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

FUJITA Tomonori
2009-05-12T15:05:49Z

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.