Re: [PATCH] scsi: Add QEMU CD-ROM to VPD Inquiry Blacklist

[Hannes Reinecke <hare@suse.de>]

On 06/06/2016 04:11 PM, Ewan D. Milne wrote:
> 
> 
> On Mon, 2016-06-06 at 09:34 +0200, Hannes Reinecke wrote:
>> On 05/31/2016 03:42 PM, Ewan D. Milne wrote:
>>> Linux fails to boot as a guest with a QEMU CD-ROM:
>>>
>>> [    4.439488] ata2.00: ATAPI: QEMU CD-ROM, 0.8.2, max UDMA/100
>>> [    4.443649] ata2.00: configured for MWDMA2
>>> [    4.450267] scsi 1:0:0:0: CD-ROM            QEMU     QEMU CD-ROM      0.8. PQ: 0 ANSI: 5
>>> [    4.464317] ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
>>> [    4.464319] ata2.00: BMDMA stat 0x5
>>> [    4.464339] ata2.00: cmd a0/01:00:00:00:01/00:00:00:00:00/a0 tag 0 dma 16640 in
>>> [    4.464339]          Inquiry 12 01 00 00 ff 00res 48/20:02:00:24:00/00:00:00:00:00/a0 Emask 0x2 (HSM violation)
>>> [    4.464341] ata2.00: status: { DRDY DRQ }
>>> [    4.465864] ata2: soft resetting link
>>> [    4.625971] ata2.00: configured for MWDMA2
>>> [    4.628290] ata2: EH complete
>>> [    4.646670] ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
>>> [    4.646671] ata2.00: BMDMA stat 0x5
>>> [    4.646683] ata2.00: cmd a0/01:00:00:00:01/00:00:00:00:00/a0 tag 0 dma 16640 in
>>> [    4.646683]          Inquiry 12 01 00 00 ff 00res 48/20:02:00:24:00/00:00:00:00:00/a0 Emask 0x2 (HSM violation)
>>> [    4.646685] ata2.00: status: { DRDY DRQ }
>>> [    4.648193] ata2: soft resetting link
>>>
>>> ...
>>>
>>> Fix this by suppressing VPD inquiry for this device.
>>>
>>> Reported-by: Jan Stancek <jstancek@redhat.com>
>>> Tested-by: Jan Stancek <jstancek@redhat.com>
>>> Cc: <stable@vger.kernel.org>
>>> Signed-off-by: Ewan D. Milne <emilne@redhat.com>
>>> ---
>>>  drivers/scsi/scsi_devinfo.c |    1 +
>>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
>>> index bbfbfd9..09bbd3f 100644
>>> --- a/drivers/scsi/scsi_devinfo.c
>>> +++ b/drivers/scsi/scsi_devinfo.c
>>> @@ -228,6 +228,7 @@ static struct {
>>>  	{"PIONEER", "CD-ROM DRM-624X", NULL, BLIST_FORCELUN | BLIST_SINGLELUN},
>>>  	{"Promise", "VTrak E610f", NULL, BLIST_SPARSELUN | BLIST_NO_RSOC},
>>>  	{"Promise", "", NULL, BLIST_SPARSELUN},
>>> +	{"QEMU", "QEMU CD-ROM", NULL, BLIST_SKIP_VPD_PAGES},
>>>  	{"QNAP", "iSCSI Storage", NULL, BLIST_MAX_1024},
>>>  	{"SYNOLOGY", "iSCSI Storage", NULL, BLIST_MAX_1024},
>>>  	{"QUANTUM", "XP34301", "1071", BLIST_NOTQ},
>>>
>> This doesn't apply to all versions of QEMU (upstream qemu works fine),
>> so at the very least it needs to be restricted to a specific version.
> 
> Well, the "0.8." version shown above definitely didn't work.
> 
>>
>> At the same time I'd _rather_ like to figure out why things break in the
>> first place.
>> QEMU CD-ROM claims to support SPC-3, for which VPD pages are mandatory.
>> So why is this error generated?
> 
> Not sure why the error is generated, but if it is, we can't keep sending
> the commands, the guest won't boot.  I guess the real problem is do we
> want to keep finding the problem devices one-by-one, or should we put in
> some logic to e.g. avoid re-reading the VPD pages on rescan if the
> initial scan didn't work.  Seems like a lot of trouble, though, for a
> broken device, and that's what the blacklist is for.
> 
Sure, if the device is misbehaving and we don't have any way of fixing
it, blacklist is the way to go.
But at the same time a recent qemu is proven to work, to blacklisting
everything is too harsh.

So either we dig into what went wrong with qemu 0.8, or we figure out
from which qemu version things start to behave nicely, and blacklist
earlier versions.

>>
>> Either way, this patch is wrong.
> 
> If we can identify which versions work, we can update it.  Otherwise
> I think we have to be conservative.
> 
So far we just had this single report where the upstream kernel didn't
work correctly with a (really old) version of qemu.
Hardly justifying blacklisting qemu CD-ROM in general.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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