Re: blk_integrity_revalidate() clears BDI_CAP_STABLE_WRITES

On Fri, Feb 24, 2017 at 12:49 AM, Martin K. Petersen
[off-list ref] wrote:

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"Ilya" == Ilya Dryomov [off-list ref] writes:

Ilya,

Ilya> Well, blk_integrity_revalidate() doesn't clear the profile, it
Ilya> just clears the stable pages flag.  Whoever calls
Ilya> blk_integrity_unregister() to clear the profile can also clear the
Ilya> stable pages flag -- why not let blk_integrity_unregister() clear
Ilya> the flag like I suggested?

That's what it used to do.

blk_integrity_revalidate() was obviously introduced to overcome some
problem. Unfortunately, I can't recall what that was and Google isn't
being particularly helpful. I suspect it was either in the NVDIMM or
NVMe camps since that's where the churn was.

Adding more people from 25520d55cdb6 -- does anyone remember the story
behind blk_integrity_revalidate()?

I don't have a problem with your patch as long as we're sure there are
no regressions. I would carry the gendisk check over, though.

I spent quite some time trying to do basic tests on nvme, since it uses
both nop_profile and real integrity profiles.  Unfortunately I don't
have access to an nvme card with separate-metadata capability and
upstream qemu driver doesn't support any metadata capabilities at all,
so I turned to https://github.com/OpenChannelSSD/qemu-nvme.  It lets
you configure mc and multiple lbafs, but

    commit ff646a5841f743fdd9cfef138ac6be1f0ba4fbfb
    Author: Keith Busch [off-list ref] Thu Oct 23 20:02:44 2014

    As part of this, I am removing all meta-data support. It's not well
    supported in any immediatly available operating system, so the code
    is not well tested.

In the end I got it into a semi-working state by checking out an old
version and dropping some sanity checks.  I formatted the namespace in
a number of ways -- bdi/stable_pages_required and integrity/format
behaved as expected ("none", "nop", "T10-DIF-TYPE1-CRC").

Given the above, I'm not sure what the baseline is -- blk_integrity
code isn't invoked for data-only lbafs.  Could nvme folks please look
at this?  rbd regression caused by integrity revalidate change goes
back to 4.4 and I'd really like to get it fixed.  The proposed patch
is attached to my earlier reply on linux-block.

Thanks,

                Ilya