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

[Nikolay Borisov <nborisov@suse.com>]

On 13.05.22 г. 21:42 ч., Nikolay Borisov wrote:
> 
> 
> 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

... and David has already seen it so this is noop :)
> 
>>   #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);
>