[PATCH V2 11/12] nvmet: use minimized version of blk_rq_append_bio

[Christoph Hellwig]

On Mon, Aug 31, 2020 at 03:27:06PM -0700, Chaitanya Kulkarni wrote:
> The function blk_rq_append_bio() is a genereric API written for all
> types driver (having bounce buffers) and different context (where
> request is already having a bio i.e. rq->bio != NULL).
> 
> It does mainly three things: calculating the segments, bounce queue and
> if req->bio == NULL call blk_rq_bio_prep() or handle low level merge()
> case.
> 
> The NVMe PCIe driver does not use the queue bounce mechanism. In order
> to find this out for each request processing in the passthru
> blk_rq_append_bio() does extra work in the fast path for each request.

We need to be able to deal with all transport drivers.  None of them
uses bounce buffering, but the changelog needs to be correct.