Initial commit

vendor/github.com/cockroachdb/pebble/vfs/fd.go

@@ -0,0 +1,42 @@
+// Copyright 2021 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package vfs
+
+// fdGetter is an interface for a file with an Fd() method. A lot of
+// File related optimizations (eg. Prefetch(), WAL recycling) rely on the
+// existence of the Fd method to return a raw file descriptor.
+type fdGetter interface {
+	Fd() uintptr
+}
+
+// fdFileWrapper is a File wrapper that also exposes an Fd() method. Used to
+// wrap outer (wrapped) Files that could unintentionally hide the Fd() method
+// exposed by the inner (unwrapped) File. It effectively lets the Fd() method
+// bypass the outer File and go to the inner File.
+type fdFileWrapper struct {
+	File
+
+	// All methods usually pass through to File above, except for Fd(), which
+	// bypasses it and gets called directly on the inner file.
+	inner fdGetter
+}
+
+func (f *fdFileWrapper) Fd() uintptr {
+	return f.inner.Fd()
+}
+
+// WithFd takes an inner (unwrapped) and an outer (wrapped) vfs.File,
+// and returns an fdFileWrapper if the inner file has an Fd() method. Use this
+// method to fix the hiding of the Fd() method and the subsequent unintentional
+// disabling of Fd-related file optimizations.
+func WithFd(inner, outer File) File {
+	if f, ok := inner.(fdGetter); ok {
+		return &fdFileWrapper{
+			File:  outer,
+			inner: f,
+		}
+	}
+	return outer
+}