Re: ide-scsi command status bug

[Luben Tuikov <luben@splentec.com>]

Tony Battersby wrote:
> 
> Hello,
> 
> I have tracked down a problem with incorrect status being returned for a
> command sent through sg and ide-scsi.  I am using vanilla 2.4.17.  Here is
> what is happening:
> 
> The device returns CHECK CONDITION for a command sent to it from sg and
> ide-scsi.
> The following line executes in idescsi_end_request() in ide-scsi.c:
> pc->scsi_cmd->result = (CHECK_CONDITION << 1) | (DID_OK << 16);
> ide-scsi calls the callback completion function.
> An internal request sense is queued.
> The request sense completes successfully.
> The following line executes in idescsi_end_request() in ide-scsi.c:
> pc->scsi_cmd->result = (DID_OK << 16)
> ide-scsi calls the callback completion function for the request sense
> command.
> 
> In my userspace program, sg_io_hdr_t { status, masked_status } are both
> zero, but sg_io_hdr_t { driver_status } & DRIVER_SENSE is set and the sense
> data is valid.  It appears to me as if the status from the request sense
> command overwrote the original CHECK CONDITION status.  I verified this by
> forcing all request sense commands to return a status of 0x01 (reserved bit
> set) in idescsi_end_request() in ide-scsi.c, and sure enough, I got a status
> of 0x01 for the failed command in sg_io_hdr_t { status }.

You are relying on specific Linux SCSI core behaviour
rather than the spec. SPC-2, 7.20.1, specifies that if REQUEST
SENSE completed successfully, i.e. the sense data is valid, then
status GOOD is returned. If the status is CHECK CONDITION
for a completed REQUEST SENSE command then the sense data may NOT
be valid.

Simply: if you issue REQUEST SENSE and the command completes and
returns valid sense data, then you should get GOOD status.

You should NOT filter REQUEST SENSE and set status to CHECK CONDITION!
 
> I have not tested any other kernel versions.  I am working around the
> problem for now by faking a CHECK CONDITION status when driver_status &
> DRIVER_SENSE in my program.

In userspace you can pretty much make up your own rules.

-- 
Luben