bpo-38030: Fix os.stat failures on block devices on Windows (GH-15681)

(cherry picked from commit 772ec0f)

Co-authored-by: Steve Dower <steve.dower@python.org>

Lib/test/test_os.py

@@ -591,6 +591,14 @@ def test_access_denied(self):
         result = os.stat(fname)
         self.assertNotEqual(result.st_size, 0)
 
+    @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+    def test_stat_block_device(self):
+        # bpo-38030: os.stat fails for block devices
+        # Test a filename like "//./C:"
+        fname = "//./" + os.path.splitdrive(os.getcwd())[0]
+        result = os.stat(fname)
+        self.assertEqual(result.st_mode, stat.S_IFBLK)
+
 
 class UtimeTests(unittest.TestCase):
     def setUp(self):

Misc/NEWS.d/next/Windows/2019-09-04-14-01-08.bpo-38030._USdtk.rst

@@ -0,0 +1 @@
+Fixes :func:`os.stat` failing for block devices on Windows

Modules/posixmodule.c

@@ -1793,13 +1793,13 @@ win32_xstat_impl(const wchar_t *path, struct _Py_stat_struct *result,
             case ERROR_INVALID_PARAMETER:
             case ERROR_INVALID_FUNCTION:
             case ERROR_NOT_SUPPORTED:
-                retval = -1;
+                /* Volumes and physical disks are block devices, e.g.
+                   \\.\C: and \\.\PhysicalDrive0. */
+                memset(result, 0, sizeof(*result));
+                result->st_mode = 0x6000; /* S_IFBLK */
                 goto cleanup;
             }
-            /* Volumes and physical disks are block devices, e.g.
-               \\.\C: and \\.\PhysicalDrive0. */
-            memset(result, 0, sizeof(*result));
-            result->st_mode = 0x6000; /* S_IFBLK */
+            retval = -1;
             goto cleanup;
         }
     }
@@ -1826,7 +1826,14 @@ win32_xstat_impl(const wchar_t *path, struct _Py_stat_struct *result,
 
 cleanup:
     if (hFile != INVALID_HANDLE_VALUE) {
-        CloseHandle(hFile);
+        /* Preserve last error if we are failing */
+        error = retval ? GetLastError() : 0;
+        if (!CloseHandle(hFile)) {
+            retval = -1;
+        } else if (retval) {
+            /* Restore last error */
+            SetLastError(error);
+        }
     }
 
     return retval;