linux-kernel - Re: [dm-devel] [PATCH v7 02/13] block: allow blk-zoned devices to have non-power-of-2 zone size

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Date:   Wed, 15 Jun 2022 13:28:07 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Pankaj Raghav <p.raghav@...sung.com>, hch@....de,
        snitzer@...hat.com, damien.lemoal@...nsource.wdc.com,
        axboe@...nel.dk
Cc:     pankydev8@...il.com, gost.dev@...sung.com,
        jiangbo.365@...edance.com, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        dm-devel@...hat.com, jonathan.derrick@...ux.dev,
        Johannes.Thumshirn@....com, dsterba@...e.com, jaegeuk@...nel.org,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [dm-devel] [PATCH v7 02/13] block: allow blk-zoned devices to
 have non-power-of-2 zone size

On 6/15/22 03:19, Pankaj Raghav wrote:
> @@ -489,14 +489,27 @@ static int blk_revalidate_zone_cb(struct blk_zone *zone, unsigned int idx,
>   	 * smaller last zone.
>   	 */
>   	if (zone->start == 0) {
> -		if (zone->len == 0 || !is_power_of_2(zone->len)) {
> -			pr_warn("%s: Invalid zoned device with non power of two zone size (%llu)\n",
> -				disk->disk_name, zone->len);
> +		if (zone->len == 0) {
> +			pr_warn("%s: Invalid zone size", disk->disk_name);
> +			return -ENODEV;
> +		}
> +
> +		/*
> +		 * Don't allow zoned device with non power_of_2 zone size with
> +		 * zone capacity less than zone size.
> +		 */

Please change "power_of_2" into "power-of-2".

> +		if (!is_power_of_2(zone->len) && zone->capacity < zone->len) {
> +			pr_warn("%s: Invalid zone capacity for non power of 2 zone size",
> +				disk->disk_name);
>   			return -ENODEV;
>   		}

The above check seems wrong to me. I don't see why devices that report a 
capacity that is less than the zone size should be rejected.

> +		/*
> +		 * Division is used to calculate nr_zones for both power_of_2
> +		 * and non power_of_2 zone sizes as it is not in the hot path.
> +		 */

Shouldn't the above comment be moved to the patch description? I'm not 
sure whether having such a comment in the source code is valuable.

> +static inline sector_t blk_queue_offset_from_zone_start(struct request_queue *q,
> +							sector_t sec)
> +{
> +	sector_t zone_sectors = blk_queue_zone_sectors(q);
> +	u64 remainder = 0;
> +
> +	if (!blk_queue_is_zoned(q))
> +		return false;

"return false" should only occur in functions returning a boolean. This 
function returns type sector_t.

Thanks,

Bart.