Bart,
On 2019/10/28 21:38, Bart Van Assche wrote:
> On 10/28/19 3:57 AM, Damien Le Moal wrote:
>> struct scsi_cmnd cmd->req.resid_len which is returned and set
>> respectively by the helper functions scsi_get_resid() and
>> scsi_set_resid() is an unsigned int. Reflect this fact in the interface
>> of these helper functions.
>> [ ... ]
>> -static inline void scsi_set_resid(struct scsi_cmnd *cmd, int resid)
>> +static inline void scsi_set_resid(struct scsi_cmnd *cmd, unsigned int resid)
>> {
>> cmd->req.resid_len = resid;
>> }
>>
>> -static inline int scsi_get_resid(struct scsi_cmnd *cmd)
>> +static inline unsigned int scsi_get_resid(struct scsi_cmnd *cmd)
>> {
>> return cmd->req.resid_len;
>> }
>
> From the iSCSI RFC:
>
> SCSI-Presented Data Transfer Length (SPDTL) is the term this document
> uses (see Section 1.1 for definition) to represent the aggregate data
> length that the target SCSI layer attempts to transfer using the
> local iSCSI layer for a task. Expected Data Transfer Length (EDTL)
> is the iSCSI term that represents the length of data that the iSCSI
> layer expects to transfer for a task. EDTL is specified in the SCSI
> Command PDU.
>
> When SPDTL = EDTL for a task, the target iSCSI layer completes the
> task with no residuals. Whenever SPDTL differs from EDTL for a task,
> that task is said to have a residual.
>
> If SPDTL > EDTL for a task, iSCSI Overflow MUST be signaled in the
> SCSI Response PDU as specified in [RFC3720]. The Residual Count MUST
> be set to the numerical value of (SPDTL - EDTL).
>
> If SPDTL < EDTL for a task, iSCSI Underflow MUST be signaled in the
> SCSI Response PDU as specified in [RFC3720]. The Residual Count MUST
> be set to the numerical value of (EDTL - SPDTL).
>
> Note that the Overflow and Underflow scenarios are independent of
> Data-In and Data-Out. Either scenario is logically possible in
> either direction of data transfer.
>
> If the residual is changed from signed into unsigned, how is a SCSI LLD
> expected to report the difference between residual overflow and residual
> underflow to the SCSI core?
As mentioned in the commit message, cmd->req.resid_len where the resid
is stored is an unsigned int. And it has been an unsigned int forever as
far as I know.
So I think changing the interface to unsigned int makes sense in that
context. Also, unless I am reading this wrong, the above definition you
quote always lead to resid >= 0, so I do not see what problem you are
worried about. Could you elaborate your concerns please ?
>
> Thanks,
>
> Bart.
>
--
Damien Le Moal
Western Digital Research
