On 2020/5/16 20:40, Christoph Hellwig wrote:
> On Sat, May 16, 2020 at 11:54:33AM +0800, Coly Li wrote:
>> The bcache driver is bio based and NOT request based multiqueued driver,
>> if a zoned SMR hard drive is used as backing device of a bcache device,
>> calling blk_revalidate_disk_zones() for the bcache device will fail due
>> to the following check in blk_revalidate_disk_zones(),
>> 478 if (WARN_ON_ONCE(!queue_is_mq(q)))
>> 479 return -EIO;
>>
>> Now bcache is able to export the zoned information from the underlying
>> zoned SMR drives and format zonefs on top of a bcache device, the
>> resitriction that a zoned device should be multiqueued is unnecessary
>> for now.
>>
>> Although in commit ae58954d8734c ("block: don't handle bio based drivers
>> in blk_revalidate_disk_zones") it is said that bio based drivers should
>> not call blk_revalidate_disk_zones() and just manually update their own
>> q->nr_zones, but this is inaccurate. The bio based drivers also need to
>> set their zone size and initialize bitmaps for cnv and seq zones, it is
>> necessary to call blk_revalidate_disk_zones() for bio based drivers.
>
> Why would you need these bitmaps for bcache? There is no reason to
> serialize requests for stacking drivers, and you can already derive
> if a zone is sequential or not from whatever internal information
> you use.
>
> So without a user that actually makes sense: NAK.
>
It is OK for me to set the zone_nr and zone size without calling
blk_revalidate_disk_zones().
Coly Li
