# Re: \[PATCH v4 5/8\] block: introduce zone\_write\_granularity limit

- From: Martin K. Petersen \<hidden\>
- Date: 2021-02-05 02:57:53 
- List: linux-block
- Page: https://ratatoskr.run/linux-block/2021/02/6400824
- Thread: https://ratatoskr.run/linux-block/2021/02/6400824/t.md

```text

Damien,

> Per ZBC and ZAC specifications, host-managed SMR hard-disks mandate that
> all writes into sequential write required zones be aligned to the device
> physical block size. However, NVMe ZNS does not have this constraint and
> allows write operations into sequential zones to be aligned to the
> device logical block size. This inconsistency does not help with
> software portability across device types.
>
> To solve this, introduce the zone_write_granularity queue limit to
> indicate the alignment constraint, in bytes, of write operations into
> zones of a zoned block device. This new limit is exported as a
> read-only sysfs queue attribute and the helper
> blk_queue_zone_write_granularity() introduced for drivers to set this
> limit.
>
> The function blk_queue_set_zoned() is modified to set this new limit to
> the device logical block size by default. NVMe ZNS devices as well as
> zoned nullb devices use this default value as is. The scsi disk driver
> is modified to execute the blk_queue_zone_write_granularity() helper to
> set the zone write granularity of host-managed SMR disks to the disk
> physical block size.
>
> The accessor functions queue_zone_write_granularity() and
> bdev_zone_write_granularity() are also introduced.

Looks fine.

Reviewed-by: Martin K. Petersen <redacted>

-- 
Martin K. Petersen	Oracle Linux Engineering
```