1 files changed, 58 insertions, 0 deletions
diff --git a/lib/diskio/ref.go b/lib/diskio/ref.go
new file mode 100644
index 0000000..fe284d7
--- /dev/null
+++ b/lib/diskio/ref.go
@@ -0,0 +1,58 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package util
+
+import (
+	"fmt"
+	"io"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
+)
+
+type File[A ~int64] interface {
+	Name() string
+	Size() (A, error)
+	ReadAt(p []byte, off A) (n int, err error)
+	WriteAt(p []byte, off A) (n int, err error)
+}
+
+var (
+	_ io.WriterAt = File[int64](nil)
+	_ io.ReaderAt = File[int64](nil)
+)
+
+type Ref[A ~int64, T any] struct {
+	File File[A]
+	Addr A
+	Data T
+}
+
+func (r *Ref[A, T]) Read() error {
+	size := binstruct.StaticSize(r.Data)
+	buf := make([]byte, size)
+	if _, err := r.File.ReadAt(buf, r.Addr); err != nil {
+		return err
+	}
+	n, err := binstruct.Unmarshal(buf, &r.Data)
+	if err != nil {
+		return err
+	}
+	if n != size {
+		return fmt.Errorf("util.Ref[%T].Read: left over data: read %v bytes but only consumed %v",
+			r.Data, size, n)
+	}
+	return nil
+}
+
+func (r *Ref[A, T]) Write() error {
+	buf, err := binstruct.Marshal(r.Data)
+	if err != nil {
+		return err
+	}
+	if _, err = r.File.WriteAt(buf, r.Addr); err != nil {
+		return err
+	}
+	return nil
+}