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

[Damien Le Moal <dlemoal@kernel.org>]

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@kernel.org> 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@kernel.org> 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@lst.de> 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@lst.de>
>>>>
>>>>
>>>> --
>>>> Damien Le Moal
>>>> Western Digital Research
>>
>>
>> --
>> Damien Le Moal
>> Western Digital Research


-- 
Damien Le Moal
Western Digital Research