Re: [RFC] training mpath to discern between SCSI errors

[Mike Christie <michaelc@cs.wisc.edu>]

On 08/25/2010 10:59 AM, Mike Snitzer wrote:
> On Wed, Aug 25 2010 at  4:00am -0400,
> Kiyoshi Ueda<k-ueda@ct.jp.nec.com>  wrote:
>
>>> I'm not sure how to proceed here.  How much work would
>>> discerning between transport and IO errors take?  If it can't be done
>>> quickly enough the retry logic can be kept around to keep the old
>>> behavior but that already was a broken behavior, so...  :-(
>>
>> I'm not sure how long will it take.
>
> We first need to understand what direction we want to go with this.  We
> currently have 2 options.  But any other ideas are obviously welcome.
>
> 1)
> Mike Christie has a patchset that introduce more specific
> target/transport/host error codes.  Mike shared these pointers but he'd
> have to put the work in to refresh them:
> http://marc.info/?l=linux-scsi&m=112487427230642&w=2
> http://marc.info/?l=linux-scsi&m=112487427306501&w=2
> http://marc.info/?l=linux-scsi&m=112487431524436&w=2
> http://marc.info/?l=linux-scsi&m=112487431524350&w=2
>
> errno.h new EXYZ
> http://marc.info/?l=linux-kernel&m=107715299008231&w=2
>
> add block layer blkdev.h error values
> http://marc.info/?l=linux-kernel&m=107961883915068&w=2
>
> add block layer blkdev.h error values (v2 convert more drivers)
> http://marc.info/?l=linux-scsi&m=112487427230642&w=2
>
> I think that patchset's appoach is fairly disruptive just to be able to
> train upper layers to differentiate (e.g. mpath).  But in the end maybe
> that change takes the code in a more desirable direction?

I think it is more disruptive, but is the cleaner approach in the end.

#2 looks hacky. In upper layers, we will have checks for dasd and other 
AOE and other drivers. And then #2 does not even work for filesystems 
(ext said they need this).



>
> 2)
> Another option is Hannes' approach of having DM consume req->errors and
> SCSI sense more directly.
>