linux-kernel - Re: [PATCH v5 2/7] block: allow blk-zoned devices to have non-power-of-2 zone size

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Message-ID: <214e0c82-ce20-ba0f-77bd-21f3b83fd1f1@samsung.com>
Date:   Tue, 24 May 2022 09:10:53 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Hannes Reinecke <hare@...e.de>, <axboe@...nel.dk>, <hch@....de>,
        <snitzer@...hat.com>, <damien.lemoal@...nsource.wdc.com>,
        <Johannes.Thumshirn@....com>
CC:     <linux-nvme@...ts.infradead.org>, <dm-devel@...hat.com>,
        <dsterba@...e.com>, <jiangbo.365@...edance.com>,
        <linux-kernel@...r.kernel.org>, <gost.dev@...sung.com>,
        <linux-block@...r.kernel.org>, <jaegeuk@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v5 2/7] block: allow blk-zoned devices to have
 non-power-of-2 zone size

On 5/24/22 07:19, Hannes Reinecke wrote:

>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index c4e4c7071b7b..f5c7a41032ba 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -676,6 +676,21 @@ static inline unsigned int
>> blk_queue_zone_no(struct request_queue *q,
>>       return div64_u64(sector, zone_sectors);
>>   }
>>   +static inline bool blk_queue_is_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;
>> +
> 
> Not sure if we need this here; surely blk_queue_zone_sectors() will
> already barf, and none of the callers did this check.
> 
I totally agree with you but all the other blk_queue_* functions had
this defensive check and I didn't want to break that pattern:

static inline unsigned int blk_queue_zone_no(struct request_queue *q,
					     sector_t sector)
{
	....
	if (!blk_queue_is_zoned(q))
		return 0;
        ....
}


>> +    if (is_power_of_2(zone_sectors))
>> +        return IS_ALIGNED(sec, zone_sectors);
>> +
And, if the chunk sectors is 0, then we will do the npo2 calculation
resulting in a divide by zero even though chances of that happening is
very very low as you pointed out.
>> +    div64_u64_rem(sec, zone_sectors, &remainder);
>> +    return remainder == 0;
>> +}
>> +
>>   static inline bool blk_queue_zone_is_seq(struct request_queue *q,
>>                        sector_t sector)
>>   {
>> @@ -722,6 +737,12 @@ static inline unsigned int
>> blk_queue_zone_no(struct request_queue *q,
>>   {
>>       return 0;
>>   }
>> +
>> +static inline bool blk_queue_is_zone_start(struct request_queue *q,
>> sector_t sec)
>> +{
>> +    return false;
>> +}
>> +
>>   static inline unsigned int queue_max_open_zones(const struct
>> request_queue *q)
>>   {
>>       return 0;
> Otherwise looks good.
> 
Thanks!
> Cheers,
> 
> Hannes