Issue #8876: distutils now falls back to copying files when hard linking doesn't work.

This allows use with special filesystems such as VirtualBox shared folders.

Lib/distutils/file_util.py

@@ -80,7 +80,8 @@ def copy_file(src, dst, preserve_mode=1, preserve_times=1, update=0,
     (os.symlink) instead of copying: set it to "hard" or "sym"; if it is
     None (the default), files are copied.  Don't set 'link' on systems that
     don't support it: 'copy_file()' doesn't check if hard or symbolic
-    linking is available.
+    linking is available. If hardlink fails, falls back to
+    _copy_file_contents().
 
     Under Mac OS, uses the native file copy function in macostools; on
     other systems, uses '_copy_file_contents()' to copy file contents.
@@ -132,14 +133,21 @@ def copy_file(src, dst, preserve_mode=1, preserve_times=1, update=0,
     # (Unix only, of course, but that's the caller's responsibility)
     elif link == 'hard':
         if not (os.path.exists(dst) and os.path.samefile(src, dst)):
+            try:
                 os.link(src, dst)
+                return (dst, 1)
+            except OSError:
+                # If hard linking fails, fall back on copying file
+                # (some special filesystems don't support hard linking
+                #  even under Unix, see issue #8876).
+                pass
     elif link == 'sym':
         if not (os.path.exists(dst) and os.path.samefile(src, dst)):
             os.symlink(src, dst)
+            return (dst, 1)
 
     # Otherwise (non-Mac, not linking), copy the file contents and
     # (optionally) copy the times and mode.
-    else:
     _copy_file_contents(src, dst)
     if preserve_mode or preserve_times:
         st = os.stat(src)

Lib/distutils/tests/test_file_util.py

@@ -5,7 +5,7 @@ import shutil
 import errno
 from unittest.mock import patch
 
-from distutils.file_util import move_file
+from distutils.file_util import move_file, copy_file
 from distutils import log
 from distutils.tests import support
 from distutils.errors import DistutilsFileError
@@ -78,6 +78,36 @@ class FileUtilTestCase(support.TempdirManager, unittest.TestCase):
                 fobj.write('spam eggs')
             move_file(self.source, self.target, verbose=0)
 
+    def test_copy_file_hard_link(self):
+        with open(self.source, 'w') as f:
+            f.write('some content')
+        st = os.stat(self.source)
+        copy_file(self.source, self.target, link='hard')
+        st2 = os.stat(self.source)
+        st3 = os.stat(self.target)
+        self.assertTrue(os.path.samestat(st, st2), (st, st2))
+        self.assertTrue(os.path.samestat(st2, st3), (st2, st3))
+        with open(self.source, 'r') as f:
+            self.assertEqual(f.read(), 'some content')
+
+    def test_copy_file_hard_link_failure(self):
+        # If hard linking fails, copy_file() falls back on copying file
+        # (some special filesystems don't support hard linking even under
+        #  Unix, see issue #8876).
+        with open(self.source, 'w') as f:
+            f.write('some content')
+        st = os.stat(self.source)
+        with patch("os.link", side_effect=OSError(0, "linking unsupported")):
+            copy_file(self.source, self.target, link='hard')
+        st2 = os.stat(self.source)
+        st3 = os.stat(self.target)
+        self.assertTrue(os.path.samestat(st, st2), (st, st2))
+        self.assertFalse(os.path.samestat(st2, st3), (st2, st3))
+        for fn in (self.source, self.target):
+            with open(fn, 'r') as f:
+                self.assertEqual(f.read(), 'some content')
+
+
 def test_suite():
     return unittest.makeSuite(FileUtilTestCase)
 

Misc/NEWS

@@ -33,6 +33,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #8876: distutils now falls back to copying files when hard linking
+  doesn't work.  This allows use with special filesystems such as VirtualBox
+  shared folders.
+
 - Issue #18853: Fixed ResourceWarning in shlex.__nain__.
 
 - Issue #9351: Defaults set with set_defaults on an argparse subparser