linux-kernel - Re: [PATCH 03/11] block: add rq->resid

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Message-Id: <20090513000150H.fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 13 May 2009 00:00:47 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	bharrosh@...asas.com
Cc:	fujita.tomonori@....ntt.co.jp, tj@...nel.org, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
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	djwong@...ibm.com
Subject: Re: [PATCH 03/11] block: add rq->resid_len

On Tue, 12 May 2009 11:58:28 +0300
Boaz Harrosh <bharrosh@...asas.com> wrote:

> On 05/11/2009 05:59 PM, FUJITA Tomonori wrote:
> > On Mon, 11 May 2009 14:31:41 +0300
> > Boaz Harrosh <bharrosh@...asas.com> wrote:
> > 
> >>>>> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> >>>>> index 3da02e4..6605ec9 100644
> >>>>> --- a/drivers/scsi/libsas/sas_expander.c
> >>>>> +++ b/drivers/scsi/libsas/sas_expander.c
> >>>>> @@ -1936,12 +1936,8 @@ int sas_smp_handler(struct Scsi_Host *shost, struct sas_rphy *rphy,
> >>>>>  			       bio_data(rsp->bio), rsp->data_len);
> >>>>>  	if (ret > 0) {
> >>>>>  		/* positive number is the untransferred residual */
> >>>>> -		rsp->data_len = ret;
> >>>>> -		req->data_len = 0;
> >>>>> +		rsp->resid_len = ret;
> >>>>>  		ret = 0;
> >>>>> -	} else if (ret == 0) {
> >>>>> -		rsp->data_len = 0;
> >>>>> -		req->data_len = 0;
> >>>>>  	}
> >>>>>  
> >>>>>  	return ret;
> >>>> This is actually a bug fix, as well as a strait conversion
> >>> Can you elaborate a bit about the bug fix part?
> >>>
> >> Nothing big really, just that before (according to the comment), the theoretical
> >> negative case would be full-residual. and now it is zero (untouched).
> >>
> >> I know that in iscsi a negative residual is possible which means over-flow. That is:
> >> the target had more data to give then the buffer had space for. (which is not an error at all)
> > 
> > Hmm, iSCSI? This code is for SAS management Protocol.
> > 
> 
> I gave that as an example of what the scsi standard says about negative
> residual count return from the target. If SAS as sepecific and different
> meaning to negative residual, it should be noted and handled.

Please read the code first.

If sas_smp_handler() returns a negative value, a lld doesn't transfer
anything. The original code used full-residual. The original code is
fine. Your 'this is a bug fix' claim is wrong. We need to revert the
original behavior though.
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