Re: [PATCH 1/2] scsi: Add scsi_device max_cmd_len

[Brian King <brking@us.ibm.com>]

Jeff Garzik wrote:
> Brian King wrote:
>> Jeff Garzik wrote:
>>> James Bottomley wrote:
>>>> This really doesn't look correct.  What you want is a sata transport
>>>> class with a max command length in the host device.
>>> Christoph Hellwig wrote:
>>>> this sounds wrong to me.  cdb length is a limitation of the host (driver).
>>>> A target will reject unknown commands, no matter what length they have.
>>> In practice, CDB length may be limited by both the host and the device. 
>>>   This applies to ATAPI, and some USB storage too IIRC.  For ATAPI, you 
>>> read the CDB length from the device's IDENTIFY PACKET DEVICE info page.
>> So the question remains, do we need to police the CDB length on a per device
>> basis, or is a per host basis ok? Will we have ATAPI devices falling on the
>> floor if they get sent too large of a cdb?
> 
> It _must_ be limited by both device and host.  If you have a device that 
> supports 16-byte CDBs and a host controller which only supports 12-byte 
> CDBs, clearly the limit is 12, due to host.  However, a reversed 
> situation (limited by device) is equally plausible/possible.

Ok. That is what I was assuming, which was the reason I submitted this
patch in the first place.

James, given this information, are you ok with the patch, or do you
still have an objection?

Thanks,

Brian

-- 
Brian King
eServer Storage I/O
IBM Linux Technology Center