ulwgl_util.py: Do not use copyfile_reflink if the root and local ar…

…e not

on the same filesystem.

ULWGL/ulwgl_util.py

@@ -50,6 +50,12 @@ def force_rename(src: Path, dst: Path):  # noqa: D103
     src.rename(dst)
 
 
+def same_fs(file1: Path, file2: Path) -> bool:  # noqa: D103
+    dev1 = file1.stat().st_dev
+    dev2 = file2.stat().st_dev
+    return dev1 == dev2
+
+
 def setup_runtime(root: Path, json: Dict[str, Any]) -> None:  # noqa: D103
     # Access the 'runtime_platform' value
     runtime_platform_value: str = json["ulwgl"]["versions"]["runtime_platform"]
@@ -191,7 +197,7 @@ def _install_ulwgl(
     """
     cp: Callable[Path, Path] = None
 
-    if hasattr(os, "copy_file_range"):
+    if same_fs(root, local) and hasattr(os, "copy_file_range"):
         log.debug("CoW filesystem detected")
         cp = copyfile_reflink
     else:
@@ -255,7 +261,7 @@ def _update_ulwgl(
     """
     cp: Callable[Path, Path] = None
 
-    if hasattr(os, "copy_file_range"):
+    if same_fs(root, local) and hasattr(os, "copy_file_range"):
         log.debug("CoW filesystem detected")
         cp = copyfile_reflink
     else: