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Subject: Re: [PATCH] scsi: core: Add BLIST_NO_ASK_VPD_SIZE for some VDASD
From:   Martin Wilck <mwilck@suse.com>
To:     "Martin K. Petersen" <martin.petersen@oracle.com>,
        Hannes Reinecke <hare@suse.de>
Cc:     Bart Van Assche <bvanassche@acm.org>,
        Lee Duncan <leeman.duncan@gmail.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Lee Duncan <lduncan@suse.com>
Date:   Mon, 21 Nov 2022 15:53:12 +0100
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         <4a1da181-8a54-d2f8-6d19-d9c1982ab044@suse.de>
         <yq1k046kwyv.fsf@ca-mkp.ca.oracle.com>
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On Mon, 2022-11-07 at 21:50 -0500, Martin K. Petersen wrote:
>=20
> Hannes,
>=20
> I have been contemplating this for a bit.
>=20
> > > Has it been considered instead of introducing a blacklist flag to
> > > not
> > > use the reported VPD page size if the device reports that the VPD
> > > page size is zero? I am not aware of any VPD pages for which zero
> > > is
> > > a valid size.
>=20
> That would also be my preferred approach, I think. I haven't received
> any bug reports about devices returning short VPD pages since this
> change was introduced. So I think I'd prefer falling back to a
> (hopefully small) default if a device returns a 0 page length.
>=20
> Now, my question is which VPD pages are actually supported by this
> device and how large are they?

I've tried to obtain an answer to this question from IBM, but they
couldn't come up with a concrete number for the page length. Especially
for VDASD devices, it's difficult to say, because these virtual devices
just pass the INQUIRY down to the backing device.

How do we proceed? Could we simply fall back to a page length of 255
bytes (like before c92a6b5d6335) if the reported page length is zero?

Regards,
Martin W.

>=20
> > But pre-SPC drives will ignore the VPD bit in the inquiry size. And
> > these devices do not set an additional length in the inquiry data
>=20
> Can you elaborate a bit on your experience with older devices? I
> checked
> SCSI-2 (1991) and don't see any indication this would be valid
> behavior
> even back then.
>=20