linux-kernel - Re: [PATCH v2] nvme: report write pointer for a full zone as zone start + zone len

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Date:   Fri, 3 Dec 2021 08:00:14 -0800
From:   Keith Busch <kbusch@...nel.org>
To:     Niklas Cassel <Niklas.Cassel@....com>
Cc:     Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        "damien.lemoal@...nsource.wdc.com" <damien.lemoal@...nsource.wdc.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] nvme: report write pointer for a full zone as zone
 start + zone len

On Fri, Nov 26, 2021 at 10:42:44AM +0000, Niklas Cassel wrote:
> From: Niklas Cassel <niklas.cassel@....com>
> 
> The write pointer in NVMe ZNS is invalid for a zone in zone state full.
> The same also holds true for ZAC/ZBC.
> 
> The current behavior for NVMe is to simply propagate the wp reported by
> the drive, even for full zones. Since the wp is invalid for a full zone,
> the wp reported by the drive may be any value.
> 
> The way that the sd_zbc driver handles a full zone is to always report
> the wp as zone start + zone len, regardless of what the drive reported.
> null_blk also follows this convention.
> 
> Do the same for NVMe, so that a BLKREPORTZONE ioctl reports the write
> pointer for a full zone in a consistent way, regardless of the interface
> of the underlying zoned block device.
> 
> blkzone report before patch:
> start: 0x000040000, len 0x040000, cap 0x03e000, wptr 0xfffffffffffbfff8
> reset:0 non-seq:0, zcond:14(fu) [type: 2(SEQ_WRITE_REQUIRED)]
> 
> blkzone report after patch:
> start: 0x000040000, len 0x040000, cap 0x03e000, wptr 0x040000 reset:0
> non-seq:0, zcond:14(fu) [type: 2(SEQ_WRITE_REQUIRED)]

Looks good.

Reviewed-by: Keith Busch <kbusch@...nel.org>