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

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Message-ID: <ZAChttVoCHsnXmvF@T590>
Date:   Thu, 2 Mar 2023 21:16:38 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Andreas Hindborg <nmi@...aspace.dk>
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>,
        ming.lei@...hat.com
Subject: Re: [PATCH v2] block: ublk: enable zoned storage support

On Thu, Mar 02, 2023 at 11:07:15AM +0100, Andreas Hindborg wrote:
> 
> 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.

What I meant is to reuse the format of blk_zone_report for returning
multiple 'blk_zone' info in single command.

The only change is that you need to allocate one bigger kernel buffer
to hold more 'blk_zone' in single report zone request.

> 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?

For IN parameter of report zone command, you still can reuse
blk_zone_report:

struct blk_zone_report {
        __u64           sector;
        __u32           nr_zones;
        __u32           flags;
};

Just by using the 1st two 64b words of iod for holding 'blk_zone_report', and
keep the iod->addr field not touched.


[1] https://lore.kernel.org/linux-block/20230301140611.163055-1-ming.lei@redhat.com/T/#md36358552d45a7d563940632d4c779a99f72916d

Thanks,
Ming