Re: [PATCH 2/2] block: fix the length of a smaller last zone in blkdev_get_zone_info()

[shashank Jain]

On Mon, Oct 12, 2026, Damien Le Moal wrote:
> How do you plan to issue a BLK_ZONE_REP_CACHED report? "blkzone report"
> does not have that yet. I am planning to send a patch for it.

Good point. Two options, and I am happy to follow your preference:

- Use "blkzone report" with the cached flag once your util-linux patch
  lands - that matches the existing zbd tests and avoids a bundled tool.
  I would hold the blktests submission until it is available.
- Or carry a small C helper in the blktests src/ directory that issues
  BLKREPORTZONEV2 with BLK_ZONE_REP_CACHED directly, so the test is
  self-contained and does not depend on the util-linux version.

I lean towards the first, to match the zbd conventions and your blkzone
work; tell me which you prefer and I will align the test with it.

Thanks,
Shashank

On Mon, Oct 12, 2026 at 6:07 PM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
>
> On 2026/10/12 14:29, shashank Jain wrote:
> > On Mon, Oct 12, 2026, Christoph Hellwig wrote:
> >> Can you add this to blktests as a reproducer?
> >
> > Will do. I'll send a blktests test under tests/zbd/ that sets up a zoned
> > null_blk device with a smaller last zone and checks that BLKREPORTZONEV2
> > without BLK_ZONE_REP_CACHED matches BLKREPORTZONE, and that the cached
> > report's last-zone length does not extend past the device. I'll post it
> > to the blktests project separately and reference this series.
>
> How do you plan to issue a BLK_ZONE_REP_CACHED report? "blkzone report" does not
> have that yet. I am planning to send a patch for it.
>
> >
> > Thanks,
> > Shashank
> >
> > On Mon, Oct 12, 2026 at 5:51 PM Christoph Hellwig <hch@xxxxxx> wrote:
> >>
> >> On Sun, Oct 11, 2026 at 10:49:06AM +0530, Shashank Mohan Jain wrote:
> >>> blkdev_get_zone_info() sets the length of every zone to the zone size
> >>> of the device. The last zone of a zoned block device may be smaller
> >>> than the others: blk_revalidate_zone_cb() accepts that and remembers
> >>> the capacity of that zone in disk->last_zone_capacity. For such a zone
> >>> the length reported from the cached information is too large, and
> >>> start + len is beyond the end of the device. A conventional last zone
> >>> is also given the capacity of a full zone.
> >>>
> >>> Example with a zoned null_blk device of 10 MiB (20480 sectors) with
> >>> 4 MiB zones, last zone:
> >>>
> >>>   BLKREPORTZONE:       start 16384 len 4096 capacity 4096
> >>>   BLKREPORTZONEV2 with
> >>>   BLK_ZONE_REP_CACHED: start 16384 len 8192 capacity 4096
> >>
> >> Can you add this to blktests as a reproducer?
> >>
> >> The patch looks good:
> >>
> >>
> >> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>
>
> --
> Damien Le Moal
> Western Digital Research