Re: [PATCH v10 6/9] scsi: sd_zbc: emulate ZONE_APPEND commands

From: Hannes Reinecke <hare@suse.de>
To: Johannes Thumshirn <johannes.thumshirn@wdc.com>,
	Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-block <linux-block@vger.kernel.org>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	Keith Busch <kbusch@kernel.org>,
	"linux-scsi @ vger . kernel . org" <linux-scsi@vger.kernel.org>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	"linux-fsdevel @ vger . kernel . org"
	<linux-fsdevel@vger.kernel.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v10 6/9] scsi: sd_zbc: emulate ZONE_APPEND commands
Date: Wed, 6 May 2020 20:18:04 +0200	[thread overview]
Message-ID: <f031f491-620a-6b72-f16a-3702239b01c6@suse.de> (raw)
In-Reply-To: <20200506161145.9841-7-johannes.thumshirn@wdc.com>

On 5/6/20 6:11 PM, Johannes Thumshirn wrote:
> Emulate ZONE_APPEND for SCSI disks using a regular WRITE(16) command
> with a start LBA set to the target zone write pointer position.
> 
> In order to always know the write pointer position of a sequential write
> zone, the write pointer of all zones is tracked using an array of 32bits
> zone write pointer offset attached to the scsi disk structure. Each
> entry of the array indicate a zone write pointer position relative to
> the zone start sector. The write pointer offsets are maintained in sync
> with the device as follows:
> 1) the write pointer offset of a zone is reset to 0 when a
>     REQ_OP_ZONE_RESET command completes.
> 2) the write pointer offset of a zone is set to the zone size when a
>     REQ_OP_ZONE_FINISH command completes.
> 3) the write pointer offset of a zone is incremented by the number of
>     512B sectors written when a write, write same or a zone append
>     command completes.
> 4) the write pointer offset of all zones is reset to 0 when a
>     REQ_OP_ZONE_RESET_ALL command completes.
> 
> Since the block layer does not write lock zones for zone append
> commands, to ensure a sequential ordering of the regular write commands
> used for the emulation, the target zone of a zone append command is
> locked when the function sd_zbc_prepare_zone_append() is called from
> sd_setup_read_write_cmnd(). If the zone write lock cannot be obtained
> (e.g. a zone append is in-flight or a regular write has already locked
> the zone), the zone append command dispatching is delayed by returning
> BLK_STS_ZONE_RESOURCE.
> 
> To avoid the need for write locking all zones for REQ_OP_ZONE_RESET_ALL
> requests, use a spinlock to protect accesses and modifications of the
> zone write pointer offsets. This spinlock is initialized from sd_probe()
> using the new function sd_zbc_init().
> 
> Co-developed-by: Damien Le Moal <Damien.LeMoal@wdc.com>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
> ---
>   drivers/scsi/sd.c     |  16 +-
>   drivers/scsi/sd.h     |  43 ++++-
>   drivers/scsi/sd_zbc.c | 363 +++++++++++++++++++++++++++++++++++++++---
>   3 files changed, 392 insertions(+), 30 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
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