Re: [PATCH 03/11] block: add rq->resid_len

From: Boaz Harrosh <bharrosh@panasas.com>
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: tj@kernel.org, axboe@kernel.dk, linux-kernel@vger.kernel.org,
	jeff@garzik.org, linux-ide@vger.kernel.org,
	James.Bottomley@HansenPartnership.com,
	linux-scsi@vger.kernel.org, bzolnier@gmail.com,
	petkovbb@googlemail.com, sshtylyov@ru.mvista.com,
	mike.miller@hp.com, Eric.Moore@lsi.com,
	stern@rowland.harvard.edu, zaitcev@redhat.com,
	Geert.Uytterhoeven@sonycom.com, sfr@canb.auug.org.au,
	grant.likely@secretlab.ca, paul.clements@steeleye.com,
	tim@cyberelk.net, jeremy@xensource.com, adrian@mcmen.demon.co.uk,
	oakad@yahoo.com, dwmw2@infradead.org, schwidefsky@de.ibm.com,
	ballabio_dario@emc.com, davem@davemloft.net,
	rusty@rustcorp.com.au, Markus.Lidel@shadowconnect.com,
	dgilbert@interlog.com, djwong@us.ibm.com
Subject: Re: [PATCH 03/11] block: add rq->resid_len
Date: Tue, 12 May 2009 18:08:17 +0300	[thread overview]
Message-ID: <4A0990E1.7080508@panasas.com> (raw)
In-Reply-To: <20090513000150H.fujita.tomonori@lab.ntt.co.jp>

On 05/12/2009 06:00 PM, FUJITA Tomonori wrote:
> On Tue, 12 May 2009 11:58:28 +0300
> Boaz Harrosh <bharrosh@panasas.com> wrote:
> 
>> On 05/11/2009 05:59 PM, FUJITA Tomonori wrote:
>>> On Mon, 11 May 2009 14:31:41 +0300
>>> Boaz Harrosh <bharrosh@panasas.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.

Please read my full reply, I said yes old code was better, but not
good enough, error status must be returned also in this case.

This code is already submitted are you sending a fix?

Thanks
Boaz