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.
