Tejun Heo wrote:
> Douglas Gilbert wrote:
>>> 1) The kernel must prevent 16-byte non-passthru commands from reaching
>>> 12-byte-only ATAPI devices.
>>
>> I would prefer to see the command sent through until
>> it hits a transport that cannot carry a 16 byte cdb.
>> That transport may be in an external enclosure, or
>> the limitation may have been removed.
>
> The host max CDB len has never been a proper protection against illegal
> CDB length. Think about PATA, ata_piix SLAVE_POSS or PMP cases sharing
> the host w/ ATA devices. Max CDB len is always 16 in such cases whether
> an ATAPI device supports 12 or 16 byte CDB. Also, max CDB len doesn't
> protect against smaller CDB (12 bytes) when the device supports 16 byte
> CDBs.
>
> So, for some cases, we had protection and in many others we didn't.
> We've always depended on applications sending correctly sized CDBs and
> ATAPI devices aborting wrong sized CDBs.
>
> I'm not sure whether the protection is necessary, but if it is, we can
> do the protection *properly* by moving cdb restriction to lower level
> such that it's applied per-device not per-host. This also solves the
> 16byte passthrough problem.
>
> IMHO, this issues is separate from SAT passthrough and needs
> improvements regardless.
>
>>> 2) Existing in-the-field solutions that issue commands such as BLANK or
>>> a vendor-reserved 0x85 opcode must continue working, without recompile.
>>
>> Opcodes 0x85 and 0xa1 are not vendor reserved. They have
>> been reserved for t10.org use since SCSI-2. Other SCSI
>> opcode ranges are set aside for vendor use.
>> The BLANK problems remains.
>
> Ah.. I haven't thought about opcode clash. I'm all ears on this. Just
> tell me what to do, I'll go and implement it.
Tejun,
To summarize:
- there should never be vendor specific commands at
SCSI opcodes 0x85 and 0xa1
- referring the Annex D.3.2 in spc4r07a.pdf (www.t10.org)
opcode 0x85 (APT (16)) does not clash with anything.
Opcode 0xa1 (APT (12)) clashes with the BLANK command
defined for MMC devices
The BLANK command (mmc5r03c.pdf section 6.2) seems to be
mandatory for drives that support writing to CD-RW and DVD-RW
media. That implies opcode 0xa1 should go through the SATL
to an ATAPI CD/DVD drive. Should it go through to an ATAPI
tape drive?
Given the APT (12) will not be available for ATAPI CD/DVD
drives, it is important that APT (16) (i.e. opcode 0x85)
works properly (i.e. implements the SAT ATA PASS THROUGH
logic).
Doug Gilbert
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