While reviewing a Python implementation of io.FileIO (_pyio.FileIO) in the issue#21859, many issues were found in the C implementation. I open an issue to fix them.We may fix them before or after the Python implementation is merged.

fileio_drop_dup_fstat.patch: Remove the duplicate call to fstat() in fileio.c. Tests pass, invalid FD are still detected since there is a second call to fstat() which also raises OSError(EBADF) if fstat(fd) fails.

The previous change related to fstat() is the changeset3b5279b5bfd1 from the issue#21679. The changeset introduces the private _blksize attribute. The strange thing is that the changelog is:"Issue#21679: Prevent extraneous fstat() calls during open().  Patch by Bohuslav Kabrda."fstat() was called twice and it is still called twice. Maybe I missed something.

See also issue#21861: "io class name are hardcoded in reprs".In my review of _pyio.FileIO, I asked if it would be possible to use __qualname__ in __getstate__().

New changesetbc2a22eaa0af by Victor Stinner in branch 'default':Issue#23752: When built from an existing file descriptor, io.FileIO() now onlyhttps://hg.python.org/cpython/rev/bc2a22eaa0af

Hum, _Py_fstat() is not used correctly in _io.FilIO: it uses errno instead of GetLastError() to raise the OSError. It's too hard to use the new _Py_fstat() function directly, I modified it to raise directly the exception. So the caller doesn't have to use #ifdef MS_WINDOWS to raise the exception correctly.I added _Py_fstat_noraise() when it's not possible to use an exception.http://buildbot.python.org/all/builders/AMD64%20Windows7%20SP1%203.x/builds/5978/steps/test/logs/stdio======================================================================FAIL: test_fdopen (test.test_os.TestInvalidFD)----------------------------------------------------------------------Traceback (most recent call last):  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_os.py", line 1418, in check    f(support.make_bad_fd(), *args)  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\os.py", line 1028, in fdopen    return io.open(fd, *args, **kwargs)OSError: [Errno 0] ErrorDuring handling of the above exception, another exception occurred:Traceback (most recent call last):  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_os.py", line 1411, in helper    self.check(getattr(os, f))  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_os.py", line 1420, in check    self.assertEqual(e.errno, errno.EBADF)AssertionError: 0 != 9

New changeset128f92ae8bae by Victor Stinner in branch 'default':Issue#23752: _Py_fstat() is now responsible to raise the Python exceptionhttps://hg.python.org/cpython/rev/128f92ae8bae

The changeset128f92ae8bae also changed _Py_fstat() to release the GIL when calling fstat(), I forgot to mention it in the changeset.test_socket now hangs on AMD64 Snow Leop 3.x, I don't know yet if it's related:http://buildbot.python.org/all/builders/AMD64%20Snow%20Leop%203.x/builds/2870/steps/test/logs/stdio[393/393] test_socketTimeout (1:00:00)!Thread 0x0000000104fef000 (most recent call first):  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/socket.py", line 288 in _sendfile_use_sendfile  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_socket.py", line 5131 in _testOffset  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_socket.py", line 278 in clientRunThread 0x00007fff71296cc0 (most recent call first):  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/threading.py", line 293 in wait  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/threading.py", line 556 in wait  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_socket.py", line 262 in _tearDown  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 580 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 625 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 122 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 84 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 122 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 84 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/runner.py", line 176 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/support/__init__.py", line 1773 in _run_suite  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/support/__init__.py", line 1807 in run_unittest  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_socket.py", line 5340 in test_main  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 1280 in runtest_inner

Oh, there was another hang before, so it's probably not related:http://buildbot.python.org/all/builders/AMD64%20Snow%20Leop%203.x/builds/2852/steps/test/logs/stdio[393/393] test_sslTimeout (1:00:00)!Thread 0x0000000102d81000 (most recent call first):  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_ssl.py", line 2832 in serve  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/threading.py", line 871 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/threading.py", line 923 in _bootstrap_inner  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/threading.py", line 891 in _bootstrapThread 0x00007fff71296cc0 (most recent call first):  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/ssl.py", line 628 in do_handshake  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/ssl.py", line 983 in do_handshake  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/ssl.py", line 747 in __init__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/ssl.py", line 1064 in wrap_socket  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 162 in handle  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 1238 in assertRaisesRegex  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_ssl.py", line 2851 in test_handshake_timeout  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 577 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 625 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 122 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 84 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 122 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 84 in __call__  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/runner.py", line 176 in run  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/support/__init__.py", line 1773 in _run_suite

Buildbot issues were unrelated and have been fixed. I close the issue.