Re: [PATCH] remove ide-scsi

Sergei Shtylyov
2008-12-07T15:21:19Z

Hello.

James Bottomley wrote:

>>>> Oh, yes. SCSI emulation is just what Linux embedded world is asking
>>>> for...
>>>>
>>>>
>>> Well ATAPI is SCSI emulation (its a sort of pidgin SCSI admittedly).
>>>
>>>
>> ATAPI is SCSI transport (with maybe some quirks at SCSI command level
>> tho, IIRC). ATA is neither thansport nor does it map to SCSI 1:1.
>>
>
>
> Well, to be wholly accurate, since SCSI-3, SCSI has been separated into
> an architecture, primary command, device specific command and transport
> model (called the SCSI architecture model).

Thanks, I'm well aware of all this. :-)
My first encounter with SCSI dates back to 1993-94 -- it's a pity
that I had to abandon this area (switching to that puny IDE ;-)...

> Starting with ATA-8, ATA
> will go this way again.

It's gone that way in ATA/PI-7 actually, being broken into 3 separate
documents then, one spoecifying the command set and 2 others PATA and
SATA tranports.

> What ATAPI actually is is a SCSI (really MMC
> for CD and SSC for tape)

Unfortunately, the initial SFF documents specified both the transport
protocol and the command sets (which somewhat diverged form what SCSI-2
had, IIRC).
Fortunately, once ANSI finally taken over ATAPI work, they dropped
that stupid practice and started referring to MMC and SSC.

> command transported over ATA using the ATA
> PACKET command. With ATA-8 it will be much more analogous to SCSI
> command over ATA transport.
>

I don't think "analogous" means that it will be sending SCSI CDBs
over PATA/SATA is of native commands and turn ATA into ATAPI. So all
this is fine but changes nothing about the SCSI emulation thing.

>> The code for emulating SCSI on ATA only burdens the kernel (and causes user
>> complaints about changing disk names from /dev/hdx to /dev/sda :-).
>>
>
> The code for sorting this out is already upstream in the block tree for
> 2.6.29.
>

Sorting out what, emulation?

I have to cut my response short that that point. I must be totally
crazy to allow myself to be dragged into this discussion having so much
work to do... :-/

MBR, Sergei