Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16

Martin K. Petersen
2014-07-16T17:47:35Z

>>>>> "Christoph" == hch@infradead org <hch@infradead.org> writes:

Christoph> Oh, we actually have devices that support WRITE SAME with
Christoph> unmap, but not without? That's defintively a little strange.

Yep :(

There were several SSDs that did not want to support wearing out flash
by writing gobs of zeroes and only support the UNMAP case.

Christoph> Yes, and it did this intentionally. I really wouldn't expect
Christoph> devices to support WRITE SAME with UNMAP but blow up on a
Christoph> WRITE SAME without it (and not just simple fail it in an
Christoph> orderly way).

*sigh*

Christoph> It definitively seems odd to default to trying WRITE SAME for
Christoph> unmap for a device that explicitly tells us that it doesn't
Christoph> support WRITE SAME.

Maybe it's just a naming thing. I was really trying to convey
no_req_write_same support, not no_write_same_10_or_16.

Christoph> Note that I'm not against your patch - I suspect forcing us
Christoph> to read EVPD pages even for devices that claim to be SPC-2
Christoph> will come in useful in various scenarios.

I don't have a problem with a BLIST_PREFER_UNMAP flag or something like
that. But BLIST_TRY_VPD_PAGES seems more generally useful and it does
fix the problem at hand. That's why I went that route.

--
Martin K. Petersen Oracle Linux Engineering