From 5e363eb194e3d33e9a71b7f2f900e5c6dc13a0b1 Mon Sep 17 00:00:00 2001
From: Sheel Rana <ranasheel2000@gmail.com>
Date: Tue, 12 Jan 2016 01:36:46 +0530
Subject: [PATCH] Handling Invalid argument iflag=direct in dd

During volume/snapshot create/delete operations,
dd command is used to clear contents of disk.

Before invoking dd, it is checked if iflag=direct
supports dd or not by executing dd command with
iflag=direct and if=/dev/zero combination.
But this always results in invalid argument
error.

Handling for this argument is done to eliminate
unnecessary call to dd command when it is used
with iflag=direct and if=/dev/zero combination
to check if this argument supports dd or not.

Closes-Bug: #1270362

Change-Id: Ic6dd029ca1a339076e491c38ef3c69315497f189
---
 cinder/tests/unit/test_volume_utils.py | 21 +++++++++++++++++++++
 cinder/volume/utils.py                 | 12 +++++++++---
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/cinder/tests/unit/test_volume_utils.py b/cinder/tests/unit/test_volume_utils.py
index d5158dbc2..f425ea773 100644
--- a/cinder/tests/unit/test_volume_utils.py
+++ b/cinder/tests/unit/test_volume_utils.py
@@ -445,6 +445,20 @@ class OdirectSupportTestCase(test.TestCase):
         mock_exec.assert_called_once_with('dd', 'count=0', 'if=/dev/abc',
                                           'of=/dev/def', 'iflag=direct',
                                           run_as_root=True)
+        mock_exec.reset_mock()
+
+        output = volume_utils.check_for_odirect_support('/dev/zero',
+                                                        '/dev/def',
+                                                        'iflag=direct')
+        self.assertFalse(output)
+        mock_exec.reset_mock()
+
+        output = volume_utils.check_for_odirect_support('/dev/zero',
+                                                        '/dev/def')
+        self.assertTrue(output)
+        mock_exec.assert_called_once_with('dd', 'count=0', 'if=/dev/zero',
+                                          'of=/dev/def', 'oflag=direct',
+                                          run_as_root=True)
 
     @mock.patch('cinder.utils.execute',
                 side_effect=processutils.ProcessExecutionError)
@@ -454,6 +468,13 @@ class OdirectSupportTestCase(test.TestCase):
         mock_exec.assert_called_once_with('dd', 'count=0', 'if=/dev/abc',
                                           'of=/dev/def', 'oflag=direct',
                                           run_as_root=True)
+        mock_exec.reset_mock()
+        output = volume_utils.check_for_odirect_support('/dev/zero',
+                                                        '/dev/def')
+        self.assertFalse(output)
+        mock_exec.assert_called_once_with('dd', 'count=0', 'if=/dev/zero',
+                                          'of=/dev/def', 'oflag=direct',
+                                          run_as_root=True)
 
 
 class ClearVolumeTestCase(test.TestCase):
diff --git a/cinder/volume/utils.py b/cinder/volume/utils.py
index e875f5eee..f93c17c37 100644
--- a/cinder/volume/utils.py
+++ b/cinder/volume/utils.py
@@ -299,9 +299,15 @@ def check_for_odirect_support(src, dest, flag='oflag=direct'):
 
     # Check whether O_DIRECT is supported
     try:
-        utils.execute('dd', 'count=0', 'if=%s' % src, 'of=%s' % dest,
-                      flag, run_as_root=True)
-        return True
+        # iflag=direct and if=/dev/zero combination does not work
+        # error: dd: failed to open '/dev/zero': Invalid argument
+        if (src == '/dev/zero' and flag == 'iflag=direct'):
+            return False
+        else:
+            utils.execute('dd', 'count=0', 'if=%s' % src,
+                          'of=%s' % dest,
+                          flag, run_as_root=True)
+            return True
     except processutils.ProcessExecutionError:
         return False
 
-- 
2.45.2