[dm-devel] Re: [RFC PATCH 4/4] convert scsi to blkerr error values

[Mike Christie]

goggin, edward wrote:
> Mike,
> 
> I don't think it is reasonably possible to anticipate
> all possible parsing requirements for the asc and ascq
> portions of SCSI sense information across all device
> models.  I'm in favor of having a "small" framework in
> SCSI where a SCSI sense interpreter module (per
> vendor & model possibly) could be registered
> dynamically, by dm-emc.c for instance.

Yeah I agree, I mentioned this before in some other mails. I think a 
module versus some table that userspace could write to were discussed.

The BLKERR values were meant to be able to tell upper layer code whether 
a transport or device or driver error occured and whether the lower 
level thought it was retryable. But then I thought I could also wedge in 
the handling of the vendor specifcs by adding a vendor specific SCSI 
module that would map the their specific value to a BLKERR_* one. And as 
I said offlist it is not working perfectly becuase we are losing some 
information in the translations.

> 
> The extended error interpreter callout would be
> triggered indirectly by a call from
> __end_that_request_first to a extended error parser
> associated with the io request's queue whenever it
> sees a non-zero sense field of the io request.
> Perhaps the sense and sense_len fields in the
> request structure should be changed to not be
> SCSI specific.

So this just handles the sense type of error right? We still need 
something seperate for the transport and device etc errors correct?

> 
> Also, in order to allow for more variation and detail
> in the interpretation of device specific SCSI asc and
> ascq values, the results of the interpretation should
> not be required to be block layer generic, but instead
> are saved in something like a void *bi_extended_error
> field of the bio.  __end_that_request_first would push
> the results of the extended_error interpretation to the
> bi_extended_error field of each bio in the request,
> similar to how Jens's code currently works.
> 
> This extended error parsing approach should extend easily
> (without requiring a kernel revision for new BLKERR values)
> to new SCSI devices/models and their device specific asc
> and ascq values.  This design could also be extended to
> support the interpretation of extended error information
> for non-SCSI block devices like DASD.
> 

I am fine with such a thing. You basically described what we have been 
talking about for some time but sperated the BLKERR part from the vendor 
specific part (which solves the problem I was having in trying to use 
the BLKERR value for two things). I am not the decision maker though so.