gh-161241: Fall back when FICLONE fails with EPERM in pathlib copyfileobj

Lib/pathlib/_os.py

@@ -127,7 +127,7 @@ def copyfileobj(source_f, target_f):
                     _ficlone(source_fd, target_fd)
                     return
                 except OSError as err:
-                    if err.errno not in (EBADF, EOPNOTSUPP, ETXTBSY, EXDEV):
+                    if err.errno not in (EBADF, EOPNOTSUPP, EPERM, ETXTBSY, EXDEV):
                         raise err
 
             # Use OS copy where available.

Lib/test/test_pathlib/test_copy.py

@@ -170,5 +170,31 @@ class LocalToLocalPathCopyTest(CopyTestBase, unittest.TestCase):
         target_ground = LocalPathGround(Path)
 
 
+class CopyFileobjFallbackTest(unittest.TestCase):
+    def test_ficlone_eperm_falls_back(self):
+        # FICLONE can fail with EPERM on filesystems that block reflinks
+        # (e.g. overlayfs, or an ioctl blocked by SELinux). copyfileobj
+        # must fall back to another copy method instead of failing.
+        import errno
+        import tempfile
+        import unittest.mock
+        from pathlib import _os as pathlib_os
+
+        def failing_ficlone(source_fd, target_fd):
+            raise OSError(errno.EPERM, 'Operation not permitted')
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            source = f'{tmpdir}/source.txt'
+            target = f'{tmpdir}/target.txt'
+            with open(source, 'wb') as f:
+                f.write(b'hello world')
+            with open(source, 'rb') as source_f, open(target, 'wb') as target_f:
+                with unittest.mock.patch.object(
+                        pathlib_os, '_ficlone', failing_ficlone):
+                    pathlib_os.copyfileobj(source_f, target_f)
+            with open(target, 'rb') as f:
+                self.assertEqual(f.read(), b'hello world')
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2026-11-03-14-30-00.gh-issue-161241.abcdef.rst

@@ -0,0 +1 @@
+Fix pathlib.Path.copy failing with PermissionError when the FICLONE reflink ioctl returns EPERM; it now falls back to other copy methods.