storage rework

pkg/cowutils/cowutils.go

@@ -0,0 +1,14 @@
+package cowutils
+
+import (
+	"errors"
+)
+
+// ErrNotSupported is returned by Always() if the operation is not
+// supported on the current operating system. Auto() will never return this
+// error.
+var (
+	ErrNotSupported = errors.New("cow is not supported on this OS")
+	ErrFailed       = errors.New("cow is not supported on this OS or file")
+	ErrTooSmall     = errors.New("file is too smaller then filesystem block size")
+)