[dm-devel] [PATCH 01/16] block: fix elevator init check

[Jens Axboe]

On Mon, Jan 23 2017, Christoph Hellwig wrote:
> We can't initalize the elevator fields for flushes as flush share space
> in struct request with the elevator data.  But currently we can't
> commnicate that a request is a flush through blk_get_request as we
> can only pass READ or WRITE, and the low-level code looks at the
> possible NULL bio to check for a flush.
> 
> Fix this by allowing to pass any block op and flags, and by checking for
> the flush flags in __get_request.

We check for REQ_PREFLUSH | REQ_FUA in so many places though, might not
be a bad idea to keep the helper but just make it take the opf and fix
up the other locations too. The fact that PREFLUSH|FUA is the magic to
check for is somewhat tribal knowledge.

-- 
Jens Axboe