On Wed, Aug 25 2010 at  4:00am -0400,
Kiyoshi Ueda [off-list ref] wrote:

quoted

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?

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

I've refreshed Hannes' previous patchset against 2.6.36-rc2 but I
haven't finished testing it yet (should be OK.. it boots, but still have
FIXME to move scsi_uld_should_retry to scsi_error.c):
http://people.redhat.com/msnitzer/patches/dm-scsi-sense/

Would be great if James, Hannes and others had a look at this
refreshed RFC patchset.  It's clearly not polished but it gives an idea
of the approach.  Does this look worthwhile?

Follow-on work is needed to refine scsi_uld_should_retry further.  Keep
in mind that scsi_error.c is the intended location for this code.

James, please note that I've attempted to make REQ_TYPE_FS set
req->errors only for "genuine errors" by (ab)using
scsi_decide_disposition:
http://people.redhat.com/msnitzer/patches/dm-scsi-sense/scsi-Always-pass-error-result-and-sense-on-request-completion.patch

If others think this may be worthwhile I can finish testing, cleanup the
patches further, and post them.

Mike