Re: [RFC PATCH v2 2/4] block: block: change REQ_OP_ZONE_RESET_ALL from 8 to 15

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/05/16 12:55, Coly Li wrote:
> For a zoned device, e.g. host managed SMR hard drive, the request op
> REQ_OP_ZONE_RESET_ALL is to reset LBA of all zones' writer pointers to
> the start LBA of the zone they belong to. After all the write pointers
> are reset, all previously stored data is invalid and unaccessible.
> Therefore this op code changes on-disk data, belongs to WRITE request
> op code.
> 
> Similar to the problem of REQ_OP_ZONE_RESET, REQ_OP_ZONE_RESET_ALL is
> even number 8, it means bios with REQ_OP_ZONE_RESET_ALL in bio->bi_opf
> will be treated as READ request by op_is_write().
> 
> Same problem will happen when bcache device is created on top of zoned
> device like host managed SMR hard drive, bcache driver should invalid
> all cached data for the REQ_OP_ZONE_RESET_ALL request, but this zone
> management bio is mistakenly treated as READ request and go into bcache
> read code path, which will cause undefined behavior.
> 
> This patch changes REQ_OP_ZONE_RESET_ALL value from 8 to 15, this new
> odd number will make bcache driver handle this zone management bio in
> write request code path properly.
> 
> Fixes: e84e8f066395 ("block: add req op to reset all zones and flag")
> Signed-off-by: Coly Li <colyli@suse.de>
> Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Cc: Keith Busch <kbusch@kernel.org>
> ---
> Changelog:
> v2: fix typo for REQ_OP_ZONE_RESET_ALL.
> v1: initial version.
> 
>  include/linux/blk_types.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 8f7bc15a6de3..618032fa1b29 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -284,8 +284,6 @@ enum req_opf {
>  	REQ_OP_SECURE_ERASE	= 5,
>  	/* write the same sector many times */
>  	REQ_OP_WRITE_SAME	= 7,
> -	/* reset all the zone present on the device */
> -	REQ_OP_ZONE_RESET_ALL	= 8,
>  	/* write the zero filled sector many times */
>  	REQ_OP_WRITE_ZEROES	= 9,
>  	/* Open a zone */
> @@ -296,6 +294,8 @@ enum req_opf {
>  	REQ_OP_ZONE_FINISH	= 12,
>  	/* reset a zone write pointer */
>  	REQ_OP_ZONE_RESET	= 13,
> +	/* reset all the zone present on the device */
> +	REQ_OP_ZONE_RESET_ALL	= 15,

Same comment as for patch 1. And you can probably squash this patch into patch 1
to avoid repeating mostly the same explanation twice in the commit message.
REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL are very closely related. The latter
may actually be processed using the former anyway, so the op number change for
both should be a single patch to be consistent.

>  
>  	/* SCSI passthrough using struct scsi_request */
>  	REQ_OP_SCSI_IN		= 32,
> 


-- 
Damien Le Moal
Western Digital Research