Re: [PATCH 1/5] null_blk: remove the bio based I/O path

[Christoph Hellwig <hch@lst.de>]

On Wed, Feb 14, 2024 at 10:25:57AM -0700, Keith Busch wrote:
> On Wed, Feb 14, 2024 at 10:54:57AM +0100, Christoph Hellwig wrote:
> > @@ -2036,11 +1813,15 @@ static int null_validate_conf(struct nullb_device *dev)
> >  		pr_err("legacy IO path is no longer available\n");
> >  		return -EINVAL;
> >  	}
> > +	if (dev->queue_mode == NULL_Q_BIO) {
> > +		pr_err("BIO-based IO path is no longer available, using blk-mq instead.\n");
> > +		dev->queue_mode = NULL_Q_MQ;
> > +	}
> 
> Seems pointless to keep dev->queue_mode around if only one value is
> valid.
> 
> Instead of checking the param here once per device, could we do it just
> once for the module in null_set_queue_mode()?

Maybe.  Note that the code would have to be quite a bit more complex
than this - not only due to configfs as noted by Damien, but also
because NULL_Q_BIO isn't rejected but simply ignored to not break
blktests.  I can look at this at parsing time, but my gut feeling
is that it's not worth the effort.