[PATCH v2 11/15] block: introduce BLKREPORTZONESV2 ioctl

[Damien Le Moal]

On 11/4/25 16:23, Johannes Thumshirn wrote:
> On 11/4/25 1:15 AM, Damien Le Moal wrote:
>> On 11/4/25 00:17, Johannes Thumshirn wrote:
>>> On 11/3/25 2:38 PM, Damien Le Moal wrote:
>>>> Introduce the new BLKREPORTZONESV2 ioctl command to allow user
>>>> applications access to the fast zone report implemented by
>>>> blkdev_report_zones_cached(). This new ioctl is defined as number 142
>>>> and is documented in include/uapi/linux/fs.h.
>>>>
>>>> Unlike the existing BLKREPORTZONES ioctl, this new ioctl uses the flags
>>>> field of struct blk_zone_report also as an input. If the user sets the
>>>> BLK_ZONE_REP_CACHED flag as an input, then blkdev_report_zones_cached()
>>>> is used to generate the zone report using cached zone information. If
>>>> this flag is not set, then BLKREPORTZONESV2 behaves in the same manner
>>>> as BLKREPORTZONES and the zone report is generated by accessing the
>>>> zoned device.
>>>
>>> Is there a downside to always do the caching? A.k.a do we need the new
>>> ioctl or can we keep using the old one and cache the report zones reply?
>> The old one is needed to allow getting the precise imp open, exp open, closed
>> conditions, if the user cares about these. E.g. Zonefs does because of the
>> (optional) explicit zone open done on file open.
>>
>> And we cannot break existing user space anyway (e.g. sysutils blkzone), so we
>> must return the "legacy" report unless asked otherwise.
> 
> 
> OK, let me read the patches again, but why can't we do a "write-through" 
> style caching? I.e. something in the system is executing
> 
> blkdev_report_zones(), the cache will be populated as well.

The cache is initialized with zone revalidation and maintained as IOs and zone
management operations are executeds. No need to involve blkdev_report_zones()
for maintaining the zone information. Not to mention that it would be impossible
to correctly do it without guaranteeing that report zones is the *only* command
being executed. Otherwise, by the time you process a zone report,
write/reset/finish IOs to that zone may already have changed it.

-- 
Damien Le Moal
Western Digital Research