Improve check for O_TMPFILE support in unit tests

On Python < 3.4, there is no os.O_TMPFILE, so the check for O_TMPFILE
support was always reporting no-support. We now use utils.O_TMPFILE,
which is always defined.

Also, when opening an anonymous tempfile, you must open the directory
(not a file in the directory) with three flags or-ed together:
O_DIRECTORY, O_WRONLY, and O_TMPFILE. Calling open() with a subset of
those flags will receive either EISDIR or EINVAL. The check was trying
to open a file in the temp dir, so was always reporting no-support for
O_TMPFILE. We now correctly open the tempdir.

Change-Id: Iaf48ad9aecea73df4e794818dd15070360bff19f

swift/common/utils.py

@@ -4396,37 +4396,21 @@ def modify_priority(conf, logger):
 
 
 def o_tmpfile_in_path_supported(dirpath):
-    if not hasattr(os, 'O_TMPFILE'):
-        return False
-
-    testfile = os.path.join(dirpath, ".o_tmpfile.test")
-
-    hasO_TMPFILE = True
     fd = None
     try:
-        fd = os.open(testfile, os.O_CREAT | os.O_WRONLY | os.O_TMPFILE)
+        fd = os.open(dirpath, os.O_WRONLY | O_TMPFILE)
+        return True
     except OSError as e:
-        if e.errno == errno.EINVAL:
-            hasO_TMPFILE = False
+        if e.errno in (errno.EINVAL, errno.EISDIR, errno.EOPNOTSUPP):
+            return False
         else:
             raise Exception("Error on '%(path)s' while checking "
                             "O_TMPFILE: '%(ex)s'",
                             {'path': dirpath, 'ex': e})
-
-    except Exception as e:
-        raise Exception("Error on '%(path)s' while checking O_TMPFILE: "
-                        "'%(ex)s'", {'path': dirpath, 'ex': e})
-
     finally:
         if fd is not None:
             os.close(fd)
 
-        # ensure closing the fd will actually remove the file
-        if os.path.isfile(testfile):
-            return False
-
-    return hasO_TMPFILE
-
 
 def o_tmpfile_in_tmpdir_supported():
     return o_tmpfile_in_path_supported(gettempdir())