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

[Jeff Garzik <jgarzik@pobox.com>]

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.

	Jeff