Re: [PATCH V4 14/24] block: add `struct elv_change_ctx` for unifying elevator change

[Christoph Hellwig <hch@lst.de>]

>  void elv_update_nr_hw_queues(struct request_queue *q)
>  {
> -	const char *name = "none";
> +	struct elv_change_ctx ctx = {
> +		.name	= "none",
> +	};
>  
>  	WARN_ON_ONCE(q->mq_freeze_depth == 0);
>  
>  	mutex_lock(&q->elevator_lock);
>  	if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q))
> -		name = q->elevator->type->elevator_name;
> +		ctx.name = q->elevator->type->elevator_name;
>  	/* force to reattach elevator after nr_hw_queue is updated */
> -	elevator_switch(q, name);
> +	elevator_switch(q, &ctx);

I don't think this elevator_switch is needed or even a good idea outside
the above if clause.  Moving it in there would also restore the behavior
in the earlier version of this series.

With that ctx.name also doesn't need to be initialized to none at
declaration time.