Re: [PATCH v2 1/5] block: cleanup and export bdev IO inflight APIs

[Christoph Hellwig <hch@infradead.org>]

On Mon, Apr 21, 2025 at 09:13:57PM +0800, Yu Kuai wrote:
> > I'm not sure why this is needed or related, or even what additional
> > distinction is added here.
> 
> Because for rq-based device, there are two different stage,
> blk_account_io_start() while allocating new rq, and
> blk_mq_start_request() while issuing the rq to driver.
> 
> When will we think the reqeust is inflight? For iostat, my anser is the
> former one, because rq->start_time_ns is set here as well. And noted in
> iostats api diskstats_show（/proc/diskstats) and part_stat_show
> (/sys/block/sda/stat), inflight is get by part_in_flight, which is
> different from disk sysfs api(/sys/block/sda/inflight).

Trying to express this in a not very obvious function name isn't
going to work very well.  Documenting your findings in comments is
much better.

> > 
> > I'd just change this helper to call blk_mq_count_in_driver_rw for
> > blk-mq devices and remove the conditional from the sysfs code instead.
> > That gives us a much more robust and easier to understand API.
> 
> Ok, and another separate patch, right?

Yes.