Re: [PATCH][BUG] Incorrect SCSI transfer length computation from odd sized scsi_execute_async() transfers.

[Mike Christie <michaelc@cs.wisc.edu>]

Jeremy Linton wrote:
> Any function which use scsi_execute_async() and transfers "odd" sized 
> data that doesn't align correctly with the segment sizes may have its 
> transfer length padded out to the closest segment size.
>
> For writes, this results in unnecessary data being transfered to the 
> SCSI target. For reads, it affects the residual data length being 
> returned to the application since the residual length will be based on 
> the padded transfer size rather than the actual request size.
>
> The easiest way to see this is by trying to read using the SG_IO ioctl a 
> large (>32k) buffer size from a tape device that only has a few bytes of 
> data stored for the current block. The resulting resid will generally be 
> incorrect.
>
> I've fixed this simply by changing scsi_req_map_sg() so that it places 
> the requested transfer length in rq->data_len rather than the sum of all 
> the sg segments.
>
> This patch applies against scsi_lib.c in 2.6.22.
>
> Signed-off-by: Jeremy Linton <jli@greshamstorage.com>
>
>
> --- linux-2.6.22/drivers/scsi/scsi_lib.c.orig   2007-07-11 
> 19:07:06.000000000 -0500
> +++ linux-2.6.22/drivers/scsi/scsi_lib.c        2007-07-11 
> 18:43:36.000000000 -0500
> @@ -350,7 +350,7 @@ static int scsi_req_map_sg(struct reques
>         }
>
>         rq->buffer = rq->data = NULL;
> -       rq->data_len = data_len;
> +       rq->data_len = bufflen;
>         return 0;

I think you needed some other bits in there. See this patch 
http://marc.info/?l=linux-scsi&m=117392208211297&w=2

I tried just setting the bufflen first, and that still had problems. 
Could you try the patch here

http://marc.info/?l=linux-scsi&m=117392208211297&w=2
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