feat: Add placeholder ReflinkCopy FileCopyMethod

Author: eth-p

copy_methods_x.go

@@ -0,0 +1,24 @@
+//go:build !darwin
+
+package copy
+
+import (
+	"os"
+)
+
+// ReflinkCopy tries to copy the file by creating a reflink from the source
+// file to the destination file. This asks the filesystem to share the
+// contents between the files using a copy-on-write method.
+//
+// Reflinks are the fastest way to copy large files, but have a few limitations:
+//
+//   - Requires using a supported filesystem (btrfs, xfs, apfs)
+//   - Source and destination must be on the same filesystem.
+//
+// See: https://btrfs.readthedocs.io/en/latest/Reflink.html
+var ReflinkCopy = FileCopyMethod{
+	fcopy: func(src, dest string, info os.FileInfo, opt Options) (err error) {
+		// Not supported os.
+		return ErrUnsupportedCopyMethod
+	},
+}

options.go

@@ -32,6 +32,7 @@ type Options struct {
 	//
 	// Available implementations:
 	//    - CopyBytes (best compatibility)
+	//    - ReflinkCopy (best performance)
 	//
 	// Some implementations may not be supported on the target GOOS, or on
 	// the user's filesystem. When these fail, an error will be returned.