Re: [PATCH v2] btrfs: zoned: introduce a minimal zone size and reject mount

[Nikolay Borisov <nborisov@suse.com>]

On 13.05.22 г. 18:52 ч., Johannes Thumshirn wrote:
> Zoned devices are expected to have zone sizes in the range of 1-2GB for
> ZNS SSDs and SMR HDDs have zone sizes of 256MB, so there is no need to
> allow arbitrarily small zone sizes on btrfs.
> 
> But for testing purposes with emulated devices it is sometimes desirable
> to create devices with as small as 4MB zone size to uncover errors.
> 
> So use 4MB as the smallest possible zone size and reject mounts of devices
> with a smaller zone size.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>   fs/btrfs/zoned.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 1b1b310c3c51..d9579d4ec0f2 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -51,11 +51,13 @@
>   #define BTRFS_MIN_ACTIVE_ZONES		(BTRFS_SUPER_MIRROR_MAX + 5)
>   
>   /*
> - * Maximum supported zone size. Currently, SMR disks have a zone size of
> - * 256MiB, and we are expecting ZNS drives to be in the 1-4GiB range. We do not
> - * expect the zone size to become larger than 8GiB in the near future.
> + * Minimum / maximum supported zone size. Currently, SMR disks have a zone
> + * size of 256MiB, and we are expecting ZNS drives to be in the 1-4GiB range.
> + * We do not expect the zone size to become larger than 8GiB or smaller than
> + * 4MiB in the near future.
>    */
>   #define BTRFS_MAX_ZONE_SIZE		SZ_8G
> +#define BTRFS_MIN_ZONE_SIZE		(4 * SZ_1M)

nit: we already have SZ_4M

>   
>   #define SUPER_INFO_SECTORS	((u64)BTRFS_SUPER_INFO_SIZE >> SECTOR_SHIFT)
>   
> @@ -402,6 +404,13 @@ int btrfs_get_dev_zone_info(struct btrfs_device *device, bool populate_cache)
>   				 zone_info->zone_size, BTRFS_MAX_ZONE_SIZE);
>   		ret = -EINVAL;
>   		goto out;
> +	} else if (zone_info->zone_size < BTRFS_MIN_ZONE_SIZE) {
> +		btrfs_err_in_rcu(fs_info,
> +		"zoned: %s: zone size %llu smaller than supported minimum %u",
> +				 rcu_str_deref(device->name),
> +				 zone_info->zone_size, BTRFS_MIN_ZONE_SIZE);
> +		ret = -EINVAL;
> +		goto out;
>   	}
>   
>   	nr_sectors = bdev_nr_sectors(bdev);