Re: new scrub code vs zoned file systems

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2023/6/1 15:27, Christoph Hellwig wrote:
> On Thu, Jun 01, 2023 at 03:21:22PM +0800, Qu Wenruo wrote:
>> Is there any function that I can go to grab the current writer pointer?
>
> You can get the information using blkdev_report_zones, or the
> "blkzoned report" command from user space.
>
Several new bugs exposed.

- We need to forward the sctx->write_pointer after the write bio
   finished

- Wrong physical bytenr passed to fill_writer_pointer_gap()
   The 2nd one called in scrub_write_sectors() is passing logical
   address, which is definitely a big NONO.

- Missing gaps for certain bitmap layout
   If we have the following layout for write,

   0     4     8     12    16
   |     |/////|     |/////|

   We should:
   * Fill gap for [0, 4)
   * Submit write for [4, 8)
   * Fill gap for [8, 12)
   * Submit write for [12, 16)

   But we have a wrong check, we only file the gap request before
   submitting the write bio.

   This results:
   * Fill gap for [0, 12)
   * Submit write for [4, 8)
     Obvious the write would fail.
   * Fill gap for [8, 12)
     No op, because the write pointer is already at 12.
   * Submit write for [12, 16)
     Weirdly, this would not fail, as the write pointer is at 12.

In short, the fill_writer_pointer_gap() arguments are a total mess...

I will submit a proper fix soon.

Thanks,
Qu