Re: [dm-devel] Re: [BUG] dm-mpath and scsi persistent reservation

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

James Bottomley wrote:
>> I don't see how we could use a device handler to translate an scsi error
>> code from a write io submitted to the multipath device map. Do you ?
> 
> Well, there is a problem.  Reservation Conflict should be treated as a
> device error and passed straight up ... it shouldn't really have any
> effect on dm mp because a path switch is unlikely to fix any issues.  So
> dm mp shouldn't be intercepting this type of error at all.
> 

I think what Christophe was asking for is something like this:

[RFC PATCH 1/4] convert block layer drivers to blkerr
http://marc.info/?l=linux-scsi&m=112487427230642&w=2
[RFC PATCH 2/4] convert dm to blkerr error values
http://marc.info/?l=linux-scsi&m=112487427306501&w=2
[RFC PATCH 3/4] convert dm-multipath to blkerr error
http://marc.info/?l=linux-scsi&m=112487431524436&w=2
[RFC PATCH 4/4] convert scsi to blkerr error values
http://marc.info/?l=linux-scsi&m=112487431524350&w=2

something that allows lower layers to give the upper layers some extra 
info. In the patches the scsi layer would return a fatal device error, 
and device mapper multipath would see that and just fail the IO instead 
of retrying on a new path.

I do not like my implementation in those patches, but I did not have 
time in the past to rework them. I can now though if you guys have any 
comments. I am really struggling on the definition of the block layer 
errors codes and what info they should convey. For example I was not 
sure if they should they give a hint about if the error is fatal or 
retryable like in the patches above or should they describe what happened?