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

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Message-Id: <20090511235852Z.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 11 May 2009 07:59:10 -0700 (PDT)
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	bharrosh@...asas.com
Cc:	tj@...nel.org, axboe@...nel.dk, linux-kernel@...r.kernel.org,
	jeff@...zik.org, linux-ide@...r.kernel.org,
	James.Bottomley@...senPartnership.com, linux-scsi@...r.kernel.org,
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	Markus.Lidel@...dowconnect.com, dgilbert@...erlog.com,
	djwong@...ibm.com
Subject: Re: [PATCH 03/11] block: add rq->resid_len

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.

smp_execute_task returns a negative value for some errors (ENOMEM, the
hardware doesn't respond, etc). It's not related with 'transferred
buffer length' at all.
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