Re: [PATCH v4] sd: Check for unaligned partial completion

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Thu, 2017-02-16 at 11:52 +0900, Damien Le Moal wrote:
> Thanks for the pointers. I checked libiscsi tests. And from what is done
> there, it seems to me that it is basically impossible to distinguished
> between a buggy hardware response and an in-purpose (or buggy) not
> aligned data-out buffer size.
> E.g. the test in test_write10_residuals.c which issues a 1 block write
> with a buf size of 10000 and checks that residual is 10000 - block size.
> For that case, with both this patch and the original mpt3sas patch, the
> rounding up of resid to the block size will break the test.
> 
> Yet, it is very surprising that LIO and SCST_SCSI issue the "buggy"
> request as is without checking and eventually correcting things first.
> So unless LIO and SCST_SCSI are fixed to do that on the request they
> send to the device, both patches should be dropped.
> Users with buggy mpt3 HBAs will need to update the HBA FW...
> 
> So the conclusion may be that we need to drop everything ? The mpt3sas
> patch breaks ZBC now, so that must be removed too.

Hello Damien,

For the example you cited (bufflen - residual) = block size. This is
why I proposed to round (bufflen - residual) instead of residual. Whether
bufflen or (bufflen - residual) is rounded doesn't matter if bufflen is a
multiple of the logical block size. But it matters if bufflen is not a
multiple of the logical block size.

Bart.