o Divyesh had gotten rid of this code in the past. I want to re-introduce it
  back as it helps me a lot during debugging.
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Reviewed-by: NDivyesh Shah <dpshah@google.com>
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>