Re: [PATCH] scsi: Fix scsi_get/set_resid() interface

[Bart Van Assche <bvanassche@acm.org>]

On 10/30/19 8:18 AM, Hannes Reinecke wrote:
> On 10/30/19 4:12 PM, Bart Van Assche wrote:
>> I do not agree that reporting a residual overflow by calling 
>> scsi_set_resid(..., 0) is acceptable. For reads a residual overflow 
>> means that the length specified in the CDB (scsi_bufflen()) exceeds 
>> the data buffer size (length of scsi_sglist()). I think it's dangerous 
>> to report to the block layer that such requests completed successfully 
>> and with residual zero.
>>
> But that is an error on submission, and should be aborted before it even 
> got send to the drive.

If such a bug ever gets introduced in the SCSI core, I think that SCSI 
target code should detect and report it. If the SCSI core receives a 
response with a residual overflow it can then take appropriate action, 
e.g. call WARN_ON_ONCE().

Users of sg_raw can trigger the residual overflow case easily.

> However, this does not relate to the residual, which is handled after 
> the command completes (and which sparked this entire thread ...).

I'm still waiting for an answer to my question of how SCSI LLDs are 
expected to report a residual overflow to the SCSI core.

Thanks,

Bart.