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

Nikolay Borisov
2022-05-13T18:42:56Z

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);