linux-kernel - Re: [PATCH v2] libata: Simulate REPORT LUNS for ATAPI devices

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Message-ID: <457867C5.7060508@torque.net>
Date:	Thu, 07 Dec 2006 14:13:09 -0500
From:	Douglas Gilbert <dougg@...que.net>
To:	James Bottomley <James.Bottomley@...elEye.com>
CC:	"Darrick J. Wong" <djwong@...ibm.com>,
	Jeff Garzik <jeff@...zik.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v2] libata: Simulate REPORT LUNS for ATAPI devices

James Bottomley wrote:
> On Mon, 2006-12-04 at 15:32 -0800, Darrick J. Wong wrote:
>> The Quantum GoVault SATAPI removable disk device returns ATA_ERR in
>> response to a REPORT LUNS packet.  If this happens to an ATAPI device
>> that is attached to a SAS controller (this is the case with sas_ata),
>> the device does not load because SCSI won't touch a "SCSI device"
>> that won't report its LUNs.  Since most ATAPI devices don't support
>> multiple LUNs anyway, we might as well fake a response like we do for
>> ATA devices.
> 
> Actually, there may be a standards conflict here.  SPC says that all
> devices reporting compliance with this standard (as the inquiry data for
> this device claims) shall support REPORT LUNS.  On the other hand, MMC
> doesn't list REPORT LUNS in its table of mandatory commands.

MMC-5 rev 4 section 7.1:
"Some commands that may be implemented by MM drives are
not described in this standard, but are found in other
SCSI standards. For a complete list of these commands
refer to [SPC-3]."

Hmm, "may be implemented" yet REPORT LUNS is mandatory
in SPC-3 (and SPC-3 is a normative reference for MMC-5).
I guess there is wriggle room there.
In practice, MMC diverges from SPC a lot more than other
SCSI device type command sets (e.g. SBC and SSC).

> I'm starting to think that even if they report a SCSI compliance level
> of 3 or greater, we still shouldn't send REPORT LUNS to devices that
> return MMC type unless we have a white list override.

There is also SAT compliance. For the ATA command set (i.e.
disks) sat-r09 lists REPORT LUNS and refers to SPC-3. For
ATAPI sat-r09 is far less clear. It does recommend, for
example, that the ATA Information VPD pages is implemented
in the SATL for ATAPI devices.

Doug Gilbert
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