linux-kernel - Re: [PATCH v2] block: ublk: enable zoned storage support

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Message-ID: <87h6v3l9up.fsf@metaspace.dk>
Date:   Thu, 02 Mar 2023 11:07:15 +0100
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     linux-block@...r.kernel.org, Hans Holmberg <Hans.Holmberg@....com>,
        Matias Bjorling <Matias.Bjorling@....com>,
        Niklas Cassel <Niklas.Cassel@....com>,
        kernel test robot <lkp@...el.com>,
        Jens Axboe <axboe@...nel.dk>,
        open list <linux-kernel@...r.kernel.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Subject: Re: [PATCH v2] block: ublk: enable zoned storage support


Ming Lei <ming.lei@...hat.com> writes:

> On Thu, Mar 2, 2023 at 5:02 PM Ming Lei <ming.lei@...hat.com> wrote:
>>
>> On Thu, Mar 02, 2023 at 04:32:21PM +0800, Ming Lei wrote:
>> > On Thu, Mar 02, 2023 at 08:31:07AM +0100, Andreas Hindborg wrote:
>> > >
>>
>> ...
>>
>> > >
>> > > I agree about fetching more zones. However, it is no good to fetch up to
>> > > a max, since the requested zone report may less than max. I was
>> >
>> > Short read should always be supported, so the interface may need to
>> > return how many zones in single command, please refer to nvme_ns_report_zones().
>>
>> blk_zone is part of uapi, maybe the short read can be figured out by
>> one all-zeroed 'blk_zone'?  then no extra uapi data is needed for
>> reporting zones.
>
> oops, we have blk_zone_report data for reporting zones to userspace already,
> see blkdev_report_zones_ioctl(), then this way can be re-used for getting zone
> report from ublk server too, right?

Yes that would be nice. But I did the report_zone command like a read
operation, so we are not currently copying any buffers to user space
when issuing the command, we just rely on the iod. I think it would be
better to use the start_sectors and nr_sectors of the iod instead. Then
we don't have to copy the blk_zone_report. What do you think?

BR Andreas