gh-138712: Add os.NODEV (GH-138728)

Author: serhiy-storchaka

Doc/library/os.rst

@@ -2630,6 +2630,13 @@ features:
    Compose a raw device number from the major and minor device numbers.
 
 
+.. data:: NODEV
+
+   Non-existent device.
+
+   .. versionadded:: next
+
+
 .. function:: pathconf(path, name)
 
    Return system configuration information relevant to a named file. *name*

Lib/test/test_posix.py

@@ -757,12 +757,30 @@ def test_makedev(self):
             self.assertRaises((ValueError, OverflowError), posix.makedev, x, minor)
             self.assertRaises((ValueError, OverflowError), posix.makedev, major, x)
 
-        if sys.platform == 'linux' and not support.linked_to_musl():
-            NODEV = -1
+        # The following tests are needed to test functions accepting or
+        # returning the special value NODEV (if it is defined). major(), minor()
+        # and makefile() are the only easily reproducible examples, but that
+        # behavior is platform specific -- on some platforms their code has
+        # a special case for NODEV, on others this is just an implementation
+        # artifact.
+        if (hasattr(posix, 'NODEV') and
+            sys.platform.startswith(('linux', 'macos', 'freebsd', 'dragonfly',
+                                     'sunos'))):
+            NODEV = posix.NODEV
             self.assertEqual(posix.major(NODEV), NODEV)
             self.assertEqual(posix.minor(NODEV), NODEV)
             self.assertEqual(posix.makedev(NODEV, NODEV), NODEV)
 
+    def test_nodev(self):
+        # NODEV is not a part of Posix, but is defined on many systems.
+        if (not hasattr(posix, 'NODEV')
+            and (not sys.platform.startswith(('linux', 'macos', 'freebsd',
+                                              'dragonfly', 'netbsd', 'openbsd',
+                                              'sunos'))
+                 or support.linked_to_musl())):
+            self.skipTest('not defined on this platform')
+        self.assertHasAttr(posix, 'NODEV')
+
     def _test_all_chown_common(self, chown_func, first_param, stat_func):
         """Common code for chown, fchown and lchown tests."""
         def check_stat(uid, gid):

Misc/NEWS.d/next/Library/2025-09-10-10-11-59.gh-issue-138712.avrPG5.rst

@@ -0,0 +1 @@
+Add :const:`os.NODEV`.

Modules/posixmodule.c

@@ -17861,6 +17861,10 @@ all_ins(PyObject *m)
 #endif
 #endif  /* HAVE_EVENTFD && EFD_CLOEXEC */
 
+#ifdef NODEV
+    if (PyModule_Add(m, "NODEV", _PyLong_FromDev(NODEV))) return -1;
+#endif
+
 #if defined(__APPLE__)
     if (PyModule_AddIntConstant(m, "_COPYFILE_DATA", COPYFILE_DATA)) return -1;
     if (PyModule_AddIntConstant(m, "_COPYFILE_STAT", COPYFILE_STAT)) return -1;