Re: split scsi passthrough fields out of struct request V2

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Feb 02 2017 at  7:20pm -0500,
Bart Van Assche <Bart.VanAssche@sandisk.com> wrote:

> On Thu, 2017-02-02 at 16:10 -0500, Mike Snitzer wrote:
> > Care to try moving the dm_get(md) at the end of dm_start_request() to
> > the beginning of dm_start_request() and report back on whether it helps
> > at all?
> 
> Hello Mike,
> 
> Sorry but I don't see how that could make a difference.

Yeah, I thought about it further after I suggested it and agree that it
shouldn't make a difference (request isn't actually issued during
dm_start_request).

> While we are at it:
> since dm_start_request() calls dm_get() and since rq_completed() calls
> dm_put(), calls to these two functions should always be paired. There is
> only one dm_start_request() call in the dm-mq code, namely the one in
> dm_mq_queue_rq(). However, if map_request() returns DM_MAPIO_REQUEUE then
> rq_completed() is called twice: a first time by
> dm_requeue_original_request() and a second time by the dm_mq_queue_rq().
> Do you agree with this?

Not seeing it.

DM_MAPIO_DELAY_REQUEUE will call dm_requeue_original_request(), but
dm_mq_queue_rq() won't call rq_completed() in that case.

And for DM_MAPIO_REQUEUE dm_mq_queue_rq() will call rq_completed().