[dm-devel] [PATCH] multipath: Evaluate request result and sense code

[Hannes Reinecke]

Mike Christie wrote:
> Hannes Reinecke wrote:
>> As we now see the result for every command we
>> can use it to make some more elaborate choices
>> if we should retry the request on another path.
>>
>> This solves a potential data corruption when
>> a request is being terminated with RESERVATION
>> CONFLICT and queue_if_no_path is active; the
>> request will be queued until the reservation
>> status changes and then transmitted.
> 
> 
> I had the same bz. To handle it I just converted the error to some other
> -EXYZ value. But like I said in my patch that I sent to the list I did
> not like it much.
> 
Yeah, that was my thought, too.
The scsi result codes simply don't fit on the -EXXX values.

> I thought of going the route you did in this patch, but thought it was
> too scsi specific. Does dasd want advanced error handling? If not, then
> I am fine since for hw handlers we assume they are always scsi_dh modules.
Well, DASD has it's own sort of problems; basically DASD will _always_
try to do it's own internal recovery by waiting for the storage array
to respond. So with DASD we basically only ever have three states:
- GOOD
- Failure as being evaluated by the _storage array_
- Don't know (if failfast is set)
And any advanced checking won't give us much here, as either the link
is on-line and we have details about the error or the link is severed
and we don't know anything.

But there's a good point, we should be doing some sort of
cross-check to determine if it really is a SCSI error.
Just to prevent any accidental spill-overs in the future.

I'll be sending a patch.

Cheers,

Hannes
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-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
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