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

[Jeff Garzik <jgarzik@pobox.com>]

Brian King wrote:
> James Bottomley wrote:
>> On Fri, 2006-04-28 at 14:03 -0500, Brian King wrote:
>>>> Perhaps you could tell me what the actual failure case is?  
>>> I don't have any data on how ATA/ATAPI devices respond if they receive
>>> too large of a CDB, but my guess is they probably don't react nicely.
>>> Today libata uses the hosts's max_cmd_len for some protection against
>>> this, I was merely trying to continue with a similar level of
>>> protection in my new usage of libata.
>> But how would they receive too large a CDB?  
> 
> I suppose the only real exposure then would be someone doing passthru
> commands in which we could argue that userspace should be smart enough
> not to do things like this.
> 
> Going along with that argument, there's really no good reason for
> libata to be playing games with scsi_host->max_cmd_len based on
> the attached devices.

If both host controller and device support 16-byte CDB, it should not be 
limited to 12 bytes.

libata is not "playing games", just exporting what the hardware supports 
as best the API allows.  It needs to support 16-byte CDBs for the same 
reason any SCSI LLDD supports 16-byte CDBs.

Remember ATAPI<->SCSI bridges exist, thus any SCSI disk can appear 
attached to ATAPI.

	Jeff