linux-kernel - Re: [PATCH v6 8/8] dm: ensure only power of 2 zone sizes are allowed

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Message-ID: <9703ca4c-33cf-cb3a-b46b-6b0e5537cfd6@opensource.wdc.com>
Date:   Thu, 26 May 2022 08:13:49 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Pankaj Raghav <p.raghav@...sung.com>, axboe@...nel.dk,
        snitzer@...hat.com, Johannes.Thumshirn@....com, hch@....de,
        hare@...e.de
Cc:     dsterba@...e.com, dm-devel@...hat.com, jiangbo.365@...edance.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, jaegeuk@...nel.org,
        gost.dev@...sung.com
Subject: Re: [PATCH v6 8/8] dm: ensure only power of 2 zone sizes are allowed

On 5/26/22 00:49, Pankaj Raghav wrote:
> Ensure that only power of 2 zoned devices are enabled for dm targets that
> supports zoned devices. This constraint can be relaxed once non power of
> 2 zone size support is added to the DM layer.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  drivers/md/dm-table.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 03541cfc2317..2a8af70d1d4a 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -251,6 +251,12 @@ static int device_area_is_invalid(struct dm_target *ti, struct dm_dev *dev,
>  	if (bdev_is_zoned(bdev)) {
>  		unsigned int zone_sectors = bdev_zone_sectors(bdev);
>  
> +		if (!is_power_of_2(zone_sectors)) {
> +			DMWARN("%s: %pg only power of two zone size supported",
> +			       dm_device_name(ti->table->md), bdev);
> +			return 1;
> +		}
> +
>  		if (start & (zone_sectors - 1)) {
>  			DMWARN("%s: start=%llu not aligned to h/w zone size %u of %pg",
>  			       dm_device_name(ti->table->md),

I thought the agreed upon idea is be to add a dm-linear like target to
emulate power of 2 zone size so that we can keep btrfs and f2fs running on
this new class of device. So why this patch ?

The entire series as is will fragment zoned block device support, which is
not a good thing at all. Without the new dm target, none of the current
kernel supported zone stuff will work.

The zonefs patch is also gone from the series. Why ? As is, zonefs will
break if it is passed a non power of 2 zone size drive.

-- 
Damien Le Moal
Western Digital Research