linux-kernel - Re: [PATCH] sd: remove redundant check for BLK_DEF_MAX

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Date:	Sat, 4 Jun 2016 16:41:23 +0800
From:	Tom Yan <tom.ty89@...il.com>
To:	Long Li <longli@...rosoft.com>
Cc:	"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sd: remove redundant check for BLK_DEF_MAX_SECTORS

The main point there is not to check q->limits.max_sectors against
BLK_DEF_MAX_SECTORS, but sdkp->opt_xfer_blocks against
SD_DEF_XFER_BLOCKS et al.? `rw_max = BLK_DEF_MAX_SECTORS;` there is
merely the fallback when sdkp->opt_xfer_blocks does not pass the
conditions. With your patch `rw_max` can be indeterminate in those
circumstances.

On 4 June 2016 at 11:57, Long Li <longli@...rosoft.com> wrote:
> q->limits.max_sectors is already checked against BLK_DEF_MAX_SECTORS in __scsi_alloc_queue(), when it calls blk_queue_max_hw_sectors(). There is no need to check it again in sd.
>
> This change also allows a SCSI driver set an maximum sector size bigger than BLK_DEF_MAX_SECTORS, without returning values on optional VPD page 0xb0 "Block Limits".
>
> Signed-off-by: Long Li <longli@...rosoft.com>
>
> ---
>  drivers/scsi/sd.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 60bff78..d8c4047 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2870,11 +2870,8 @@ static int sd_revalidate_disk(struct gendisk *disk)
>             logical_to_bytes(sdp, sdkp->opt_xfer_blocks) >= PAGE_SIZE) {
>                 q->limits.io_opt = logical_to_bytes(sdp, sdkp->opt_xfer_blocks);
>                 rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks);
> -       } else
> -               rw_max = BLK_DEF_MAX_SECTORS;
> -
> -       /* Combine with controller limits */
> -       q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
> +               q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
> +       }
>
>         set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity));
>         sd_config_write_same(sdkp);
> --
> 2.7.4
>
> --
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