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

Dave Hansen
2009-04-21T22:49:27Z

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@linux.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@linux.vnet.ibm.com>

-- Dave