Re: [PATCH 2/3] elevator: allow name aliases

[Omar Sandoval <osandov@osandov.com>]

On Wed, Oct 25, 2017 at 12:04:46PM -0600, Jens Axboe wrote:
> Since we now lookup elevator types with the appropriate multiqueue
> capability, allow schedulers to register with an alias alongside
> the real name. This is in preparation for allowing 'mq-deadline'
> to register an alias of 'deadline' as well.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  block/elevator.c         | 22 ++++++++++++++++------
>  include/linux/elevator.h |  1 +
>  2 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/block/elevator.c b/block/elevator.c
> index b70e69f795db..dc0432e12ecf 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -83,6 +83,16 @@ bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
>  }
>  EXPORT_SYMBOL(elv_bio_merge_ok);
>  
> +static bool elevator_match(const struct elevator_type *e, const char *name)
> +{
> +	if (!strcmp(e->elevator_name, name))
> +		return true;
> +	if (e->elevator_alias && !strcmp(e->elevator_alias, name))
> +		return true;
> +
> +	return false;
> +}
> +
>  /*
>   * Return scheduler with name 'name' and with matching 'mq capability
>   */
> @@ -91,7 +101,7 @@ static struct elevator_type *elevator_find(const char *name, bool mq)
>  	struct elevator_type *e;
>  
>  	list_for_each_entry(e, &elv_list, list) {
> -		if (!strcmp(e->elevator_name, name) && !(mq ^ e->uses_mq))
> +		if (elevator_match(e, name) && !(mq ^ e->uses_mq))
>  			return e;
>  	}
>  
> @@ -922,9 +932,9 @@ int elv_register(struct elevator_type *e)
>  	spin_unlock(&elv_list_lock);
>  
>  	/* print pretty message */
> -	if (!strcmp(e->elevator_name, chosen_elevator) ||
> +	if (elevator_match(e, chosen_elevator) ||
>  			(!*chosen_elevator &&
> -			 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
> +			 elevator_match(e, CONFIG_DEFAULT_IOSCHED)))
>  				def = " (default)";
>  
>  	printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
> @@ -1077,8 +1087,7 @@ static int __elevator_change(struct request_queue *q, const char *name)
>  	if (!e)
>  		return -EINVAL;
>  
> -	if (q->elevator &&
> -	    !strcmp(elevator_name, q->elevator->type->elevator_name)) {
> +	if (q->elevator && elevator_match(q->elevator->type, elevator_name)) {
>  		elevator_put(e);
>  		return 0;
>  	}
> @@ -1126,7 +1135,8 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
>  
>  	spin_lock(&elv_list_lock);
>  	list_for_each_entry(__e, &elv_list, list) {
> -		if (elv && !strcmp(elv->elevator_name, __e->elevator_name)) {
> +		if (elv && elevator_match(elv, __e->elevator_name) &&
> +		    !(__e->uses_mq ^ (q->mq_ops != NULL))) {

Same thing here, (__e->uses_mq == (q->mq_ops != NULL)). Still confusing
but less so.

Otherwise Reviewed-by: Omar Sandoval <osandov@fb.com>