linux-kernel - Re: [PATCH] virtio-scsi: Change sense buffer size to 252

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Date:	Thu, 06 Mar 2014 12:55:45 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Hannes Reinecke <hare@...e.de>, Fam Zheng <famz@...hat.com>,
	linux-kernel@...r.kernel.org
CC:	linux-scsi@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] virtio-scsi: Change sense buffer size to 252

Il 06/03/2014 12:22, Hannes Reinecke ha scritto:
> On 03/06/2014 11:09 AM, Paolo Bonzini wrote:
>> Il 06/03/2014 09:47, Fam Zheng ha scritto:
>>> According to SPC-4, section 4.5.2.1, 252 is the limit of sense
>>> data. So
>>> increase the value.
>>>
>>> Signed-off-by: Fam Zheng <famz@...hat.com>
>>> ---
>>>  include/linux/virtio_scsi.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/virtio_scsi.h
>>> b/include/linux/virtio_scsi.h
>>> index 4195b97..a437f7f 100644
>>> --- a/include/linux/virtio_scsi.h
>>> +++ b/include/linux/virtio_scsi.h
>>> @@ -28,7 +28,7 @@
>>>  #define _LINUX_VIRTIO_SCSI_H
>>>
>>>  #define VIRTIO_SCSI_CDB_SIZE   32
>>> -#define VIRTIO_SCSI_SENSE_SIZE 96
>>> +#define VIRTIO_SCSI_SENSE_SIZE 252
>>>
>>>  /* SCSI command request, followed by data-out */
>>>  struct virtio_scsi_cmd_req {
>>>
>>
>> Hi Fam, how did you test this?
>
> Is there a specific reason _not_ to use the linux default?
> The SCSI stack typically limits the sense code to
> SCSI_SENSE_BUFFERSIZE, so using other values have a
> limited sense.
> Literally :-)

Indeed I don't think this patch makes a difference.  Though I asked not 
from the SCSI stack perspective, but because right now both virtio-scsi 
targets (QEMU and vhost-scsi) are also truncating at 96.

Paolo
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