linux-kernel - Re: [RFC][PATCH] fix sign extension with 1.5TB usb-storage LBD=y

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Date:	Tue, 21 Apr 2009 15:49:10 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	mdharm-usb@...-eyed-alien.net,
	linux-usb <linux-usb@...r.kernel.org>,
	usb-storage@...ts.one-eyed-alien.net,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [RFC][PATCH] fix sign extension with 1.5TB usb-storage LBD=y

On Tue, 2009-04-21 at 15:18 -0600, Matthew Wilcox wrote:
> 
> this certainly fixes your problem.  I'd prefer this patch instead, just
> because I find the cast unaesthetic ...
> 
> ----
> 
> Fix READ CAPACITY 10 with drives over 1TB
> 
> Shifting an unsigned char implicitly casts it to a signed int.  This
> caused 'lba' to sign-extend and Linux would then try READ CAPACITY 16
> which was not supported by at least one drive.  Making 'lba' an
> unsigned
> int ensures that sign extension will not occur.
> 
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 3fcb64b..c856b1b 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -1373,7 +1373,7 @@ static int read_capacity_10(struct scsi_disk
> *sdkp, struct scsi_device *sdp,
>         int sense_valid = 0;
>         int the_result;
>         int retries = 3;
> -       sector_t lba;
> +       unsigned lba;
>         unsigned sector_size;
> 
>         do {
> @@ -1413,7 +1413,7 @@ static int read_capacity_10(struct scsi_disk
> *sdkp, struct scsi_device *sdp,
>                 return -EOVERFLOW;
>         }
> 
> -       sdkp->capacity = lba + 1;
> +       sdkp->capacity = (sector_t)lba + 1;
>         return sector_size;
>  }

That's fine with me too.  This patch fixes my issue as well.

Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>

-- Dave

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