On Sat, Jan 09, 2016 at 07:21:12PM -0600, Mike Christie wrote:

Oh yeah, to answer the second part of your question, REQ_OP_FLUSH is
only a flush operation like what request_fn drivers wanted.

And that's the odd part that trips me up.

REQ_PREFLUSH can be set with a REQ_OP_WRITE bio when filesystems want to
do both.

There is then the case where filesystems and blkdev_issue_flush could
just want to request a flush. I left them as a REQ_PREFLUSH with
REQ_OP_WRITE set, so there would be a single code path.

But the pure flush without data transfer case is pretty different,
so it seems rather odd to handle it like that.  But I suspec we could
just fix that up later.