Re: scsi error handling thread and REQUEST SENSE

[Hannes Reinecke <hare@suse.de>]

On 05/19/2014 12:29 PM, Bart Van Assche wrote:
> On 05/19/14 10:32, Hannes Reinecke wrote:
>> Well, problem here is that the 'REQUEST SENSE' command has two problems:
>> a) Most modern HBA (ie all non-SPI HBAs) use autosense, ie the sense
>> code is returned with the command. So issuing 'REQUEST SENSE' here is
>> pointless.
>> b) The sense code (when retrieved via 'REQUEST SENSE') relates to the
>> most recently processed command (from the target perspective).
>> Which is a bit hard to make out, as by the time SCSI EH starts
>> several other commands might have been processed already, so any
>> sense we'd be retrieving most likely does not relate to the failed command.
>>
>> I would propose to disable the 'REQUEST_SENSE' step as soon as the HBA
>> is capable of autosensing. We requires us to add another flag
>> to the scsi_host field.
>>
>> What about the attached patch? That should roughly do what's required
>> here, right?
>
> This patch does not address the SRP initiator. There might be more SCSI
> initiator drivers that support autosense but that are not addressed by
> this patch. Has it been considered to set the autosense flag for all
> HBA's and clear it in those SCSI initiator drivers that do not support
> autosense ?
>
Correct.
I haven't looked at the SRP spec to figure out if it does autosense 
or not. If it does we should be updating the patch.

And yes, it has been considered.
However, I decided against it because it would require to check
each and every driver to figure out if they do autosense or not.
So as a first test I decided it to be quicker to have a 'whitelist' 
kind of approach and enable only those for which autosense is 
required by protocol.

This also excludes all RAID HBAs, which need to be checked 
individually. And the SPI HBAs, of course.

Plus this is just a test patch, nothing official yet.
I'm happy to include the changes for SRP if you can confirm that SRP 
requires autosense.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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