* Use direct-io mode to reduce IO.
* Add testViewHook helper to recovery the backing file since the ext4
might need writable permission to handle recovery. If the backing file
needs recovery and it's for View snapshot, the readonly mount will
cause error.
* Use 8 MiB as capacity to reduce the IO.
Signed-off-by: Wei Fu <fuweid89@gmail.com>
7de95cbc4c