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Date:      Wed, 27 Jun 2012 18:33:45 +0300
From:      Alexander Motin <mav@FreeBSD.org>
To:        Hans Petter Selasky <hselasky@c2i.net>
Cc:        freebsd-usb@freebsd.org
Subject:   Re: [usb] Kingston 8Gb is not usable
Message-ID:  <4FEB27D9.9030408@FreeBSD.org>
In-Reply-To: <201206271731.08298.hselasky@c2i.net>
References:  <4FE9AB28.3070704@passap.ru> <201206271717.02962.hselasky@c2i.net> <4FEB269E.6000508@FreeBSD.org> <201206271731.08298.hselasky@c2i.net>

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On 06/27/12 18:31, Hans Petter Selasky wrote:
> On Wednesday 27 June 2012 17:28:30 Alexander Motin wrote:
>> On 06/27/12 18:17, Hans Petter Selasky wrote:
>>> On Wednesday 27 June 2012 17:08:29 Alexander Motin wrote:
>>>> umass problem
>>>
>>> Hi,
>>>
>>> Are you verifying the received data length for the SCSI commands reading
>>> out various data?
>>
>> Mentioned revision beyond others adds check for the sense data length in
>> case of error. It won't even look into the sense data if reported amount
>> (sense_len - sense_resid) is zero or less then needed. I have no idea
>> how USB calculates resid, but it may be a problem in this case. I think
>> it could be useful to get USB packets trace to see whether it is device
>> doesn't return any sense data, or umass improperly interprets them in
>> this case for some reason.
>
> Hi,
>
> The residue is part of the 13 status bytes in the SCSI BOT protocol. If this
> field is zero, the umass driver will compute the residue from the actual data
> transferred as a workaround.

Can't there be an opposite bug -- residue field is equal to the transfer 
size in which case CAM will think there is no sense data?

-- 
Alexander Motin



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