Re: [PATCH] extracting resid from struct scsi_cmnd

[Jens Axboe <axboe@suse.de>]

On Sun, Nov 28 2004, Douglas Gilbert wrote:
> Jens Axboe wrote:
> >On Sun, Nov 28 2004, Douglas Gilbert wrote:
> >
> >>Jens,
> >>While on the subject of extracting info from struct scsi_cmnd
> >>I have noticed that scsi_cmnd::resid doesn't make it into
> >>sg_io_hdr::resid in the block layer SG_IO implementation.
> >>"rq->data_len" is put there instead and it invariably has a
> >>value of 0.
> >>
> >>"struct request" does not have a 'resid' field which is defined
> >>as the number of bytes requested to be transferred less the actual
> >>number transferred.
> >
> >
> >->data_len is that value, after execution of the request. If rq->data_len
> >== 0 for a SCSI request that with residual bytes, then that's a bug.
> 
> Jens,
> Ok, it looks like a bug then. Here is an example with the
> scsi_debug version I just sent to this list and a recent sg3_utils
> (e.g. v1.11 beta at the top of http://www.torque.net/sg ).
> That scsi_debug version sets resid and sg3_utils reports resid != 0
> when the verbose flag is given.
> 
> Here is what I am seeing:
> 
> # sg_inq -v /dev/sg0
>      inquiry cdb: 12 00 00 00 24 00
> ...
>   Product identification: scsi_debug
>   Product revision level: 0004
>      inquiry cdb: 12 01 00 00 fc 00
>      inquiry: resid=124
>      inquiry cdb: 12 01 80 00 fc 00
>      inquiry: resid=124
>   Unit serial number: 2000
> 
> # sg_inq -v /dev/sda
>      inquiry cdb: 12 00 00 00 24 00
> ...
>   Product identification: scsi_debug
>   Product revision level: 0004
>      inquiry cdb: 12 01 00 00 fc 00
>      inquiry cdb: 12 01 80 00 fc 00
>   Unit serial number: 2000
> 
> So the sg driver indicates that of the 252 bytes
> requested (for VPD pages 0x0 and 0x80) only 128 bytes
> were returned [and 128 bytes is an over-allowance by
> scsi_debug for those pages]. The sd driver remains silent
> implying resid is 0 .
> 
> rq->data_len is only written in one place in the scsi mid level
> (in scsi_io_completion() inside scsi_lib.c). The attached
> patch places cmd->resid into rq->data_len (rather than decrementing
> it by cmd->bufflen) and fixes the problem shown above. I then
> built a file system on the scsi_debug virtual disk and copied
> files to and from it and there were no ill effects.
> 
> Changelog:
>    - during successful command completion place resid from SCSI
>      LLDs into request::data_len so that block SG_IO ioctl reports
>      resid
> 
> Doug Gilbert
> 
> 
> 

> --- linux/drivers/scsi/scsi_lib.c	2004-11-15 20:53:03.000000000 +1000
> +++ linux/drivers/scsi/scsi_lib.c2610rc2resid	2004-11-28 22:12:22.070160152 +1000
> @@ -728,7 +728,7 @@
>  				req->sense_len = len;
>  			}
>  		} else
> -			req->data_len -= cmd->bufflen;
> +			req->data_len = cmd->resid;
>  	}
>  
>  	/*
> 

Patch looks correct, thanks Doug.

-- 
Jens Axboe