Fix size exceed of dd action when clearing a volume

This patch closes a bug that may result in "No space left" error
of dd command.

If user set the config item volume_clear_size to larger value than
a size of a volume, the "dd" command will get "No space left"
error when deleting the volume.
This change rejects volume_clear_size settings that are larger
than 1GiB, because there isn't really a reason to set that.
That would be safer all-around.

DocImpact

Closes-Bug: #1588310
Change-Id: I690d62bc728c85c9795a87f84b52f1a14474933d

cinder/volume/driver.py

@@ -83,7 +83,9 @@ volume_opts = [
                help='Method used to wipe old volumes'),
     cfg.IntOpt('volume_clear_size',
                default=0,
-               help='Size in MiB to wipe at start of old volumes. 0 => all'),
+               max=1024,
+               help='Size in MiB to wipe at start of old volumes. 1024 MiB'
+                    'at max. 0 => all'),
     cfg.StrOpt('volume_clear_ionice',
                help='The flag to pass to ionice to alter the i/o priority '
                     'of the process used to zero a volume after deletion, '

releasenotes/notes/reject-volume_clear_size-settings-larger-than-1024MiB-30b38811da048948.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - Fix 'No Space left' of dd command when users set the config item
+    volume_clear_size to larger value than a size of a volume.