Re: [PATCH 1/2] target: Don't arbitrary limit I/O size to fabric_max_sectors

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On Fri, 2015-01-09 at 15:43 -0500, Martin K. Petersen wrote:
> >>>>> "nab" == Nicholas A Bellinger <nab@xxxxxxxxxxxxxxx> writes:
> 
> nab> The concern is when older hardware drivers are reporting say
> nab> queue_max_hw_sectors=128 with initiators are not actively honoring
> nab> block limits EVPD MAXIMUM TRANSFER LENGTH, that would result in
> nab> I/Os over 64K generating exception status.
> 
> Given that you're already splitting I/Os in IBLOCK I think it would
> probably be better to pick a size you're comfortable with. 4 or 8 megs
> sound reasonable to be
> 

I'm now thinking to go just ahead and drop the hw_max_sectors check in
sbc_parse_cdb() as well, and leave hw_max_sectors as a purely
informational attribute representing the granularity each backend driver
and/or subsystem is splitting I/Os upon.

Which would mean there is no longer a maximum I/O size enforced by the
target.  This used to be the case in < v3.5 code, before Roland added
fabric_max_sectors to enforce the global 4 MB maximum that people
recently have been starting to run up against with initiators not
honoring block limits VPD.

That said, I don't recall there being any issues with the earlier code
not enforcing a maximum I/O size, so in order to avoid the same problem
in the future it probably makes the sense to go ahead process any
arbitrary sized I/O.

Re-spinning a -v2 with this in mind.

--nab






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