From: Pádraig Brady <pbrady@redhat.com>
Date: Wed, 16 Jan 2013 16:23:48 +0000 (+0000)
Subject: ensure zeros are written out when clearing volumes
X-Git-Url: https://review.fuel-infra.org/gitweb?a=commitdiff_plain;h=0007d255d9b20da4e5bbcdbaf5813104fbc092da;p=openstack-build%2Fcinder-build.git

ensure zeros are written out when clearing volumes

Note O_DIRECT is _not_ used when copying from /dev/zero
and there are issues with enabling that (see 444cd542).
Therefore we arrange to have dd issue an fdatasync()
to ensure the data is persisted, lest it be discarded
from the write cache when the device is unprovisioned.

* cinder/volume/drivers/lvm.py (_copy_volume): Add 'conv=fdatasync'
to the dd option list if O_DIRECT isn't used when clearing
(which it won't as descrived above).

Fixes bug: 1100363
Change-Id: I76789557754ebaeb6d52bb34548a2ef17808fbf6
---

diff --git a/cinder/volume/drivers/lvm.py b/cinder/volume/drivers/lvm.py
index b1b217d73..b3bde19b8 100644
--- a/cinder/volume/drivers/lvm.py
+++ b/cinder/volume/drivers/lvm.py
@@ -85,21 +85,27 @@ class LVMVolumeDriver(driver.VolumeDriver):
 
         self._try_execute(*cmd, run_as_root=True)
 
-    def _copy_volume(self, srcstr, deststr, size_in_g):
+    def _copy_volume(self, srcstr, deststr, size_in_g, clearing=False):
         # Use O_DIRECT to avoid thrashing the system buffer cache
-        direct_flags = ('iflag=direct', 'oflag=direct')
+        extra_flags = ['iflag=direct', 'oflag=direct']
 
         # Check whether O_DIRECT is supported
         try:
             self._execute('dd', 'count=0', 'if=%s' % srcstr, 'of=%s' % deststr,
-                          *direct_flags, run_as_root=True)
+                          *extra_flags, run_as_root=True)
         except exception.ProcessExecutionError:
-            direct_flags = ()
+            extra_flags = []
+
+        # If the volume is being unprovisioned then
+        # request the data is persisted before returning,
+        # so that it's not discarded from the cache.
+        if clearing and not extra_flags:
+            extra_flags.append('conv=fdatasync')
 
         # Perform the copy
         self._execute('dd', 'if=%s' % srcstr, 'of=%s' % deststr,
                       'count=%d' % (size_in_g * 1024), 'bs=1M',
-                      *direct_flags, run_as_root=True)
+                      *extra_flags, run_as_root=True)
 
     def _volume_not_present(self, volume_name):
         path_name = '%s/%s' % (FLAGS.volume_group, volume_name)
@@ -184,7 +190,8 @@ class LVMVolumeDriver(driver.VolumeDriver):
 
         if FLAGS.volume_clear == 'zero':
             if size_in_m == 0:
-                return self._copy_volume('/dev/zero', vol_path, size_in_g)
+                return self._copy_volume('/dev/zero', vol_path, size_in_g,
+                                         clearing=True)
             else:
                 clear_cmd = ['shred', '-n0', '-z', '-s%dMiB' % size_in_m]
         elif FLAGS.volume_clear == 'shred':