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



Mike Christie wrote:
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.


Oh yeah so the problem I am having is emc boxes may return "LUN Not Ready - Manual Intervention Required". When dm-emc.c sees this error it wants to bypass a group of paths and retry the IO but under ceratin conditions not fail those paths. So I am not sure what to return for this error. I thought if I redo my BLKERR so they describe the error like

BLKERR_DEV_NOT_READY
BLKERR_MANUAL_INTERVENTION_REQ
BLKERR_NOT_CONN

... and set them up as a bitmap like suggested by JamesB. I could return
BLKERR_MANUAL_INTERVENTION_REQ from a scsi module then have dm-emc.c evaluate that value to a dm-mpaths return value of "MP_BYPASS_PG | MP_RETRY_IO" which means bypass the priority group (group of paths) and retry the IO.

But as more vendors use dm and they cannot use existing BLKERR values I have to add more and more. And then we have to handle the case where some block layer code may return BLKERR_MANUAL_INTERVENTION_REQ for something not related to the reasons EMC's HW was returning "LUN Not Ready - Manual Intervention Required" and we end up with getting things wrong.


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