloc(size uintptr) unsafe.Pointer {
+	s := int(size)
+	if len(*w)+s > cap(*w) {
+		old := *w
+		*w = make([]byte, len(*w), 2*cap(*w)+s)
+		copy(*w, old)
+	}
+	l := len(*w)
+	*w = (*w)[:l+s]
+	return unsafe.Pointer(&(*w)[l])
+}
+
+// reset clears out the contents of the buffer.
+func (w *Buffer) reset() {
+	for i := range (*w)[:cap(*w)] {
+		(*w)[i] = 0
+	}
+	*w = (*w)[:0]
+}
+
+func NewBuffer(extra uintptr) (buf Buffer) {
+	const hdrSize = unsafe.Sizeof(fusekernel.OutHeader{})
+	buf = make(Buffer, hdrSize, hdrSize+extra)
+	return
+}