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:
> Maybe add a prep patch that defaults to BLKREPORTZONEV2 (without
> BLK_ZONE_REP_CACHED) if BLKREPORTZONEV2 is defined.
> And a second patch that adds the --cached option for BLK_ZONE_REP_CACHED.

Will do - a 2-patch series: 1/2 makes "blkzone report" use BLKREPORTZONEV2
(without BLK_ZONE_REP_CACHED) when the ioctl is defined in the headers,
keeping the current device-report behaviour; 2/2 adds "--cached" for
BLK_ZONE_REP_CACHED. I will CC you.

Thanks,
Shashank

On Mon, Oct 12, 2026 at 6:35 PM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
>
> On 2026/10/12 14:53, shashank Jain wrote:
> > On Mon, Oct 12, 2026, Damien Le Moal wrote:
> >> I was thinking on adding a "--cached" option to control the use of
> >> BLK_ZONE_REP_CACHED.
> >> If you want to take on such patch, go ahead. CC me on it and I will review.
> >
> > Thanks - yes, I will take it: a "--cached" option to "blkzone report"
> > that selects BLKREPORTZONEV2 with BLK_ZONE_REP_CACHED, leaving the
> > default report via the device (BLKREPORTZONE) unchanged. I will post it
> > to util-linux and CC you. The blktests reproducer will then use
> > "blkzone report --cached" rather than a bundled helper.
>
> Maybe add a prep patch that defaults to BLKREPORTZONEV2 (without
> BLK_ZONE_REP_CACHED) if BLKREPORTZONEV2 is defined.
>
> And a second patch that adds the --cached option for BLK_ZONE_REP_CACHED.
>
> >
> > Thanks,
> > Shashank
> >
> > On Mon, Oct 12, 2026 at 6:15 PM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> >>
> >> On 2026/10/12 14:41, shashank Jain wrote:
> >>> 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.
> >>
> >> We should leave "blkzone report" to get the device report as before, to avoid
> >> breaking anything for user with the "active" condition being returned.
> >> I was thinking on adding a "--cached" option to control the use of
> >> BLK_ZONE_REP_CACHED.
> >>
> >> If you want to take on such patch, go ahead. CC me on it and I will review. The
> >> patches I need to send to add depop support will take some more time.
> >>
> >>> - 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
> >>
> >>
> >> --
> >> Damien Le Moal
> >> Western Digital Research
>
>
> --
> Damien Le Moal
> Western Digital Research