Re: [PATCH] libata: add support for ATA_16 commands to ATAPI devices

[Jeff Garzik <jeff@garzik.org>]

Alan wrote:
>> I do not wish to completely eliminate the current behavior, which passes 
>> through all opcodes to the ATAPI device.  You cannot guarantee that 
>> ATA_16 is never used for a vendor-reserved opcode, for example.
> 
> For 16 byte commands via SG_IO you know the command is 16 bytes long as
> the command length is passed in hdr->cmd_len which becomes rq->cmd_len.
> Is that not sufficient to avoid this ATA_16 test if you pass it on to the
> required functions ?

Well, its a question of whether you are executing the supplied cdb as an 
ATA command or a SCSI command.  If executing as an ATA command, libata 
needs to intercept it (as Mark's patch does), because few if any ATAPI 
devices support the ATA_16 command in the firmware.

The current behavior treats everything as SCSI commands, passed to the 
firmware (if a bit massaged, a la INQUIRY), which means there is no way 
for userspace to directly address the underlying ATA bus outside of 
libata-scsi.

Or am I misunderstanding things completely?  :)

	Jeff