On 08/30/05 06:26, Tejun Heo wrote: > Albert Lee wrote: > >>>4. Corresponding scmd's result code is set to >>> SAM_STAT_CHECK_CONDITION and qc->scsidone() callback is called >>> directly. As we haven't filled sense data, >>> scsi_determine_disposition() will return FAILED and SCSI EH will >>> be scheduled. Note that as we directly call qc->scsidone(), qc is >>> left intact. >>> >>> >> >>Could we get the sense data before calling qc->scsidone()? (Using the >>proposed separate >>EH qc can keep the original qc intact.) >> >>The issue: >>When a DVD drive returns MEDIUM_ERROR in the sense data, libata doesn't >>retry the command. >> >>For libata, when scsi_softirq() calls scsi_decide_disposition() and >>scsi_check_sense() to determine >>how to handle the result, scsi_check_sense() always returns "fail" since >>the sense data is not there >>yet. The sense data is requested later in the libata error handler. But >>the command has already been >>considered as an "error". >> >>By having the sense data ready before calling qc->scsidone(), we can >>make the >>NEEDS_RETRY work in scsi_softirq(). So, for things like MEDIUM_ERROR, >>the device has >>a chance to retry/recover the error. This seems to be important for >>devices with built-in >>defect management system. > > > There are two ways a scmd can leave EH - retry by scsi_queue_insert() > and finish by scsi_finish_cmd(). I think the problem you described can > be easily solved by choosing the former method when finishing the qc > from EH. Note that other advanced EH stuff like reconfiguring transport > speed also requires retrying, so we will surely have a mechanism for > retrying failed qc's from EH. What is needed is autosense simulation for ATA, so that SCSI Core doesn't know that the device doesn't support autosense. So, before a failed command reaches SCSI Core recovery, it should pass by ATA layer recovery to get sense. Note: if you send another command for execution after the failed command _and_ no autosense is provided, then any sense data is lost -- this is further subject to more rules set forth in SAM and SPC. Luben - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
